5,004 research outputs found

    High Performance Electrocatalysts Based on Pt Nanoarchitecture for Fuel Cell Applications

    Get PDF
    Fuel cells, converting chemical energy from fuels into electricity directly without the need for combustion, are promising energy conversion devices for their potential applications as environmentally friendly, energy efficient power sources. However, to take fuel cell technology forward towards commercialization, we need to achieve further improvements in electrocatalyst technology, which can play an extremely important role in essentially determining cost-effectiveness, performance, and durability. In particular, platinum- (Pt-) based electrocatalyst approaches have been extensively investigated and actively pursued to meet those demands as an ideal fuel cell catalyst due to their most outstanding activity for both cathode oxygen reduction reactions and anode fuel oxidation reactions. In this review, we will address important issues and recent progress in the development of Pt-based catalysts, their synthesis, and characterization. We will also review snapshots of research that are focused on essential dynamics aspects of electrocatalytic reactions, such as the shape effects on the catalytic activity of Pt-based nanostructures, the relationships between structural morphology of Pt-based nanostructures and electrochemical reactions on both cathode and anode electrodes, and the effects of composition and electronic structure of Pt-based catalysts on electrochemical reaction properties of fuel cells.</jats:p

    Branes in the plane wave background with gauge field condensates

    Full text link
    Supersymmetric branes in the plane wave background with additional constant magnetic fields are studied from the world-sheet point of view. It is found that in contradistinction to flat space, boundary condensates on some maximally supersymmetric branes necessarily break at least some supersymmetries. The maximally supersymmetric cases with condensates are shown to be in one to one correspondence with the previously classified class II branes.Comment: LaTeX, 31 pages, no figures; v2: references added, some typos correcte

    Phase Transitions in the Two-Dimensional XY Model with Random Phases: a Monte Carlo Study

    Full text link
    We study the two-dimensional XY model with quenched random phases by Monte Carlo simulation and finite-size scaling analysis. We determine the phase diagram of the model and study its critical behavior as a function of disorder and temperature. If the strength of the randomness is less than a critical value, σc\sigma_{c}, the system has a Kosterlitz-Thouless (KT) phase transition from the paramagnetic phase to a state with quasi-long-range order. Our data suggest that the latter exists down to T=0 in contradiction with theories that predict the appearance of a low-temperature reentrant phase. At the critical disorder TKT→0T_{KT}\rightarrow 0 and for σ>σc\sigma > \sigma_{c} there is no quasi-ordered phase. At zero temperature there is a phase transition between two different glassy states at σc\sigma_{c}. The functional dependence of the correlation length on σ\sigma suggests that this transition corresponds to the disorder-driven unbinding of vortex pairs.Comment: LaTex file and 18 figure

    OGLE-2017-BLG-1522: A giant planet around a brown dwarf located in the Galactic bulge

    Full text link
    We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of tE∼7.5t_{\rm E} \sim 7.5 days. The Einstein radius is unusually small, θE=0.065 \theta_{\rm E} = 0.065\,mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses (Mhost,Mplanet)=(46−25+79,0.75−0.40+1.26) MJ(M_{\rm host}, M_{\rm planet})=(46_{-25}^{+79}, 0.75_{-0.40}^{+1.26})~M_{\rm J} and source-lens distance DLS=0.99−0.54+0.91 kpcD_{\rm LS} = 0.99_{-0.54}^{+0.91}~{\rm kpc}, implying that this is a brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location that is also consistent with the relatively low lens-source relative proper motion μ=3.2±0.5 mas yr−1\mu = 3.2 \pm 0.5~{\rm mas}~{\rm yr^{-1}}. The projected companion-host separation is 0.59−0.11+0.12 AU0.59_{-0.11}^{+0.12}~{\rm AU}, indicating that the planet is placed beyond the snow line of the host, i.e., asl∼0.12 AUa_{sl} \sim 0.12~{\rm AU}. Planet formation scenarios combined with the small companion-host mass ratio q∼0.016q \sim 0.016 and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown dwarf host.Comment: 20 pages, 6 figure
    • …
    corecore