Effect of process parameters on microstructure and properties of laser welded joints of aluminum/steel with Ni/Cu interlayer

The effects of laser parameters and interlayer material on the microstructure and properties of the welded joint between 6061 aluminum alloy and stainless steel were studied. The results show that the density and microstructure of the welded joint can be optimized by changing the laser power with 0.05 mm Cu foil and 0.1 mm Ni foil as interlayer. A large number of new Cu–Al binary phases were found near the aluminum alloy, which effectively inhibited the formation of the binary brittle phase of Fe–Al. The maximum shear force of 1350.96 N was obtained with laser power of 2200 W. The shear force of the welded joint increased to 1754.73 N when the thickness of the Cu foil thickness changed to 0.02 mm.     

Characterization,Removal and Evaluation of Oxide Film in the Diffusion Bonding of Zr55Cu30Ni5Al10 Bulk Metallic Glass

The composition of oxide film of ZrssCu3oNi5Al10 bulk metallic glass was identified by X-ray photoelectron spectroscopy. In addition, the relatively sound joints of bulk metallic glass without macroscopic deformation were obtained by removing the oxide film before diffusion bonding. The joint interfaces were observed by scanning electron microscopy and atomic force microscopy. The hardness of joints near the interface was higher than that far away from the interface, which is attributed to the difference of structural relaxation. According to the result of micro-focused X-ray diffractometry and transmission electron microscopy, the joints retained the amorphous structure when the holding time is less than 20 min. The surface area fraction of oxide film on the interface of joints was detected by ultrasonic inspection. Moreover, the surface area fraction of oxide film is in excellent agreement with the theoretical value calculated by shear strength. The result indicated that surface oxide film is the dominant barrier on the diffusion bonding of bulk metallic glass rather than low atomic diffusion coefficient.     

基于FPGA的高速数据采集分析系统的设计

为了实现对模拟量的高速采集与快速傅里叶分析,提出了一种基于FPGA的高速数据采集分析系统的设计方案,系统采用Cyclone系列FPGA配合高速A/D转换器,并使用了Altera公司的定制快速傅里叶分析集成核,通信与上位机采用RS 232串行通信标准协议配合基于Matlab GUI的上位机分析软件,并对多组高频模拟信号进行了高速数据采集与快速傅里叶分析实验,同时在上位机分析软件中实时显示出分析结果。实验结果验证了快速傅里叶分析理论,实现了低成本、高性能数据采集分析系统的设计完成。     

Nonlinear optical properties and performance optimization of the pro-aromatic chromophores for NLO materials

Geometric structures and nonlinear optical properties (NLO) of the pro-aromatic chromophores, comprising indoline moiety as an electron donor and azo linker as a π-conjugated bridge, have been investigated by means of quantum chemistry method and the response theory. Three solvent models were used to study the short-range interaction and long-range interaction between solvent and solution in order to simulate the experimental spectra. Simulated absorption used by the polarizable continuum model gave a well agreement with experimental measurement. The micro-mechanisms of first hyperpolarizability were explained on the basis of the two-level models, and charge difference density methods demonstrated that the chromophore (4f), which indoline moiety acts as an electron donor and N,N-dimethyl formamide as an acceptor bridged by azo bridge, displays an efficient intramolecular charge transfer properties amplifying the NLO response. Calculations of two-photon absorption (TPA) for the indoline chromophore were performed to develop their potential application on TPA materials. Additionally, some molecules were designed by replacing electron donor and introducing additional heteroatoms to tune the NLO parameters. The results show 4f-a with 1,4-phenylenediamine donor unit and introducing one heteroatom display well NLO character.     

Polymer-supported N-heterocyclic carbene-iron(III) catalyst and its application to dehydration of fructose into 5-hydroxymethyl-2-furfural

Polymer-supported NHC–metal catalysts were prepared from chloromethyl polystyrene resin via two-step reaction. Metals were loaded into 1.6 – 16 mol% of total imidazolium and the remaining imidazolium chloride salt provided ionic liquid moiety. The formation of metal complex with the polymer-supported NHC ligand was analyzed by ATR FT-IR, XRD, and XPS. The synthesized polymer-supported NHC–metal catalysts were applied to the dehydration of fructose into HMF. The environmentally benign and inexpensive polymer-supported NHC–Fe^III catalyst showed good catalytic activity and yielded HMF at 73% (with a conversion of 97%). It could also be reused without significant loss of catalytic activity.     

