Ag–Cu–BTC prepared by postsynthetic exchange as effective catalyst for selective oxidation of toluene to benzaldehyde

A mixed-node MOF catalyst Ag–Cu–BTC was prepared by postsynthetic exchange (PSE) method. It is believed that PSE method can realize isomorphous replacement of Ag ion to framework Cu ion in Cu–BTC successfully. The catalytic performance of Ag–Cu–BTC was investigated via selective oxidation of toluene to benzaldehyde by molecular oxygen in the absence of solvent and initiator. This catalyst exhibits good catalytic performance: on the premise of keeping highly selective catalysis of Cu–BTC for toluene oxidizing to benzaldehyde, the introduction of Ag (Ag content is 2.76 wt.%) can promote toluene conversion from 6.5% to 12.7%.     

Effect of grinding-induced cyclic heating on the hardened layer generation in the plunge grinding of a cylindrical component

This paper discusses the effects of the grinding-induced cyclic heating on the properties of the hardened layer in a plunge cylindrical grinding process on the high strength steel EN26. It was found that a multi-pass grinding brings about a uniform and continuous hardened layer along the circumference of the cylindrical workpiece. An increase of the number of grinding passes, leads to a thicker layer of hardening, a larger compressive residual stress and a deeper plastic deformation zone. Within the plastic deformation zone, the martensitic grains are refined by the thermo-mechanical loading, giving rise to a hardness of 12.5% higher than that from a conventional martensitic transformation. The coupled effects of heat accumulation and wheel wear in the multi-pass grinding are the main causes for the thickening of the hardened layer. A too small infeed per workpiece revolution would result in insufficient grinding heat, and in turn, bring about an undesirable tempered hardened layer and a reduction of its hardness.     

Influence of the ZrB2 content on the anti-oxidation ability of ZrB2-SiC coatings in aerobic environments with broad temperature range

ZrB₂-SiC coatings with different ZrB₂ contents were prepared by liquid phase sintering. The oxidation processes of coatings were explained according to TG results of ZrB₂-SiC coatings and powders tested from 298 K to 1773 K. Results show that, increasing ZrB₂ content made the weight of the samples changed from weight-loss of 10.04% to weight-gain of 0.14%, while the fastest weight-loss regions were narrowed, whose inflection points reduced from 1310℃ to 1050℃. Increasing ZrB₂ content made the relative oxygen permeability of the ZrB₂-SiC/SiC coatings reduced from 40%–60% to -10%-5%. Increasing ZrB₂ content enhanced high-temperature stability of coatings, making final weight of samples changed from weight-loss of 0.16% to weight-gain of 0.11% after oxidation at 1773 K for 200 h. The peeling and dispersion of Zr-oxides formed Zr-B-Si-O compound glass layer, presenting enhanced stability, dispersion strengthening and pinning effect of Zr-oxides, which were responsible for the excellent anti-oxidation protective effect of coatings in a broad temperature region.     

Multi-objective layout optimization for an orbital propellant depot

Structural and Multidisciplinary Optimization - The overall layout optimization design of an orbital propellant depot involves the optimization of shape, size, and positions of propellant tanks in...     

Flame Front Deformation Instabilities of Filtration Combustion for Initial Thermal Perturbation

The flame front deformation instability of low-velocity filtration combustion within an inert packed bed is studied based on the initial preheating non-uniformity. Based on the experimental phenomena, an initial thermal perturbation model is numerically proposed so as to predict the deformation behaviors of the flame front instabilities. The numerical prediction indicates that the assumption of an initial thermal perturbation is a feasible explanation as the cause of the flame front inclination instability. As the initial thermal perturbation increases, the phenomena of the flame front break and shrinking instabilities could easily occur at high filtration velocity or low equivalence ratio. Moreover, the evolutions of the flame front break rate and the shrinking rate are quantitatively analyzed.     

Investigation of performance variations due to the amplitude of group-delay ripple in chirped fiber Bragg gratings

We measure the system impacts due to the amplitude of group-delay (GD) ripple in single and cascaded chirped fiber Bragg gratings (CFBGs). Signals with smaller pulse width result in smaller performance variation at the same data rate. A 65-ps peak-to-peak GD ripple induces 0.9, 1.7, and 2.7 dB maximum penalties for 10, 20, and 40-Gb/s, respectively. We also find that cascading gratings with random ripple causes much less degradation than cascading gratings with the same ripple profile.     

OFDM系统中同步算法的FPGA 实现

给出了一种用于 OFDM 系统中可同时完成帧起始位置估计和载波频偏估计／补偿的同步算法及其 FPGA 实现方法。采用量化的方法对该不需要额外同步序列的估计算法进行了改进,提高了载波频偏的估计精度,并在数字域进行了频偏校正。在硬件实现上,利用 CORDIC 算法能够有效计算三角函数的特点,把频偏估计和频偏校正过程中的反正切运算和角度旋转操作转化成加法和移位操作,实现了计算精度、运算速度和硬件资源利用三方面性能的兼顾。     

Fatigue crack growth in SiC particulates reinforced Al matrix graded composite

The SiC/Al graded composite was fabricated by powder metallurgy processing and its fatigue crack growth behavior was studied. The volume percentage of SiC particulates was distributed from 5 to 30% layer by layer on the cross section. Since the aluminium was dissolved together, there was no evident interface between the two layers with different volume fraction of SiC particulates. Fatigue crack growth was in direction of from 5 to 30% SiC layers under sinusoidal wave-form. The retardation of fatigue crack growth was found when crack propagated from low volume fraction of SiC to high volume fraction of SiC. The crack deflection and branching between two layers were observed, which decreased crack growth rates. In view of crack tip driving force, the plasticity mismatch between the layers shielded crack tip driving force, i.e. decreased the effective J-integral at the tip of the crack as the plastic zone of the crack tip spread from the weaker material into the stronger material.     

单微乳液中制备Ag/TS-1及丙烯气相环氧化

采用N2H4还原含AgNO3的单微乳液制备了Ag／TS-1催化剂。TEM表征结果表明，Ag高度分散于TS-1之上。以H2、O2存在下的丙烯气相环氧化为探针反应，考察了Ag／TS-1的催化性能。结果表明，采用Ag／TS-1为催化剂，Ag的负载量为1％（质量分数，下同），823 K焙烧后，373 K下反应30 min时，丙烯转化率为1．69％，环氧丙烷（Propylene oxide，PO）选择性为93．2％。当Ag的负载量超过2％时，反应过程中生成大量的热，造成PO的选择性下降。采用Ag的负载量为8％的Ag／TS-1催化剂，消除热效应后，丙烯的转化率为2．46％．PO的选择性为79．2％。     

The Effect of the Charge Fluctuation of Dust Parti-cles on Ion-acoustic Wave Excited Through Ionization Instability

The effect of the charge fluctuation of dust particles on ion acoustic wave (IAW) excited through ionization instability was investigated. The hydrodynamic equations and linear time-dependent perturbation theory served as the starting point of theory, by which the dispersion relation and growth rate of the IAW were given. By comparing the results with the case of constant dust charges, it was found that the charge fluctuation of dust particles reduces the instability of the wave mode.