Characteristics of flow field near sea bottom in a combined wave and current motion

Abstract

A reasonable time‐invariant eddy viscosity model is proposed to describe turbulent flow over a rough sea bottom in a combined wave‐current system. The linearized governing equations are solved for the wave and current kinematics both inside and outside the wave boundary layer. The results of velocity profile, friction factor and apparent roughness in a wave‐current motion are presented. The friction factors are shown to be consistent with previous theoretical results for the limiting cases of pure wave and pure current motions. Present results are compared favorably with the available data.     

Determination of deuterium site occupancy in ZrCoD3 and its role in improved durability of Zr–Co–Ni deuterides against disproportionation

In the present study, we have for the first time reported the occupancy of deuterium in a new interstitial site of ZrCoD₃ which explain the hydrogen induced disproportionation behavior of ZrCo alloy. We have also reported the effect of Ni substitution on interstitial site occupancy of deuterium in ZrCo_1−xNi_xD₃, which in turn explains the improved durability of these Ni substituted deuterides against disproportionation. The crystal structure of the ZrCo_1−xNi_x (x = 0.0, 0.1, 0.2, 0.3) deuterides was investigated by X-ray powder diffraction and neutron diffraction methods. The XRD data reveals a single phase formation for all deuterides with varying Ni content (x). The neutron diffraction study shows that deuterium occupies a new site 8e in addition to 4c₂ and 8f₁. Additionally, the Zr–D distance in 8e site is shorter than that in ZrD₂. Therefore, increase in 8e site occupancy will in turn decreases the durability against disproportionation and vice-versa. Furthermore, the neutron diffraction reveals that occupancy of new 8e site decreases and its Zr–D distance increases with increase in Ni content, which explicate the higher durability against disproportionation for Ni rich compound.     

Sub-microsecond X-ray crystallography: techniques,challenges, and applications for materials science

Dynamics of crystals is a subject of recent interest in solid-state physics and a challenge for modern X-ray crystallography. Time-dependent response of solids to an external perturbation on atomic and microstructural length scales is the key to understanding many physical properties. This paper reviews the challenges and opportunities for probing of sub-micro-, micro-, and millisecond dynamics of solids using the methods of X-ray crystallography. It starts with an overview of recent time-resolved X-ray diffraction techniques. It then focuses on the processes that are important for understanding functional materials: dynamics of ferroelectric and ferroelastic domain patterns, texture in piezoelectric ceramics, mechanical resonances in solids, and dynamics of structural disorder. Knowledge available from macroscopic experiments is summarized, and opportunities for X-ray crystallography to resolve existing controversies are presented. This paper suggests the possible synergy of macroscopic and X-ray crystallographic experimental techniques.     

Monitoring of CO2 geological storage based on the passive surface waves

Carbon dioxide (CO₂) capture and geological storage (CCS) is one of promising technologies for greenhouse gas effect mitigation. Many geotechnical challenges remain during carbon dioxide storage field practices, among which effectively detecting CO₂ from deep underground is one of engineering problems. This paper reviews monitoring techniques currently used during CO₂ injection and storage. A method developed based on measuring seismic microtremors is of main interest. This method was first successfully used to characterize a site in this paper. To explore its feasibility in CO₂ storage monitoring, numerical simulations were conducted to investigate detectable changes in elastic wave signatures due to injection and geological storage of CO₂. It is found that, although it is effective for shallow earth profile estimation, the surface wave velocity is not sensitive to the CO₂ layer physical parameter variations, especially for a thin CO₂ geological storage layer in a deep underground reservoir.     

Oxidation of potential SOFC interconnect materials,Crofer 22 APU and Avesta 353 MA,in dry and humid air studied in situ by X-ray diffraction

Abstract

Several stainless steels have been developed for the use as interconnect materials in solid oxide fuel cells in order to reduce costs, while maintaining the required performance. The materials however, are subjected to humid air, at high temperatures up to 800°C leading to enhanced oxidation. High temperature X-ray diffraction, combined with field emission – scanning electron microscopy, has been applied to study in situ the influence of water vapour on the chromia scale formation on the ferritic Crofer 22 APU and the austenitic Avesta 353 MA alloys in comparison to their dry air oxidation behaviour. Both materials form at 800°C, during the first 100h exposure, Cr₂O₃ and MnCr₂O₄, the latter mostly in the surface region of the oxide scale. Additionally, Crofer 22 APU forms internal Al₂O₃ precipitates, while on Avesta 353 MA a SiO₂ layer is found beneath the outer oxide scale. High temperature XRD indicates stress formation and relaxation in the Cr₂O₃ scale formed in humid air, especially for Crofer 22 APU.     

