Heat Transfer Characteristics of an Innovative Thermal Protection System Based on Photonic Crystals

In order to protect the internal components of an aircraft from the damage caused by high temperature and heat flux, an effective thermal protection structure must be designed and developed. In this paper, heat transfer characteristics for an innovative thermal protection coating structure are investigated, based on three-dimensional photonic crystals (SiC-3D PCs). The actual system with coating material, containing photonic crystals, is simplified as a macroscopic model of one-dimensional coupled conduction–radiation heat transfer among three layers composed of semitransparent media. Moreover, according to preliminary physical parameters, heat transfer profiles and thermal protection efficiency for the whole system are estimated. In addition, the effect of the photonic crystals part is analyzed.     

Ionomer content effects on the electrocatalyst layer with in-situ grown Pt nanowires in PEMFCs

The effects of ionomer contents were investigated in composite electrodes with in-situ grown single crystal Pt nanowires (Pt-NWs) for PEMFCs, including the amount in the carbon matrix and impregnated on the surface of the electrocatalyst layer. The electrocatalyst layer was prepared by growing Pt-NWs directly on the carbon matrix with a simple one-step wet chemical approach at room temperature. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), polarization curve tests, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were employed to evaluate the ionomer effects. The experimental results showed that the ionomer in the carbon matrix had an influence on the ionic conductivity and aggregation and distribution of the Pt-NWs, and the ionomer impregnated on the surface of the electrocatalyst layer affected the mass transport and ionic conductivity. The performance of the MEA was improved by optimizing the ionomer contents.     

Solid state reaction synthesis and photoluminescence properties of Dy3+ doped NaGd(MoO4)2 phosphor

Dy³⁺ doped NaGd(MoO₄)₂ phosphors were synthesized by a traditional solid-state reaction route using NH₄HF₂ as a flux. The influence of calcination temperature on the crystal structure and spectral properties was studied, and the optimum calcination temperature for producing Dy³⁺ doped NaGd(MoO₄)₂ phosphor was experimentally confirmed. The concentration quenching of Dy³⁺ fluorescence and excitation-wavelength dependent spectroscopic properties were studied. On the base of both the Van Uitert's and I-H models, the electric dipole–dipole (D–D) interaction was ascribed to be the main physical mechanism responsible for energy transfer between Dy³⁺ ions. It was also discovered that the color coordinates of the Dy³⁺ doped NaGd(MoO₄)₂ phosphor depends on the Dy³⁺ doping concentration and the excitation wavelength.     

Effects of coherency stress and vacancy sources/sinks on interdiffusion across coherent multilayer interfaces – Part II: Interface sharpening and intermixing rate

Vacancy-mediated interdiffusion in coherent Mo/V and Cu/Ni multilayers is simulated to evaluate the effects of coherency stress and vacancy sources/sinks on interface sharpening and the intermixing rate, using the phase field model developed in a previous paper for two limiting cases: ideal vacancy sources/sinks densely distributed or not present at all. Interface sharpening stems from a large diffusion coefficient asymmetry across the interface, which in turn originates from the large difference in vacancy formation and migration energies between the two constituent layers. Remarkable sharpening is found in Mo/V multilayers either with dense or without vacancy sources/sinks, but only in Cu/Ni with a high density of sources/sinks. Sharpening is suppressed by coherency stress in Cu/Ni regardless of the existence of vacancy sources/sinks, but only promoted in Mo/V with a high density of sources/sinks. The intermixing rate is suppressed in Mo/V by the introduction of a high density of vacancy sources/sinks that are parallel or perpendicular to the interfaces, or uniformly distributed in all orientations, but only promoted in Cu/Ni by the introduction of vacancy sources/sinks that are parallel to the interfaces. The intermixing rate is promoted in Mo/V by coherency stress regardless of the existence of vacancy sources/sinks, but promoted in Cu/Ni by coherency stress only when the vacancy sources/sinks are parallel to the interface or not present at all. The effects of that part of coherency stress induced by the mismatch in atomic volumes on interface sharpening and the intermixing rate are opposite to, but dominant over, those of the stress induced by lattice creation/annihilation in vacancy sources/sinks.     

