Sanierung eines PCE-Schadens in einem makroskopisch oxischen Grundwasserleiter durch Stimulation anaerober dehalogenierender Bakterien

Grundwasser - Eine erfolgreiche biologische In-situ-Sanierung von PCE-kontaminierten Grundwasserleitern erfordert hinreichend reduzierende Bedingungen sowie die Anwesenheit von molekularem...     

隧道中气囊阻漏的工作机理及模型试验研究

近年来,地下隧道工程发展迅速,在建设和使用过程中的突发事件也层出不穷。地下隧道常经过含水丰富的土层或岩层裂隙发育地带,因此容易发生渗漏或者涌水突泥的问题。为减少工程损失,需尽快将涌水区隔离,为进一步的处置争取时间。采用大尺寸橡胶气囊进行隧道挡水,是通过快充而膨胀的气囊与隧道内壁之间产生的摩擦力抵消水压力,将水阻隔在气囊一端,避免涌水面积扩大。本文假设气囊材料不可拉伸,内部气体满足理想气体状态方程,通过分析气囊的受力情况和边界条件,对气囊在充气过程中和一端有外力时的形状和受力特点试验和理论研究,得到气囊受到外压时整体形状和内部气压的理论公式,以及外压与内压的关系,提出气囊阻水的设计计算方法。通过模型试验对变化规律、公式和气囊失稳方式进行了对比分析,研究结果表明,隧道中气囊正常工作需同时满足3个控制条件:(1)一端的外压必须小于气囊的内压;(2)气囊的张拉力必须小于气囊材料的抗拉强度;(3)外荷载推力必须小于气囊与隧道壁之间的最大摩阻力。通过理论研究所得的气囊失效机理和内压增长规律与模型试验所得结果有较高的一致性,研究成果可作为隧道中大尺寸胶囊设计的依据。     

David Godschalk

David R. Godschalk, professor emeritus in the Department of City and Regional Planning at the University of North Carolina, Chapel Hill, passed away in early 2018. In this essay we reflect on Dave’s planning scholarship and practice. We discuss his main contributions in 4 prominent areas. First is the importance of public participation and collaboration for the planning and governance of communities. He argued for democratizing and recasting public participation, with planners working alongside community members coproducing plans and incorporating uncertainty, new information, and different viewpoints. Second is Dave’s focus on the tenets of the comprehensive plan and its core element, the land use plan. In the plan, central principles of livable urban forms and model planning processes can be integrated and translated to practice. With academic collaborators and practitioners he pioneered theoretical and empirical research on what constitutes a high-quality plan, a fundamental question at the heart of planning. Third is his research demonstrating how spatial planning can be used for hazard mitigation and urban resilience. This work forged a new generation of planning academics and practitioners who focused on hazard plans for predisaster mitigation and postdisaster recovery at multiple governmental levels. Finally, fourth is his personal involvement in planning-related institutions that he helped create, lead, or steer. In his various roles as scholar, teacher, mentor, collaborator, supervisor, planning director, and elected official, Dave touched the lives of many who now build on his contributions in creating better communities.     

用金刚石磨头数控加工轴对称非球面光学玻璃透镜

为了提高轴对称非球面透镜的形状精度,降低其精加工成本,用金刚石小磨头在不同的加工参数和数控走刀轨迹条件下对K9光学玻璃透镜进行铣磨实验加工。透镜的轮廓精度用三坐标测量机测量,通过测量的数据点计算非球面透镜的法向轮廓度误差,并用数控加工时磨头的有效切削半径进行补偿。实验结果表明:当数控走刀轨迹为平行精加工和等高精加工时,加工后非球面透镜的面型精度最大轮廓度偏差PV和误差平均值RMS分别为54.48 μm和22.88 μm、98.46 μm和28.88 μm;通过优化金刚石磨头的有效切削半径可以提高非球面透镜加工的面型精度,平行精加工后优化的非球面透镜面型精度PV和RMS值分别为44.52 μm和7.37 μm。      

信息化条件下直升机维修保障人才培训体系

针对目前直升机维修保障力量难以适应信息化作战保障要求的问题,对直升机维修保障人才培训的特点和规律进行研究。介绍信息化条件下直升机维修保障人才培训的新特点,分析当前影响直升机维修保障人才培训效益的主要因素,从5个方面提出了信息化条件下直升机维修保障人才培训体系建设措施。研究结果表明:该体系为直升机专业院校和直升机部队的维修保障人才培训提供了理论依据,能促进直升机维修保障人才培训能力的提高。     

