污泥生物炭中氮硫行为及环境效应研究进展

污泥生物炭中氮硫元素含量高，其氮硫行为和环境效应对全球气候变化的影响不容忽视。以往的研究中，研究者往往以富碳生物炭作为主要研究对象，关注碳对全球气候变化的行为和功效，而对氮硫元素的作用关注不够。本文从原始污泥基本性质到其热解过程，再到生物炭的老化，逐步对污泥生物炭整个生命周期内氮硫的行为及其环境效应研究进行综述，并对未来应注重开展的研究方向进行展望，为生物炭中氮硫元素固定、释放及与之关联的环境效应和温室气体排放控制研究提供理论基础。分析表明，污泥中氮元素含量普遍高于硫元素，且热解过程中氮比硫更容易转移至气相产物。氮硫元素随热解温度的增加，在三相产物中的分配都是炭中持续减少，油中先增后减，气中一直增加。高温（＞800℃）条件下，气相中的氮含量高于固相，而硫元素则仍然主要存在于固相中。污泥生物炭老化及其环境效应研究表明，污泥生物炭氮硫元素与土壤的相互作用及其温室效应问题在今后的研究中应引起重视。     

基于高斯混合隐马尔科夫模型与人工神经网络的紧急换道行为预测方法

为了有效降低因驾驶员紧急换道行为而诱发的交通事故，提高道路交通事故链阻断效率，提出一种基于高斯混合隐马尔科夫模型（GMM-HMM）和人工神经网络（ANN）的紧急换道行为预测方法。首先利用GMM-HMM对车辆行驶状态以及驾驶行为连续观察序列进行换道意图辨识，采用ANN预测下一时段的驾驶行为，再预测换道过程中的横向加速度变化率，从而判断紧急换道的危险程度。驾驶员在环仿真实验及实车实验结果表明，该方法预测避险成功率达92.83%，实验避险成功率达90.32%。该方法能有效地对紧急换道行为进行提前警告与干预。     

加热工艺参数对12%Cr钢晶粒长大行为的影响

研究了不同加热工艺参数下(加热温度1050~1300 ℃,保温时间0.25~24 h)12%Cr超超临界转子钢的奥氏体晶粒长大行为,并通过光学显微镜(OM)观察晶粒尺寸的变化规律,建立晶粒长大数学模型。结果表明:随着加热温度增加,晶粒尺寸逐渐增加,加热温度低于1150 ℃时,晶粒尺寸增加明显,而温度高于1150 ℃后,晶粒尺寸逐渐趋于稳定;随着保温时间的增加,晶粒尺寸逐渐增加,保温时间增加到3 h后,晶粒尺寸增加趋势放缓。采用非线性回归方法和Arrhenius晶粒长大模型,建立了该钢的晶粒长大数学模型。     

Numerical analysis on combustion process and sodium transformation behavior in a 660 MW supercritical face-fired boiler purely burning high sodium content Zhundong coal

CHEMKIN software was used to optimize the reaction mechanism of sodium in flue gas to study the influence of targeted design for purely burning Zhundong (ZD) coal on boiler characteristics. Then, the optimized 32-step elemental reaction was combined with CFD software. An eddy-dissipation concept model considering detailed chemical reactions was used to simulate the transformation behavior of sodium-containing substances. The combustion characteristics of the 660 MW face-fired boiler under various loads were also simulated. The field distribution in the furnace and the migration path of sodium along the track of pulverized coal particles were obtained. The results show that the interference between each burner in the furnace is small at the BMCR load, and the phenomenon of “wind wrapping fire” is distinctly clear. The temperature at furnace outlet is approximately 970.98 °C. At a low load, the combustion in the furnace is stable, and the temperature at the furnace outlet reaches the design value. The sodium present in ZD coal is involved in the reaction after it is released in the form of Na and NaCl. Sodium is present in different forms in the main burner zone, mainly NaCl (67%), NaOH (12%), Na (9%), and Na₂SO₄ (7%). The forms of sodium at the furnace outlet are NaCl (50%), Na₂SO₄ (37%), Na₂Cl₂ (9%) and NaHSO₄ (4%). A small amount of Na₂SO₄ is formed by NaHSO₄ reaction in the main burner zone. It then reacts to form NaSO₄, wherein NaHSO₄ is formed by path 2. Na₂SO₄ is mainly generated in the burnout zone through path 1, and paths 2, 3, and 4 are hardly observed. The findings of this research can provide reference for the design of a purely fired ZD coal boiler and further studies on slagging observed on the heating surface.     

Smelling our appetite? The influence of food odors on congruent appetite,food preferences and intake

We are surrounded by sensory food cues, such as odors, that may trigger (un)conscious decisions and even lead to (over)eating, it is therefore crucial to better understand the effect of food odors on behavioral responses. Food odor exposure has been shown to enhance appetite for food products with similar properties: sensory-specific appetite. This suggests that based on previous encounters with foods, we have learned to detect the nutritional content of foods, through our sense of smell. We investigated the influence of aware exposure of macronutrient-related odors on various measures of eating behavior, in a cross-over intervention study. Thirty two normal-weight healthy and unrestrained Dutch females took part in five test sessions. On each test session, they were exposed to one of five conditions (active smelling of clearly noticeable odors representing food high in carbohydrates, protein, and fat, low in calories, and a no-odor condition for 3-min) and assessed on specific appetite, food preferences and intake. Odor exposure increased congruent appetite after protein-related odor exposure. Similarly, protein-related odor exposure influenced the liking for protein foods and the preference ranking for savory products. However, food intake was not affected by smelling congruent food odors. Together this indicates that exposure to (aware) food odors may mostly influence appetite, but does not impact subsequent food intake. Moreover, appetite seems to be triggered by taste qualities rather than macronutrient information of the food, as signaled by olfactory cues. Future studies should investigate the role of awareness in more detail, to fully understand how odors might be used to steer people towards healthier food choices.     

