Thermal decomposition of energetic materials 12. Infrared spectral and rapid thermolysis studies of azide-containing monomers and polymers

The IR spectra of the monomers and homopolymers of glycidyl azide (GAP), 3-azidomethyl-3-methyloxetane (AMMO), 3,3-bis(azidomethyl)oxetane (BAMO), 3-azidooxetane (AZOX), and 3-(2,3-diazidopropoxymethyl)-3-methyloxetane (DAPMMO) were assigned. Rapid-scanning Fourier transform infrared spectroscopy (10 scans s⁻¹) was used to characterize the slow (5K min⁻¹) and rapid thermolysis (50–255K s⁻¹) of these compounds. The azide group decomposes before the polymer backbone does. However, once decomposed the products are essentially a mixture of those expected of low-membered cyclic ethers and methyl azide. The gaseous decomposition product concentrations are strikingly insensitive to the applied pressure (1–1000 psi Ar) and to the heating rate (50–255K s⁻¹). HCN is the dominant IR active product in all cases except for AMMO monomer, where CO is more abundant. AMMO polymer is the most thermally stable of the polymers.     

Rate and oxygen activity oscillations during hydrogen oxidation on nickel films in a CSTR

The catalytic oxidation of hydrogen on polycrystalline nickel films was studied in a CSTR at 510-681°K and atmospheric pressure. The technique of Solid Electrolyte Potentiometry (SEP) was used to monitor the thermodynamic activity of oxygen adsorbed on the catalyst surface. To this end the reaction was studied in an yttria-stabilized zirconia solid electrolyte cell. Both steady state kinetics and potentiometric results indicate formation and reduction of a surface nickel oxide. In a certain range of temperature and gas composition sustained oscillatory phenomena were observed on both the reaction rate and the surface oxygen activity. A dynamic model of six differential equations that takes into account transient changes of the gas phase concentration of H₂, O₂ and H₂O as well as of the surface coverage of adsorbed hydrogen, oxygen and nickel oxide has been developed. The model explains quantitatively the stable steady state kinetic and SEP results. The same model predicts oscillatory behavior and explains qualitatively the observed unsteady state phenomena.     

In situ uv visible reflectance spectroscopic investigation of the nickel electrode-alkaline solution interface

An in situ uv visible reflectance spectroscopic technique is used to investigate the nickel electrode-alkaline solution interface. It is shown that by recording the change in relative reflectivity of the surface vs the potential applied to the electrode, at various fixed wavelengths, it is possible to get the spectra of superficial layers.Reflection-absorption spectra were thus obtained respectively for the hydroxide αNi(OH)₂ (two maxima at 360 and 500 nm) and the oxyhydroxide NiOOH (broad band with a maximum at 500–550 nm), providing new insights concerning the reversibility of some of the electrochemical processes which occur on the electrode surface when varying the potential.     

永磁同步电机脉振高频电压注入转子位置检测

永磁同步电机的转子位置检测精度直接决定了电机能否平滑起动,为提高转子位置检测精度,提出了基于脉振高频电压注入的表贴式永磁同步电机转子位置检测方法。向永磁同步电机定子绕组中注入脉振高频电压信号,通过电机d、q轴磁路饱和程度的差异,实现永磁同步电机转子初始位置的检测。实验结果表明提出方法的转子位置检测精度高,适用于永磁同步电机的无传感器起动及低转速稳态运行。     

Ultrafiltration cell for sorption and biodegradation experiments

The knowledge about sorption and biodegradation of trace organics in soils and sediments of low organic carbon content, such as ground water aquifers, is still meagre. In an attempt to develop a tool to study mechanisms of interactions between low-molecular weight compounds, bacteria, organic polymers and clay minerals, an ultrafiltration membrane cell was designed to be operated either in batch or continuous flow mode. The cell and its maintenance are described, and its performance illustrated by experiments with p-chloroaniline (PCA) in suspension with a microbial polysaccharide and a bentonite clay. PCA at a concentration of about 50 μgl⁻¹ demonstrated sorption only to bentonite, and only after protonation. The reproducibility of the experiments was high resulting in a minimal detectable sorption of PCA of 0.56%. The high sensitivity, reproducibility and replicability of this cell approach are particularly applicable to the current efforts to gain a better understanding of sorption and biodegradation processes in the saturated subsurface.     

