Function mechanism of Y2O3 additive in silicon powder nitridation

Effect of sole Y₂O₃ additive on the nitridation behavior of silicon powder was systematically studied using thermo gravimetry, differential thermal analysis, particle size analysis, X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscope and thermodynamic analysis in this paper. The thermo gravimetry results showed that Y₂O₃ additive can significantly decrease the initial nitriding temperature and increase the nitriding rate. This phenomenon can be attributed to the much lower reaction temperature of the silica film and Y₂O₃ additive than that of the silica film and silicon. In addition, Y₂O₃ additive has little effect on the nitridation of silicon powder at 1300°C. However, it can obviously enhance the nitridation of silicon powder and the formation of β-Si₃N₄ at 1400°C, which is evidenced by the fact that the overall conversion increases from 58.1% to 100% and the fraction of β-Si₃N₄ in generated Si₃N₄ increases from 7.9% to 68.2% with increasing the content of Y₂O₃ additive from 0 to 10 wt%.     

Integrated processing of plant-derived waste to produce value-added products based on the biorefinery concept

BackgroundPlant-derived wastes from agriculture, processing, distribution, and retail are generated in large quantities. The majority of the wastes are underutilized and may cause severe environmental problems if not properly handled. The plant-derived wastes are usually rich in lignocellulose and other valuable compounds including protein, fat, sugar, and phytochemicals. Valorization of these compounds in food waste not only reduces environmental concerns but also improves sustainability and economic competitiveness of agro-food industries.Scope and approachThis review paper first discussed different phases of the biorefinery concepts and their associated applications, and then introduced recent advances in the integrated processing of plant-derived waste for producing various value-added products. Finally, techno-economic, environmental, and social assessments along with relevant policies were introduced and discussed.Key findings and conclusionsDuring the past ten years, research attentions focused on integrated utilization of plant-derived waste to produce various products have flourished. Compared to production of a single component for food waste valorization, integrated processing of food waste via a combination of different novel technologies to produce multiple products based on a biorefinery concept has significant advantages, including full utilization of feedstocks, minimization of waste generation during processing, synergy effects of different technologies, and diversification of the revenues by covering multiple markets. With the rationale design of biorefinery processes, underutilized plant-based wastes can be valuable resources for the sustainable production of food, chemicals, and biofuels. However, detailed economic, environmental, and social analyses for the biorefinery process are still needed in the future.     

Finite element analyses of slope stability problems using non-associated plasticity

In recent years, finite element analyses have increasingly been utilized for slope stability problems. In comparison to limit equilibrium methods, numerical analyses do not require any definition of the failure mechanism a priori and enable the determination of the safety level more accurately. The paper compares the performances of strength reduction finite element analysis (SRFEA) with finite element limit analysis (FELA), whereby the focus is related to non-associated plasticity. Displacement-based finite element analyses using a strength reduction technique suffer from numerical instabilities when using non-associated plasticity, especially when dealing with high friction angles but moderate dilatancy angles. The FELA on the other hand provides rigorous upper and lower bounds of the factor of safety (FoS) but is restricted to associated flow rules. Suggestions to overcome this problem, proposed by Davis (1968), lead to conservative FoSs; therefore, an enhanced procedure has been investigated. When using the modified approach, both the SRFEA and the FELA provide very similar results. Further studies highlight the advantages of using an adaptive mesh refinement to determine FoSs. Additionally, it is shown that the initial stress field does not affect the FoS when using a Mohr-Coulomb failure criterion.     

When ‘knowing what’ is not enough: Role of organised simulations for developing effective practice

A decade on from the Rethinking Project Management (PM) network, concerns about the relevance gap continue with a number of multinationals looking explicitly to alternative strategies and forms of PM staff development. The literature is light on how project simulations can help the development of experienced managers as reflective experts. Few have examined the link between intended learning outcomes and real-time performance. Posing the question of “how easily is knowledge developed in the classroom transformed into effective practice?” the paper presents a chronological account of a 3-day simulated project by 25 experienced managers. Despite their prior experience and learning from shared problem-solving and structured reflections, participants struggled to deliver their projects as planned. Analysis referencing the knowledge epistemology and ambidexterity literatures yielded a number of design improvement opportunities and the insight that closing the knowing-doing gap requires courses to incorporate the ‘soft’ perceptual and attitudinal aspects underlying why people fail to convert their learning into effective practice.     