A miniature triaxial apparatus for investigating the micromechanics of granular soils with in situ X-ray micro-tomography scanning

The development of a miniature triaxial apparatus is presented. In conjunction with an X-ray micro-tomography (termed as X-ray μCT hereafter) facility and advanced image processing techniques, this apparatus can be used for in situ investigation of the micro-scale mechanical behavior of granular soils under shear. The apparatus allows for triaxial testing of a miniature dry sample with a size of \mathrm{8}\hspace{0.17em}\mathrm{mm}\times \mathrm{16}\hspace{0.17em}\mathrm{mm} (diameter \times height). In situ triaxial testing of a 0.4–0.8 mm Leighton Buzzard sand (LBS) under a constant confining pressure of 500 kPa is presented. The evolutions of local porosities (i.e., the porosities of regions associated with individual particles), particle kinematics (i.e., particle translation and particle rotation) of the sample during the shear are quantitatively studied using image processing and analysis techniques. Meanwhile, a novel method is presented to quantify the volumetric strain distribution of the sample based on the results of local porosities and particle tracking. It is found that the sample, with nearly homogenous initial local porosities, starts to exhibit obvious inhomogeneity of local porosities and localization of particle kinematics and volumetric strain around the peak of deviatoric stress. In the post-peak shear stage, large local porosities and volumetric dilation mainly occur in a localized band. The developed triaxial apparatus, in its combined use of X-ray μCT imaging techniques, is a powerful tool to investigate the micro-scale mechanical behavior of granular soils.     

AA7075高强铝合金热冲压流变行为本构模型对比研究

在热冲压过程中,AA7075高强铝合金板料经充分固溶后移入室温模具进行冲压成形并淬火。为表征AA7075铝合金在热冲压工艺中的变形行为,在温度200~480℃、应变速率0.01~10s-1范围内进行了高温拉伸试验。基于Arrhenius类型本构模型、Johnson-Cook模型以及Zerilli-Armstrong模型提出了多种修正本构模型,并应用实验所获流变曲线进行了拟合。提出的修正模型通过将模型参数表示为应变、应变速率及温度相关的多项式函数耦合了应变、应变速率及温度对流变应力的影响,并通过均方误差(MSE)以及相关系数R值对模型流变应力预测准确性进行了评价。结果表明,修正的Johnson-Cook模型能够更加准确的预测AA7075高温流变行为。     

Characterization of the structure and diffusion behavior of calcium alginate gel beads

A simple and novel method using gel shrinkage to indirectly characterize the structure of calcium alginate gel (CAG) beads during the calcium alginate gelation process was presented in this study. The effect of preparation process parameters (gelling cations, bead diameter, and alginate M _w and concentration) on the structure of the CAG bead formation process was thoroughly investigated. It was found that (a) the concentration of the Na⁺ and Ca²⁺ ion in gel bath was found to be the determining factor in the gel structure formation process by regulating the dissociation of alginate and the complexation of the calcium; (b) Na⁺ acts as a competitor with calcium and a screen in the electrostatic repulsion; (c) the effect of beads size below 700 μm on the structure of CAG beads can be neglected; and (d) the sodium alginate concentration has no significant effect on the gel formation process. Furthermore, the diffusion of bovine serum albumin (BSA) was controlled by the density of CAG bead. Consequently, a faster diffusion rate of BSA within the looser structure of beads can be observed. These results are keys to understanding the behavior and performance of beads in their utilization medium. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48923.     

Electrical and mechanical properties of BZT − xBCT lead-free piezoceramics

In this study, lead-free (1 − x)Ba(Zr_0.2Ti_0.8)O₃ − x(Ba_0.7Ca_0.3)TiO₃ compositions are synthesized via conventional solid oxide route, and the ceramics are fabricated with normal sintering in air. The effects of composition fluctuations on dielectric, piezoelectric, and mechanical properties are investigated. The phase structure and the microstructure are analyzed with X-ray diffraction and scanning electron microscopy. The best dielectric and piezoelectric properties of ε_r = 11 207 and d₃₃ = 330 pC/N were obtained for BZT−0.35BCT and BZT−0.5BCT ceramics, respectively. The mechanical behavior—in terms of Vickers hardness and compressive and flexural strengths—was investigated, and the best mechanical behavior was found in the vicinity of the phase transition boundary with x values between 0.5 and 0.6.     

Study of tribological properties of polymer derived ZrB2-SiC ceramics

ZrB₂–SiC composite ceramics with different compositions (20 and 60?vol% ZrB₂–SiC, 20ZS and 60 ZS, respectively) were prepared. Wear tests were conducted on the obtained ceramics in multiple distances using ball-on-flat tribotester. Volume loss and cross-sectional profiles of samples were measured by three–dimensional (3D) profilometer to study the onset of track wear damages. Pressure–depth curves and hardness were measured by indentation to investigate defects produced in the tribo-film by the debris. The debris of 20ZS was found to be joined to the tribo-film and accumulated with distance, shifting from microcrack (＜10,000 cycles) to abrasive wear (50,000 cycles). Compared to 20ZS, lower debris accumulation of 60ZS resulted in better wear resistance, leading to thinner and more stable non-substrate regions for this sample. These differences between both samples basically resulted from different particle sizes. Fine grains were easily pulled out in the experiment, resulting in abrasive wear of the specimen. While transgranular fracture of grains and the pinning led to larger grains with less debris, the damage mode remained transgranular fracture.