Microstructural evidence for short-circuit oxygen diffusion paths in the oxidation of a dilute Ni-Cr alloy

A comparative study of high-temperature oxidation of Ni containing 1 at.% Cr and pure Ni was carried out. Instead of the conventional kinetics study using thermogravimetry, a microlithographic marker experiment was designed. Observation of the markers using cross-sectional TEM and SEM has revealed striking differences in the scale morphology, microstructures, and oxidation mechanisms between pure Ni and the Cr-doped Ni substrates. In particular, the results suggest that a small addition of Cr promotes significant inward transport of oxygen. Marker experiments revealed that NiO grown on pure Ni is wholly attributable to outward-cation diffusion. In contrast, NiO grown on Ni–1 at.% Cr exhibited formation of a substantial inner layer having a submicron grain size, established by the markers to have formed from oxygen ingress. For pure Ni, voids were observed to be distributed only within oxide grains. In contrast, for Ni containing 1 at.% Cr, elongated pores formed extensively along oxide-grain boundaries. Formation of new fine-grain oxide in these pores was observed to have sometimes completely resealed the void. It is, therefore, proposed that the transport of oxygen in the case of oxide scale grown on Ni–1 at.% Cr occurs via voids (pores) formed by vacancy coalescence at the grain boundaries.     

A new short-path distillation system applied to the reduction of cholesterol in butter and lard

A molecular distillation plant, built particularly to increase the separation efficiency and to obtain safer working conditions, was tested to remove cholesterol from anhydrous butter and lard. A preliminary experiment was carried out with butter to evaluate the fractionation obtained at temperatures between 190 and 250°C and residual pressures between 10⁻³ and 10⁻⁴ torr. A second experiment was carried out at 185°C and at the maximum operational vacuum, evaluating the fractionation achieved within a time scale between 30 and 180 min. Cholesterol was almost completely removed during the second hour with minimal loss of low-molecular weight triglycerides. An experiment was carried out with lard at 250°C and maximum achievable operational vacuum (10⁻⁴ Torr), lasting approximately 6 h, and cholesterol was removed almost completely during the second hour without significant modifications in the triglyceride composition. This situation remained constant throughout the duration of the test.     

Synthesis of Dimethyl Carbonate from Methanol and Carbon dioxide using Potassium Methoxide as Catalyst under Mild Conditions

Pd-supported on WO₃–ZrO₂ (W/Zr atomic ratio=0.2) calcined at 1073 K was found to be highly active and selective for gas-phase oxidation of ethylene to acetic acid in the presence of water at 423 K and 0.6 MPa. Contact time dependence demonstrated that acetic acid is formed via acetaldehyde formed by a Wacker-type reaction, not through ethanol by hydration of ethylene.     

分子蒸馏过程模型化研究进展

介绍了分子蒸馏基本原理和常用分子蒸馏设备 ,系统地对分子蒸馏过程模型化的研究进展情况进行了叙述 ,重点介绍了蒸发系数法、液体内部传质传热和蒸馏区惰性气体压力对分子蒸馏的影响等方面的研究结果 ,并对其进行了评述 ,同时对分子蒸馏过程研究的进一步发展提出了一些展望。     

Synthesis of Sn-Incorporated Folded Sheets Mesoporous Materials (Sn-FSM-16)

Sn-incorporated folded sheets mesoporous materials (Sn-FSM-16) with various contents of Sn were synthesized by using a mixture of water glass, SnCl₄ and NaOH as starting materials. Hexadecyltrimethyl-ammonium chloride (surfactant) was used to intercalate into the layered silicate. The reaction process was followed by measurements of XRD patterns of intermediates. The Sn-FSM-16 was formed via the following mechanism: (1) layered silicates such as - - and -Na₂Si₂O₅ were formed as intermediates by the calcination of the mixture of the starting materials; (2) the surfactant was intercalated into the layered silicates; (3) the surfactant-silicate complex with hexagonal structure was obtained as a precursor of Sn-FSM-16; (4) the precursor was calcined to decompose the surfactant in the interlayer and was changed to Sn-FSM-16. The structural aspect of Sn in Sn-FSM-16 was studied by XPS profiles of Sn 3d _5/2 and Si_2p, ²⁹ Si MAS NMR and FTIR. The content of Sn in Sn-FSM increased with increasing concentrations of both Sn and NaOH in the starting materials. The surface area of Sn-FSM-16 decreased with an increase of Sn content in Sn-FSM (1160–620 m²/g).     

