船舶水润滑尾轴承结构设计研究进展

水润滑轴承的结构优化可以有效提高轴承的承载能力、冷却散热、减振降噪和摩擦学性能。在概述船舶水润滑尾轴承的优势和存在问题的基础上,分析归纳水润滑尾轴承内衬结构、内衬的厚度和硬度、轴承间隙、长径比、内衬表面粗糙度等结构设计参数的研究进展;以轴位水润滑尾轴承、内衬多层复合水润滑尾轴承和闭式水润滑尾轴承为例,介绍近年来几种新型水润滑尾轴承的结构设计,指出闭式水润滑尾轴承在内河及沿海船舶上具有广阔的应用前景,是未来的研究重点和发展趋势;建议水润滑尾轴承的研究应从以下方面着手,一是从微纳米尺度研究轴承微观界面润滑机制,二是在考虑轴承参数间耦合作用的基础上对轴承进行多目标优化,三是进一步研究闭式水润滑尾轴承及密封装置材料、结构和辅助装置以及水润滑添加剂,四是研究船舶水润滑尾轴承的设计规范,建立一定范围内精度满足工程需要的轴承设计计算经验公式,以简化轴承设计程序。     

Low temperature heat capacity measurements of β-Si3N4 and γ-Si3N4: Determination of the equilibrium phase boundary between β-Si3N4 and γ-Si3N4

Isobaric heat capacities of β-Si₃N₄ and γ-Si₃N₄ were measured at temperatures between 1.8 and 309.9 K with a thermal relaxation method. The measured heat capacities of γ-Si₃N₄ are smaller than those of β-Si₃N₄ in this temperature range. Using these data, we determined the standard entropies of β-Si₃N₄ and γ-Si₃N₄ to be 62.30 J·mol⁻¹ K⁻¹ and 51.79 J·mol⁻¹ K⁻¹, respectively. The equilibrium phase boundary between β-Si₃N₄ and γ-Si₃N₄ was calculated using these values and thermodynamic parameters reported in previous studies. The obtained equilibrium phase transition pressure at 2000 K is 11.4 GPa. It is lower than the experimental pressures at which γ-Si₃N₄ was synthesized in previous studies. The calculated Clapeyron slope at this temperature is 0.6 MPa K⁻¹, which is consistent with those of theoretical studies.     

Potential application of metal-organic frameworks (MOFs) for hydrogen storage: Simulation by artificial intelligent techniques

Metal-organic frameworks are a new class of materials for hydrogen adsorption/storage applications. The hydrogen storage capacity of this structure is typically related to pressure, temperature, surface area, and adsorption enthalpy. Literature provides no reliable correlation for estimating the hydrogen uptake capacity of MOFs from these easy-measured variables. Therefore, this study introduces several straightforward and accurate artificial intelligence (AI) techniques to fill this gap, initially determining the appropriate topology of AI-based methods, then comparing their performances by statistical criteria, and introducing the most accurate. This study used artificial neural networks, hybrid neuro-fuzzy systems, and support vector machines as estimators. The general regression neural networks (GRNN) with a spread of 7.92 × 10⁻⁴ shows the highest correlation with the literature data and provides a relative absolute deviation of 5.34%, mean squared error of 0.059, and coefficient of determination of 0.9946.     

压缩合成食品对人体运动能力的影响

研究选取12名生理指标相对类似的试验对象,通过采用自身对照和交叉平衡的试验设计方法,针对普通膳食和以90军用干粮为例的压缩合成食品对人体运动能力的影响进行了分析,通过测定试验对象进食2组不同营养组成的食品进行运动或训练后、恢复体内的血糖浓度水平、血乳酸浓度、血乳酸清除率、心率变化、相关激素水平变化以及不同氧化变化情况评价普通膳食和压缩合成食品对人体运动能力的影响。试验结果显示,相比于普通膳食,压缩合成食品在高强度运动以及力竭运动后维持人体运动能力方面以及体能恢复方面具有明显优越性。     

Construction of CO3O4 derived ZIF/GO electrode for outstanding stability in supercapacitors devices

The growing global demand for energy supply and environmental protection has led to the use of high-efficiency energy storage devices, which supercapacitors are used as one of these devices with high storage capacity and exceptional stability. To be used for this purpose, an easy and rapid synthetically method was used to produce the CO₃O₄/GO nanocomposite, and its electrochemical performance as the electrode material in hybrid-supercapacitors was further investigated. In this nanocomposite, the CO₃O₄ crystals with less than 500 nm particle size are uniformly in contact with the wrinkled GO sheets, that their structure and morphology were investigated by surface analyzes. In addition, the functional groups, crystallographic properties, and elemental composition were investigated using the FTIR, XRD, and EDX analyzes. To confirm the supercapacitive effectiveness of the prepared samples, the electrochemical measurements (EIS, CV, and GCD) were done. The results have shown that the values of specific capacity, energy and power densities of Co₃O₄/GO hybrid nanocomposite are 234 mAh g^?1, 16.075 W h kg^?1 and 251 W kg^?1, respectively. Also, the Co₃O₄/GO has the lowest amount of resistance compared to other electrodes. Nearly constant efficiency at 104% after 1000 cycles indicates that the nanocomposite has excellent cyclic stability. The proper electrochemical efficiency of the nanocomposite corresponds to the synergistic effect on the composition.     