Multiprocessor modeling of parallel Particle Swarm Optimization applied to nuclear engineering problems

Particle Swarm Optimization (PSO) is a population-based metaheuristic (PBM), in which solution candidates evolve through simulation of a simplified social adaptation model. Putting together robustness, efficiency and simplicity, PSO has gained great popularity. Many successful applications of PSO are reported, in which PSO demonstrated to have advantages over other well-established PBM. However, computational costs are still a great constraint for PSO, as well as for all other PBMs, especially in optimization problems with time consuming objective functions. To overcome such difficulty, parallel computation has been used. The default advantage of parallel PSO (PPSO) is the reduction of computational time. Master-slave approaches, exploring this characteristic are the most investigated. However, much more should be expected. It is known that PSO may be improved by more elaborated neighborhood topologies. Hence, in this work, we develop several different PPSO algorithms exploring the advantages of enhanced neighborhood topologies implemented by communication strategies in multiprocessor architectures. The proposed PPSOs have been applied to two complex and time consuming nuclear engineering problems: i) reactor core design (CD) and ii) fuel reload (FR) optimization. After exhaustive experiments, it has been concluded that: i) PPSO still improves solutions after many thousands of iterations, making prohibitive the efficient use of serial (non-parallel) PSO in such kind of real-world problems and ii) PPSO with more elaborated communication strategies demonstrated to be more efficient and robust than the master-slave model. Advantages and peculiarities of each model are carefully discussed in this work.     

Going electric: Expert survey on the future of battery technologies for electric vehicles

The paper describes the results of a survey carried out with leading EU experts on the future costs of batteries for electric and plug-in hybrid vehicles and the uncertainty surrounding them. Battery costs are one of the main components in the overall costs of EVs and improvements could be brought about by increased investments in research, development and demonstration (RD&D). Experts' judgements are collected to shed light on the inherently uncertain relationship between RD&D efforts and the consequent technical progress in batteries. The analysis of the experts' data results in a number of important policy recommendations to guide future RD&D choices and target commitments both for the EU and its member states.     

Microstructure and mechanical properties of the Si3N4/42CrMo steel joints brazed with Ag–Cu–Ti + Mo composite filler

The Si₃N₄ ceramic was joined to 42CrMo steel using Ag–Cu–Ti + Mo composite filler. Effect of Mo particles content on the microstructure and mechanical properties of the joints were investigated. Defect-free joints were received when the Si₃N₄/42CrMo steel joints were brazed with Ag–Cu–Ti + Mo composite filler. The results show that a continuous reaction layer which is composed of TiN and Ti₅Si₃ was formed near the Si₃N₄ ceramic. A double reaction layer which consists of Fe₂Ti and FeTi was also formed adjacent to 42CrMo steel, with Fe₂Ti being located near the steel. The central part of the joint is composed of Ag based solid solution, Cu based solid solution, Mo particles and some Cu–Ti intermetallic compounds. The maximal bending strength reached 587.3 MPa with 10 vol.% Mo particles in the joint, at which the joint strength was 414.3% higher than the average strength for the case without Mo particles addition.     

Formation of ZrC ablation protective coatings on carbon material by tungsten inert gas cladding technique

Continuous, uniform, crack-free ZrC protective coatings have been deposited by a novel tungsten inert gas cladding technique on graphitic carbon substrates through the reaction of graphitic carbon with ZrO₂. The phase composition, microstructure, and ablation performance have been researched. Cross-section morphology revealed that an excellent bond was formed at the coating/substrate interface. Ablation loss tests showed samples coated by tungsten inert gas cladding technique substantially increased the ablation resistance. Compared with uncoated samples, the mass loss rate decreased by 68.5% for the coated sample with a ZrO₂:C mole ratio of 1:1.2.     

Measurement of zeta potential of macroscopic surfaces with Navier velocity slip exploiting electrokinetic flows in a microchannel

A method devised to measure the zeta potential of macroscopic surfaces with Navier velocity slip non-destructively exploiting electrokinetic flows in a microchannel. For an accurate as well as facile determination of zeta potential using this method, we need a simple relationship between zeta potential and streaming potential for electrokinetic flows in microchannels with consideration of the possibility of the Navier velocity slip. In the present investigation, we derive a semi-analytic formula for this relationship based on a one-dimensional modeling of electrokinetic flow in microchannels, which is as accurate as the numerical solution of the full governing partial differential equations. This formula is expected to allow accurate measurements of zeta potential of various macroscopic surfaces with Navier velocity slip.