Effect of surface curvature and wettability on nucleation of methane hydrate

Natural gas hydrate nucleation is a complex physical and chemical process that is not well understood presently. In this article, an improved thermodynamic model is proposed to analyze the effects of surface curvature and wettability on methane hydrate nucleation for the first time. The results indicate that methane hydrate nucleation is more difficult on hydrophilic curvature surfaces under the same conditions, with a larger critical nucleation radius and required energy barrier than on hydrophobic surfaces. Furthermore, a convex surface is more favorable for forming methane hydrate under the same conditions than a concave surface. The model's results are critical in elucidating the microscopic mechanism of methane hydrate nucleation and providing a theoretical foundation for developing technologies for strengthening and inhibiting hydrate formation.     

Investigation of Nd3+ incorporation in Ce-rhabdophane: Insight from structural flexibility and occupation mechanism

LnPO₄ · 0.667H₂O rhabdophane has been considered as a potential material for the precipitation of actinides from radioactive waste liquid, owing to its outstanding characteristics of high actinide bearing and easy synthesis in acid solutions. However, a comprehensive understanding of the actinide occupation and the precipitation response of rhabdophane to remove actinides has yet to be established. In this study, the effect of ions concentration and pH values on the detailed precipitation reaction of Ce_xNd_1-xPO₄ · 0.667H₂O rhabdophane in acid solutions are systematically investigated. Some specific issues such as structural distortion and flexibility, and occupation mechanism are discussed by combining with experiments and density functional theory (DFT) calculation. The results reveal that ions concentration and pH values have a significant impact on the crystallization nucleation step before 12 h. The obtained removal rate of Nd³⁺ is more than 99% in pH 1–5 solutions with the ions concentration of 0.05–0.1 mol/L. Moreover, incorporating Nd in CePO₄ · 0.667H₂O rhabdophane will easily result in the lattice distortion in b-axis. DFT calculation and X-ray photoelectron spectroscopy (XPS) results reveal that Nd is preferentially incorporated in nonhydrated site to form a weaker binding energy of NdO₈ polyhedron.     

The effect of monoethylene glycol on the stability of water-in-oil emulsions

It is important from both a strategic and economic standpoint to study the mechanism of formation of water/oil emulsions, to predict their increase of viscosity with respect to that of the crude oil, and to obtain information about the stability vs separation of these substances (since their presence can impair oil processing and distribution). The objective of this work was to ascertain the influence of monoethylene glycol (MEG) on these parameters and its action mechanism. The addition of MEG in different proportions in the oil emulsions significantly changed the flow curve of the emulsion, passing from a quasi-Newtonian one to a shear thinning behaviour. Besides this, when MEG was present at low concentrations, the demulsification process was slow and an increase in concentration made the emulsions more stable than samples containing the same aqueous phase proportion. Under the conditions studied, the addition of MEG did not reduce the quantity of the aqueous phase separated compared to the emulsions free of MEG, but significantly delayed the demulsification process. Rheology provided important information regarding the phase separation process of the aqueous phase in oil phase emulsions, and dynamic testing suggested that the most relevant effect of the addition of MEG is an increase of the emulsion elasticity that can be correlated with the increase in the emulsion stability observed by bottle test and Turbiscan.     

生物质与烟煤混合燃烧特性及动力学分析研究

使用非等温热分析方法研究了生物质(麦秆)和烟煤混合燃烧的反应特性。结果表明,生物质的添加可以降低混合样品的燃烧着火温度和燃烬温度,且混合样品燃烧反应性能随着生物质混合比例的增加而提升;生物质添加质量分数为20%时,煤和生物质混合燃烧协同作用最明显。使用Coats-Redfern(CR)、Flynn-Wall-Ozawa(FWO)和Kissinger-Akahira-Sunose(KAS)动力学模型对混合样品燃烧活化能进行计算,其值在挥发分燃烧阶段随着生物质混合比例的增加而增加,在焦炭燃烧阶段呈现下降趋势;通过对FWO和KAS动力学模型有效性进行分析发现,FWO和KAS模型在描述混合样品燃烧动力学时存在一定的局限性,而采用适宜机理函数的CR模型更适用于描述混合样品的燃烧反应动力学,对燃烧机理的分析也印证了动力学的分析结果。