Mass transfer in polycrystalline ytterbium monosilicate under oxygen potential gradients at high temperatures

Mass transfer in polycrystalline Yb₂SiO₅ wafers with precise composition control was evaluated and analyzed by oxygen permeation experiments at high temperatures using an oxygen tracer. Oxygen permeation proceeded due to mutual grain boundary diffusion of oxide ions and Yb ions without synergistic effects such as acceleration or suppression. The oxygen shielding properties of Yb₂SiO₅ were compared with those of the other line compounds such as Yb₂Si₂O₇ and Al₂O₃ based on the determined mass transfer parameters. It was found that the more preferentially an oxide ion diffuses in the grain boundary compared to the interior of the grain, the greater the effect of suppressing the movement of the oxide ion by applying an oxygen potential gradient becomes.     

Exploring the relationship between the physical properties of activated carbon catalysts and their efficiency in catalyzing hydrogen iodide decomposition to produce hydrogen

Using simple and efficient methods to synthesize biological activated carbon catalysts (ACCs) with the decomposition of hydrogen iodide (HI) in the sulfur-iodine cycle as a typical reaction is urgently needed for the commercialization of hydrogen energy production and development. In this study, a series of ACCs with different specific surface areas (SSAs) and pore structures are prepared by comparing and controlling the changes in carbonization and activation methods of activated carbon (AC) preparation process. Hierarchical porous AC with larger SSA has higher HI decomposition efficiency. The representative samples H240H1h and H240C4h are hierarchical porous ACCs with 48.96% and 46.88% micropores, respectively, and have the highest catalytic activity in the entire series. The nitrogen adsorption and desorption curve is combined with pore size distribution data and analyzed using the capillary aggregation (Kelvin) and monolayer adsorption (Langmuir) theories. And ACC pore grading coefficient—which can improve data visualization—is introduced.     

Clustering adaptive canonical correlations for high-dimensional multi-modal data

Multi-modal canonical correlation analysis (MCCA) is an important joint dimension reduction method and has been widely applied to clustering tasks of multi-modal data. MCCA-based clustering is usually dimension reduction of high-dimensional data followed by clustering of low-dimensional data. However, the two-stage clustering is difficult to ensure the adaptability of dimension reduction and clustering, which will affect the final clustering performance. To solve the issue, we propose a novel clustering adaptive multi-modal canonical correlations (CAMCCs) method, which constructs a unified optimization model of multi-modal correlation learning and clustering. The method not only realizes discriminant learning of correlation projection directions under unsupervised cases, but also is able to directly obtain class labels of multi-modal data. Additionally, the method also realizes out-of-sample extension in class labels. Solutions of CAMCCs are optimized by an iterative way, and we analyze its convergence. Extensive experimental results on various datasets have demonstrated the effectiveness of the method.     

对称消声器传递损失测量及误差修正

为了提高对称消声器传递损失的测量效率，基于声学理论分析，提出了一种单负载法传递损失计算模型。针对反射系数较大的吸声末端，导致该方法在实际测量中存在较大误差的问题，推导出了一种能够消除测试管道末端反射声波在上、下游形成多次反射的修正公式。通过自制阻抗管进行试验测试，结果表明：在末端声学负载吸声性能良好的情况下，单负载法传递损失计算模型能够精确计算出对称消声器的传递损失；修正公式能够有效地消除末端负载所引起的反射波对传递损失计算的影响，降低对末端声学负载吸声性能的要求，保证单负载传递损失计算模型的适用性。     

结构参数对电厂翅片管散热器动态特性的影响

散热器经常处于变化的工作条件中,研究散热器的动态特性有助于改善间接空冷系统的安全和经济运行,而散热器的结构参数会影响其动态特性。根据能量守恒建立了散热器空气、管壁和循环水的热平衡偏微分方程,采用改进欧拉法对偏微分方程组进行求解。以迎面风速阶跃变化为典型工况,研究了换热面积、换热系数和工质体积对散热器动态特性的影响。结果如下:当空气侧换热面积增加时,散热器换热量增大,两个稳态之间的空气出口温度差值不变,循环水出口温度差值增加,空气侧响应时间增加,循环水侧响应时间不变。当循环水侧换热面积增加时,散热器换热量增大,两个稳态之间的空气和循环水出口温度差值不变,空气侧和循环水侧的响应时间也不变。换热系数变化时,散热器动态过程的变化规律与换热面积变化时类似。空气侧工质体积变化对散热器动态特性没有影响。循环水侧工质体积增大会使得动态响应时间变长。     