Polyaniline sensitized Pt@TiO2 for visible-light-driven H2 generation

Polyaniline is a typical conducting polymer with high migration electron rate, good stability, eco-friendly properties, and high absorption coefficients for visible light. In the present study, polyaniline decorated Pt@TiO₂ for visible light-driven H₂ generation is reported for the first time. The above-mentioned nanocomposite is prepared through a simple oxidative-polymerization and characterized by infrared spectroscopy, transmission electron microscopy, X–ray diffraction, thermogravimetric analysis, and ultraviolet–visible diffuse reflectance spectra. Polyaniline modification improves the absorption of the nanocomposite in visible light region via a photosensitization effect similar to dye–sensitization but does not influence the crystal structure and size of Pt@TiO₂. The polyaniline modified Pt@TiO₂ exhibits a remarkable visible light activity (61.8 μmol h⁻¹ g⁻¹) and good stability for H₂ generation (with an average apparent quantum yield of 10.1%) with thioglycolic acid as an electron donor. This work provides new insights into using conducting polymers, including polyaniline, as a sensitizer to modify Pt@TiO₂ for visible-light hydrogen generation.     

Full-scale experimental investigation on the shock-wave characteristics of high-pressure natural gas pipeline physical explosions

In this study, a series of full-scale high-pressure natural gas pipeline physical explosion experiments were performed, in which the overpressure of the shock waves was measured and analyzed. The concept of “physical explosion linear energy (PEXLE)” was proposed and a “PEXLE model” was established to evaluate shock waves in a cylindrical pipeline with high length–diameter ratio. Equations were fitted to describe the characteristics of peak overpressure, positive pressure duration and specific impulse. Results showed that peak overpressure of shock waves is not influenced by the length of pipeline. With the increase of the propagation distance, specific impulse first increases and then decreases. This indicates that the position of the maximum value of overpressure does not correspond with that of the specific impulse.     

Fabrication and electromagnetic wave absorption property of quartz ceramics with a gradient distribution of BaTiO3

Quartz ceramics with a uniform/gradient distribution of BaTiO₃ (U/G–SO–BTO) are fabricated by cold pressing a powder blend with BTO followed by sintering and using a combined technique of spreading the powder blends with gradually increased BTO layer–by–layer and sintering. The electromagnetic wave absorption properties of these two ceramics are studied in detail. For U–SO–BTO samples, the primary electromagnetic reflection is strong due to the aggravated impedance mismatch at their surfaces. The electromagnetic wave reflectivity of U–SO–BTO could only reach ?7.0?dB when the sample thickness is 6?mm and the BTO content is 8.0?wt%, and it decreases slightly to ?8.1?dB when the sample thickness is increased to 10.0?mm and the BTO content is decreased to 5.0?wt% simultaneously. For G–SO–BTO samples, electromagnetic waves could enter with little reflection due to the weak surface impedance mismatch, and the electromagnetic waves entering these samples could propagate forward while being absorbed gradually with little reflection because of the weak impedance mismatch at the interfaces. The G–SO–BTO samples are promising excellent electromagnetic absorbing materials because their electromagnetic wave reflectivity could reach a level lower than ?12.0?dB and could decrease further from –12.2 to ?13.1?dB as the layer thickness increases from 1.0 to 2.0?mm.     

An experimental study on the oscillation of the propagating syngas-air flame in a duct

In this paper, premixed syngas-air flame propagating from the open end to the closed end were experimentally investigated. The effects of equivalence ratios, 0.8 ≤ Ф ≤ 1.2, and hydrogen volume fractions, 10% ≤ α(H₂) ≤ 90%, on flame deformation and oscillation had been discussed in detail. The tulip-like flame was observed because of the large pressure gradient. Results indicate that the pressure wave plays an important role in the flame deformation and oscillation. The flame oscillates as hydrogen volume fraction varies. There are two oscillation modes. When the flame oscillates as mode Ⅰ, the flame first oscillates smoothly, then the oscillation is gradually enhanced, and finally the oscillation decays. The interaction of flame and pressure waves continuously stimulates the flame deformation and oscillation, finally the violent flame folding emerges in the later stage. When the flame oscillates as mode Ⅱ, the flame just oscillates violently in the early stage.     

水热法主要提取因素对光皮木瓜多糖结构的影响

目的 优化水热法提取光皮木瓜（Chaenomeles sinensis）多糖的提取工艺条件，对光皮木瓜不溶性多糖的组成和结构进行分析。方法 预处理后的光皮木瓜样品经水热法提取、抽滤、冲洗，浓缩等操作，分别得到不溶性多糖、醇沉多糖和醇溶多糖，通过傅里叶变换红外光谱、扫描电子显微镜及X射线衍射分析不溶性多糖的组成和结构。 结果 多糖提取的较优条件为150 ℃/45 min，料液比1∶10 (W/V)；温度对水热法提取效果影响显著，适当升高温度、延长提取时间和减少料液比有利于多糖提取；高温虽能促进半纤维素溶解，但无法使木质素和木聚糖降解；即使提取温度不同，光皮木不溶性多糖的结构差异也极小；水热法提取光皮木瓜多糖不会导致多糖的功能性基团变化，只改变多糖的化学组成。结论 该研究可为光皮木瓜多糖的结构与功能研究提供实验依据，也为陕西白河光皮木瓜资源的综合利用提供研究参考。