Design of the HL-2M power supply control system

The power supply control system is one of the most important local control systems of HL-2M tokamak. The power supply system of HL-2M is composed of four flywheel generator sets with total capacity of 600 MVA, all the magnetic field coil power supplies and high voltage power supplies of auxiliary heating system. The control system of power supply should make sure the large amount of on-site equipment and facilities to operate steadily and reliably.This paper presents the architecture of HL-2M control system and four kinds of established control networks. It describes how the power supply control system is built by using the established hardware structures and software agreements. Specially, it is focused on introducing an application of real-time technology based on the reflective shared memory and the fully digital compact solution for controlling the high power converters. Otherwise, a scheme which adopts PROFINET and Sequence of Events technology to carry out the intellect interlock control system is given.     

Fractal characterization of ceramic crack patterns after thermal shocks

This work utilized a combination of experimental evidence and fractal geometric method to assess the effect of crack extension concerning the thermal shock on residual strength of ceramics. Sintered alumina (Al₂O₃) ceramic slabs were bundled and quenched in water under different thermal shock temperatures. The fractal dimension of thermal shock crack patterns on the interior surface and the cooled surface was calculated by the Box-counting method. Fracture energy of a fractal pattern of microcracks in quasi-brittle solids was employed to explain the relationship between crack length and fractal dimensions. The results show that if the crack propagation has the same crack length but a larger fractal dimension, it will absorb more fracture energy. The thermal shock crack patterns of Al₂O₃ ceramics with different grain sizes were analyzed, and the smaller grain size ceramic had a higher fractal dimension of crack patterns than the larger one.     

A theoretical study of the ability of 2D monolayer Au (111) to activate gas molecules

The adsorption and activation of gas molecules are investigated substantially in solid-gas heterogeneous catalysis. Here we investigated the interaction between gas molecules and unique two-dimensional monolayer Au (111) structure using density functional theory. It is found that CO₂, H₂O, N₂ and CH₄ molecules are weakly adsorbed on the surface with the adsorption energies between ?0.150 and ?0.250 eV due to van der Waals interaction. While CO, NO, NO₂, and NH₃ molecules are adsorbed more stably with the adsorption energies between ?0.300 and ?0.470 eV. Especially, the bond length of CO is stretched by 0.038 Å and the bond angle of NO₂ is obviously enlarged by 10.460°. The activation originates from the rearrangement of molecule orbitals and the orbitals hybridization between the partial orbitals of gas molecules and Au-5d orbitals. The fundamental analyses of adsorption mechanism and electronic properties may provide guidance for the applications of two-dimensional monolayer metal catalysis.PACSnumbers 73.22.-f, 73.61.-r     

Effect of [6,6]‐phenyl‐C61‐butyric acid methyl ester on the morphology of poly(3‐hexylthiophene) film

The change of morphology of poly(3‐hexylthiophene) (P3HT) film as a result of blending with [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) was studied using a freeze‐dry method. A porous structure was observed as the P3HT/PCBM solution was freeze‐dried. The pore size decreased as the proportion of PCBM increased in the P3HT/PCBM blended film. Additionally, the freeze‐dried P3HT/PCBM film was more resistant to the formation of PCBM crystals than that prepared by a spin‐coating method during the thermal annealing process. Homogeneous distribution of PCBM in the freeze‐dried P3HT/PCBM film was the main reason for the reduction of large PCBM crystal formation. Copyright © 2011 Society of Chemical Industry     

Hydrogen adsorption on and diffusion through MoS2 monolayer: First-principles study

We investigate the hydrogen adsorption on and diffusion through the MoS₂ monolayer based on density-functional theory. We show that the hydrogen atom prefers to bond to the S atom at the monolayer, leading to enhanced conductivity. The hydrogen atom can also adsorb at the middle of the hexagon ring by overcoming an energy barrier of 0.57 eV at a strain of 8%. Also, we show that the MoS₂ monolayer is flexible and any mechanical deformation of the monolayer is reversible because the extension of the Mo–S bond is much smaller than the applied strain. The monolayer can block the diffusion of hydrogen molecule from one side to the other due to a high energy barrier (6.56 eV). However, the barrier can be reduced to 1.38 eV at a strain of 30% and even totally removed by creating S vacancies and applying a strain of 15%. The MoS₂ monolayer may find applications in sensors to detect hydrogen, and as mechanical valve to control the concentration of hydrogen gas.