低空复杂环境下基于采样空间约减的无人机在线航迹规划算法

针对低空复杂环境下障碍物密集且类型多样、带有多通道并存在不确定信息的无人机在线航迹规划问题,为了减少碰撞检测次数,提高航迹搜索速度,降低航迹代价,提出一种基于采样空间约减的无人机在线航迹规划算法. 算法通过引入代价模型,提出约减域逐步构造方法,引导规划树快速有效扩展,改善了基于动态域的快速拓展随机树（Dynamic domain rapidly-exploring random tree,DDRRT） 算法中存在的采样空间过度约减问题. 算法通过密度划分索引的方法逐步构建多棵Kd 树（K-dimensional tree）并采用多近邻节点搜索方法,加快了近邻树节点搜索速度. 仿真实验结果表明,与DDRRT方法相比,该方法在保证对采样空间约减合理性的同时,提高了航迹规划效率和通道内的寻路能力.     

基于线性时序逻辑的最优巡回路径规划

基于线性时序逻辑(Linear temporal logic, LTL)的路径规划方法中, 多点巡回路径规划问题尚无有效解决方案. 为了在道路网络中实现最优巡回监测, 提出了基于LTL的最优巡回路径规划方法. 首先, 将环境建模成一个切换系统, 用LTL语言描述包含多个巡回点和障碍物的任务需求; 接着, 利用循环移位法构建能够融合任务需求和环境模型的扩展乘机自动机, 以建立路径信息完整的网络拓扑; 最后, 采用基于迪科斯彻法的最优综合算法搜索扩展乘机自动机网络上的最优路径, 从而获得能够满足复杂任务需求的最优巡回路径. 仿真结果表明, 该方法能够有效实现最优巡回路径规划.     

多层水平气流带式干燥机的数学模型

根据干燥传质传热学原理和干燥动力学特性，建立了水平气流带式干燥机干燥过程的数学模型。该模型可以预测干燥机合理的通风道高度、带翻转最佳时间和热风风速等。为优化多层带式干燥机的结构或设计新的水平气流带式干燥机提供了理论依据。     

路径长度受限的随机需求VRP的模型和算法

路径长度受限的随机需求VRP在生产、生活中有着广泛的应用。给出了路径长度受限的随机需求VRP问题的线性整数规划模型,在不允许部分服务和仅能服务失败一次的策略下设计了一个启发式算法。该算法以离散优化中广泛应用的扫描算法为基础生成服务的一个初始可行方案,然后利用模拟退火算法改进得到近似最优解。对需求为二项分布的50个结点、1个服务中心的问题进行了数值试验,数值结果表明该算法对求解路径长度受限的随机需求VRP是有效的。     

Coverage path planning for eddy current inspection on complex aeronautical parts

Non-destructive testing (NDT) plays a critical role in controlling the structural integrity (therefore the quality) of aeronautical parts, during fabrication as well as during maintenance. Eddy current (EC) testing is one of the most used NDT techniques in the aerospace industry. However, EC testing is still mainly performed by human operators and reliability as well as repeatability is not always guaranteed. To solve these issues, automating this NDT technique with a robotic system is investigated. In this paper, an EC probe equipped with a passive compliant system is assumed to be attached to the end-effector of a 6-DOF manipulator arm to carry on the inspection. Then, assuming that a 3D model of the inspected part is known a priori, a coverage path planning method using a zigzag (or rastering) pattern adapted to EC testing on aeronautical structures with a complex geometry is proposed. To reach this objective, the approach adopted in this work is to adapt existing coverage path planning techniques based on a “divide-and-conquer” strategy used for spraying applications to EC inspection. More precisely, three successive segmentations are applied to the surface to be inspected so that consistent rastering paths can be generated. Simulation results are shown for a complex part of an aeronautical structure to demonstrate the efficiency of the proposed method.