链条炉运行参数对燃烧及NOx排放的影响

通过数值模拟的方法研究了过量空气系数、配风方式、空气预热温度和炉排转速等运行参数对床层燃烧和氮氧化物排放特性的影响。研究结果表明:过量空气系数增大可加快床层整体反应速率,缩短反应区长度,增大床层表面氮氧化物质量浓度;合理推迟配风有利于扩展反应区整体长度,充分利用整个炉排;适当降低炉排转速有利于提高煤着火及前期反应速率,稍缩短总体反应区间;提高空气预热温度有利于煤着火和前期反应速率的提高,且有利于煤的燃尽。     

Estimation of Antenna Correlation Coefficient of N-Port Lossy MIMO Array

This paper proposes a simple yet accurate method for estimating the antenna correlation coefficient (ACC) of a high-order multiple-input multiple-output (MIMO) antenna. The conventional method employed to obtain the ACC from three-dimensional radiation patterns is costly and difficult to measure. An alternate method is to use the S-parameters, which can be easily measured using a network analyzer. However, this method assumes that the antennas are highly efficient, and it is therefore not suitable for lossy MIMO antenna arrays. To overcome this limitation, we define and utilize the non-coupled radiation efficiency in the S-parameter-based ACC formula. The accuracy of the proposed method is verified by the simulation results of a 4-port highly coupled lossy MIMO array. Further, the proposed method can be applied to N-port arrays by expanding the calculation matrix.     

Lubricating and physico-chemical properties of CI- 4 plus engine oil dispersed with surface modified multi-walled carbon nanotubes

This paper studies the effect of surface modification of multiwall carbon nanotubes (MWCNTs) prior to dispersion in engine oil to improve the tribological properties. The MWCNTs are stabilised in the lubricant with two different surfactants cetrimonium bromide (CTAB) and sorbitan monooleate (SPAN 80) and the effect of surfactants on the tribological properties has been studied. Pristine and surface modified MWCNTs in weight per cent range of 0·5% are dispersed in CI4 plus diesel engine oil. The foaming tendency and other physico-chemical properties of test lubricant have been studied to investigate the effect of nano materials and surfactants. The anti-wear and anti-friction properties are tested on a four ball wear tester and the comparison is made to assess the relative performance of pristine MWCNTs over surface modified MWCNTs. A strong influence of the surface modification technique is found on lubricating and physico-chemical properties. Both CTAB and SPAN 80 could keep the MWCNTs stable in the lubricant without compromising the foaming tendency of lubricant and other physico-chemical properties. The friction and wear characteristics of lubricants have improved with the dispersion of surface modified MWCNTs while there is no improvement in the properties of lubricant dispersed with pristine MWCNTs.     

Inorganic thermoelectric materials: A review

Thermoelectric generator, which converts heat into electrical energy, has great potential to power portable devices. Nevertheless, the efficiency of a thermoelectric generator suffers due to inefficient thermoelectric material performance. In the last two decades, the performance of inorganic thermoelectric materials has been significantly advanced through rigorous efforts and novel techniques. In this review, major issues and recent advancements that are associated with the efficiency of inorganic thermoelectric materials are encapsulated. In addition, miscellaneous optimization strategies, such as band engineering, energy filtering, modulation doping, and low dimensional materials to improve the performance of inorganic thermoelectric materials are reported. The methodological reviews and analyses showed that all these techniques have significantly enhanced the Seebeck coefficient, electrical conductivity, and reduced the thermal conductivity, consequently, improved ZT value to 2.42, 2.6, and 1.85 for near-room, medium, and high temperature inorganic thermoelectric material, respectively. Moreover, this review also focuses on the performance of silicon nanowires and their common fabrication techniques, which have the potential for thermoelectric power generation. Finally, the key outcomes along with future directions from this review are discussed at the end of this article.