功能追随空间：多尺度层级网络塑造的城市中心

城市商业功能的分布与道路空间结构息息相关。本文以北京内城为例,应用空间句法模型在城市和街区两个尺度上分析了商业功能的聚集和演变规律。其中在城市尺度基于80年跨度中四个时间节点的商业分布数据分析了10个商业中心,在街区尺度上基于2005和2015年的实地调研的商铺数量,分析了前门、东四和西四三个中心区内的各街道段上的商业分布受城市和局域层级网络影响的程度。结论验证了空间句法参数能够有效地在街道精度上分析商铺数量,但各案例街区受两种网络影响程度差异较大。     

基于金属基复合材料的硅通孔热应力仿真分析

硅通孔(TSV)技术是三维集成电路中的关键技术,对信号传输以及热量的传导起到关键的作用,其热可靠性的问题一直都是研究热点。基于Comsol Mulitiphsics平台,通过有限元仿真分析,研究了金属基复合材料对TSV热应力的影响。并进一步研究了在不同通孔直径以及不同TSV高度下,碳纳米管(CNTs)、碳纳米管铝(CNTs/Al)以及碳纳米纤维铜(CNFs/Cu)等复合材料和传统金属材料的等效热应力情况。结果表明:与传统金属材料相比,金属基复合材料CNTs/Al以及CNFs/Cu均能有效降低TSV的热应力,提高TSV的热可靠性;并且对于CNTs含量不同的金属基复合材料,其TSV的等效热应力也会有所不同,需综合考虑合理选择CNTs的含量。     

带缓冲区且产品保修的设备预防性维护建模

论文考虑的是一个完美的生产系统,即生产系统所生产的产品均没有质量问题。为提高设备的可靠性,调整市场需求,提出带缓冲区的设备预防性维护优化建模方法。已经出售的产品,顾客在使用过程中可能会出现故障,基于这个情况,在保修期内会予以免费维修。找出生产系统的运行时间(T)和缓冲区库存量(S),以此为决策变量建立期望成本模型。在此基础上,构造求解最优策略的算法。通过数值算例演示了该模型,通过灵敏度分析确定了最优策略和相关参数的关系。     

Analysis of flame structure using detailed chemistry and applicability of flamelet/progress variable model in the laminar counter-flow diffusion flames of pulverized coals

Pulverized coal is still found in many practical devices even though it is recognized as “dirty fuel” because of its CO₂ and pollutant emissions. To overcome this problem, advanced coal utilization technologies have been developed using numerical simulations. In this study, the structures of the laminar counter-flow diffusion flames of pulverized coals were investigated by performing simulations based on detailed chemistry. The high-temperature region became narrower as the coal/air ratio increased, because of the departure from the stoichiometric mixture and local quenching by the heat transfer between the gas and solid phases. Further, the applicability of the flamelet/progress-variable (FPV) model was investigated through a priori and a posteriori tests. The a priori test confirmed that the FPV model is capable of reproducing the numerical solutions obtained using the detailed chemistry, including the mass fractions of minor species. In the a posteriori test, there was a slight difference between the FPV model and detailed chemistry results due to overestimation of the progress of the chemical reactions. Given the sufficiently high accuracy of the FPV model in various numerical conditions, it can be concluded that the extended FPV model has potential for use in turbulent coal combustion simulations.     

Multistage homogenization process of aluminum alloy 2618

Single-, two-, and three-stage homogenization treatments of heat-resistant alloy 2618 were conducted in this study. Results reveal a low melting point Al₂CuMg phase and high melting point Al₂Cu phase in the as-cast aluminum alloy 2618. After single-stage homogenization at 495 °C for 10 h, the Al₂CuMg phase dissolves completely, but the Al₂Cu phase cannot be completely dissolved even once the homogenization time is prolonged to 18 h. After the alloy 2618 are homogenized using two stages: 495 °C for 10 h and 520 °C for 8 h, a portion of the Al₂Cu phase remains in the alloy. The Al₂Cu phase remains undissolved even after prolonged time. After the two-stage homogenization treatment at 495 °C for 10 h and 540 °C for 5 h, the high melting point Al₂Cu phase completely dissolves but overburn occurs. After the alloy 2618 are homogenized using three stages at 495 °C for 10 h, 520 °C for 5 h, and 540 °C for 3 h, the Al₂Cu phase completely dissolves and no overburn is detected. The three-stage homogenization treatment is an effective method for dissolving the high melting point Al₂Cu phase in the alloy 2618 and increasing their overburn temperature and solid solution temperature.     

METCAL 在 Co3O4 制备工艺设计中的应用

采用 METCAL 软件创建计算模型，对沉淀 - 热分解法制备四氧化三钴材料的工艺进行了模拟，并简要介绍了过程模拟的步骤和思路。通过对工艺流程的模拟计算，得到了直观的物流分配走向、金属平衡和热平衡数据等，为四氧化三钴材料制备工艺工程设计提供了基础数据支撑。