Due to their environmental sustainability and high efficiency, proton-exchange-membrane fuel cells (PEMFCs) are expected to be an essential type of energy source for electric vehicles, energy generation, and the space industry in the coming decades. Here, the recent developments regarding shape-controlled nanostructure catalysts are reviewed, with a focus on the stability of high-performance Pt-based catalysts and related mechanisms. The catalysts, which possess great activity, are still far from meeting the requirements of their applications, due to stability issues, especially in membrane electrode assemblies (MEAs). Thus, solutions toward the comprehensive performance of Pt-based catalysts are discussed here. The research trends and related theories that can promote the application of Pt-based catalysts are also provided.
Abstract-A polarimetric scattering from two-dimensional (2-D) rough surface is presented by the finite-difference time-domain (FDTD) algorithm.The FDTD calculations with sinusoidal and pulsed plane wave excitations are performed. As the sinusoidal FDTD is concerned, it is convenient to obtain the scattered angular distribution of normalized radar cross section (NRCS) from rough surface for a single frequency. And the advantage of pulsed FDTD is to calculate the frequency distribution of NRCS from rough surface in a scattered direction of interest. A single frequency scattering from rough surface by sinusoidal FDTD is validated by the result of Kirchhoff Approximation (KA). And the frequency response of rough surface by pulsed FDTD is verified by that of sinusoidal FDTD, which requires an individual FDTD run for every frequency. To save computation time, the MPI-based parallel FDTD method is adopted. And the computation time of parallel FDTD algorithm is dramatically reduced compared to a single-process implementation. Finally, the polarimetric scattering of rough surface with the sinusoidal and pulsed FDTD illumination are presented and analyzed for different polarizations.
A dual-linearly-polarized, electrically small, low-profile, broadside radiating Huygens dipole antenna is presented that is an advanced combination of electric and magnetic near-field resonant parasitic (NFRP) elements. Its prototype was fabricated and tested. The measured results are in good agreement with their simulated values. At 1.515 GHz the prototype is electrically small (ka = 0.904) and low profile (0.0483λ 0). It exhibits high port isolation and a large front-to-back ratio (FTBR). The isolation between its two ports is demonstrated to be over 25.8 dB within its-10-dB fractional impedance bandwidth (FBW), 0.46%. When port 1 (port 2) is excited, the peak realized gain is 2.03 dBi (2.15 dBi) strictly along the broadside direction with a 12.4 dB (12.1 dB) FTBR.
Abstract-This paper presents an investigation for the electromagnetic scattering characteristic of the 2-D infinitely long target located above two-layered 1-D rough surfaces. A finite-difference time-domain (FDTD) approach is used in this study, and the uniaxial perfectly matched layer (UPML) medium is adopted for truncation of FDTD lattices, in which the finite-difference equations can be used for the total computation domain by properly choosing the uniaxial parameters. The upper and lower interfaces are characterized with Gaussian statistics for the height and the autocorrelation function. For the composite scattering of infinitely long cylinder and underlying single-layered rough surfaces as an example, the angular distribution of scattering coefficient with different incident angles is calculated and it shows good agreement with the numerical result by the conventional method of moments. And the influence of some parameters related to the twolayered rough surfaces and target on composite scattering coefficient is investigated and discussed in detail.
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