Connectivity preservation for multi-agent rendezvous with link failure

This paper proposes a new connectivity-preserving protocol in terms of rectangle-like regions. The protocol consists of a set of distributed control rules; their working together guarantees the network connectivity as well as rendezvous of a discrete-time multi-agent system. It is assumed that all agents share a common minimum sensing radius, but the information exchange may suffer from link failure and recovery. Consequently, the interaction topology is in fact directed and time-varying. By rigorous mathematical arguments, we show the effectiveness and robustness of the protocol in the presence of alignment errors in local coordinate orientations of agents and measurement errors in relative positions of neighbors. We also present simulations to demonstrate the effectiveness of the theoretical results.     

Nd:YAG laser weldability and mechanical properties of AZ31 magnesium alloy butt joints

Laser welding process using a Nd:YAG laser of maximum power of 2 kW was investigated and reported. Magnesium alloy AZ31 sheets with thickness of 3.3 mm have been butt welded with Helium and Argon used as shielding gases. The effect of processing parameters including laser power, welding speed, focal point position, nozzle configuration and protection gas flow was researched. Microstructure and mechanical properties of butt joints welded without filler were studied using optical microscopy, morphological analysis and mechanical tests (tensile, hardness). The first phase of experimental tests consisted in penetration tests (bead on plate) with the aim of identify the range of input parameters. In the second phase butt welding tests were performed in order to determine the optimal conditions. Tensile tests were realized using extensometers and an optical system based on digital image correlation techniques for acquisition and analysis of local deformation. Static tensile tests revealed an increase in the yield strength of all welded specimen in relation to the not welded material. Morphological analysis and mechanical characterization showed a threshold of heat input value below which, even when there is sufficient irradiance, the ultimate tensile strength and the elongation to fracture of the joint decade heavily. The local strain analysis revealed that the fracture occurs due to localization of deformation on weld bead as a result of defects on the surface of the bead. Metallographic analysis of cross-sections did not show defects like porosity, inclusions and cracks, within the weld bead.     

引入特征交互的红外与可见光图像自适应融合北大核心CSCD

在图像融合领域,现有的基于卷积神经网络(CNN)或Transformer架构的方法存在两个局限性:首先,浅层纹理特征与深层语义特征之间无法有效聚合;其次,红外与可见光特征的权重比例无法自适应变化。本文提出一种引入特征交互的红外与可见光图像自适应融合方法。首先,构建一种基于Transformer的特征交互模块,聚合跨尺度特征信息,增强特征表达能力。其次,设计一种融合模块,自适应地调整特征权重比例。所提出的融合方法通过两阶段训练策略完成。第一个阶段,应用创新的特征交互概念训练编码器,增强特征表达,重建特征图像。第二个阶段,基于设计的权重自适应调整模块训练红外与可见光特征融合任务。公开数据集的实验结果表明,与现有方法相比,本方法在主观和客观的评价方面均优于其他典型方法。     

准分子激光电化学刻蚀硅的刻蚀质量研究

为了解决现有硅刻蚀工艺中存在的刻蚀质量等问题,采用激光加工技术和电化学加工技术相结合的工艺对硅进行了刻蚀,研究了该复合工艺的工艺特性。实验中采用248nm-KrF准分子激光作光源聚焦照射浸在KOH溶液中的阳极n-Si上,实现激光诱导电化学刻蚀。在实验的基础上,研究了激光电化学刻蚀Si的刻蚀孔的基本形貌,并对横向刻蚀和背面冲击等质量问题进行了分析。结果表明,该工艺刻蚀的孔表面质量好、垂直度高;解决了碱液中Si各向异性刻蚀的自停止问题,具有加工大深宽比微结构的能力;也具有不需光刻显影就能进行图形加工的优越性。