Effect of vegetative bed on flow structure through a pool-riffle morphology

Natural habitats are created and developed through pool-riffle sequences in rivers, while vegetation cover could play a critical role in the sediment transfer and its quantity and quality. In this study, the effect of vegetation cover on the flow structure in a pool-riffle sequence is investigated in a laboratory flume under bed formation to compare with non-vegetated cover. In this context, instantaneous point velocities were measured by ADV to determine averaged velocity, shear velocity, root mean square velocity, friction factor, Reynolds shear stress and turbulence intensities. Results showed that the vegetation cover increases the thickness of the wall law. Meanwhile, the length of the flow separation zone in the vegetated bedform is more than in the non-vegetated bedform. Variation in roughness coefficients may cause a new boundary layer in which local flow velocities decrease. In both cases (vegetated and non-vegetated bedforms), the momentum is mostly transferred by ejection and sweep phenomena between flow and bedform.     

冷轧带钢切边圆盘剪装置的优化与改进

针对冷轧带钢切边后产生的边部梗压印缺陷,结合切边圆盘剪的剪切原理,设计了一种圆盘剪复合衬套,其采用100Cr钢质内圈和MC尼龙外圈复合结构组成,取代原纯钢质衬套,使圆盘剪在剪切带钢过程中由钢性接触转变为弹性接触,从而避免了带钢边部梗压印缺陷的产生,提高了切边质量与剪切里程数,降低了圆盘剪备件成本,提高了生产效率。     

Structural,microstructural and electrochemical studies on LiMn2-x(GdAl)xO4 with spinel structure as cathode material for Li-ion batteries

Gd and Al co-doped LiMn_2-x(GdAl)_xO₄ (x?=?0, 0.01, 0.02, 0.03, 0.04 and 0.05) materials with spinel structure were synthesized by sol–gel method. Powder X-ray diffraction results confirm the formation of cubic spinel structure and average particle sizes are found to be between 80 and 110?nm from FE-SEM and TEM analysis. Decrease in peak potential difference as a function of doping in Cyclic Voltammetry results establishes enhancement in Li⁺ intercalation and de-intercalation. Electrochemical Impedance Spectroscopy (EIS) results showed that accumulation of charges on electrode has improved with doping over pristine samples. At a doping of x?=?0.02 charge transfer resistance values were found to be least. First cycle charge–discharge profiles for LiMn_1.96(GdAl)_0.02O₄ shows 139.2?mAh/g discharge capacity over other doped derivatives and pure LiMn₂O₄ (119.6?mAh/g) in aqueous Li₂SO₄ electrolyte. Doping of x?=?0.02 exhibit good cycling performance with only a total 4% capacity loss after 30 cycles.     

不锈钢电弧铆焊焊点组织及力学性能

采用电弧铆焊的方法对3 mm+5 mm厚的0Cr18Ni9不锈钢钢板采用搭接形式实现连接. 通过优化焊接电流及其作用时间的参数匹配，以期得到最佳的焊点显微组织和力学性能. 采用X射线检测焊点缺陷的存在，使用金相显微镜研究焊点熔深和熔核尺寸的变化，使用电子万能试验机测试焊点的抗剪力. 结果表明，电弧铆焊焊点呈蘑菇状，与基体圆滑过渡，成形良好，无气孔、裂纹等宏观缺陷. 随着第一段和第二段焊接电流的增大，焊点的熔深和熔核尺寸，及焊点抗剪力随之增大. 优化的工艺参数下，熔深尺寸可达4.07 mm，熔核尺寸可达7.73 mm，抗剪力可达23.654 kN，满足生产需求.     

Adsorption behavior and kinetics of H2S on a potassium-promoted hydrotalcite

Adsorption of H₂S and the influence of steam on its adsorption capacity and kinetics were studied on a commercial potassium-promoted hydrotalcite. The sorbent shows a very high cyclic working capacity for H₂S compared to CO₂ and H₂O, even at lower partial pressures and at different operating temperatures ranging between 300 and 500 °C. The operating temperature does not significantly influence the cyclic working capacity for half-cycle times of 30 min. The adsorption mechanism, however, changes at higher temperatures. At lower temperatures (300 °C) a fast adsorption with a fast approach to steady state was observed. At higher operating temperatures, H₂S reacts with the hydrotalcite structure, forming strongly bonded sulfuric species on the sorbent. When using dry regeneration conditions, the first cycles in cyclic operation at higher temperatures show a significantly higher adsorption of H₂S (especially the first cycle), which cannot be desorbed during regeneration with N₂. After the first fast initial adsorption rate a continuous slow adsorption of H₂S occurs, probably caused by a surface reaction between H₂S and the hydrotalcite structure. This reaction is, however, reversible if steam is used.The adsorption mechanism for H₂S and H₂O was determined using multiple cyclic experiments comparable to previous studies performed for CO₂ and H₂O adsorption. It is evident that the adsorption mechanism developed for CO₂ on the same sorbents is also valid for H₂S, indicating that the developed mechanism is consistent for sour gas adsorption on this type of sorbents. The cyclic working capacity can be significantly increased if steam is used during the regeneration step of the sorbent. The mechanistic model developed for the adsorption of CO₂ and H₂O was successfully validated with more than 160 different TGA experiments. An operating temperature of 400 °C seems to be optimal to achieve a high cyclic working capacity for H₂S, because at higher temperatures the regeneration of the formed sulfuric species seems to be hindered resulting in a significant decrease in the cyclic working capacity.