A kinetic model involving oxidation and volatilization in SiC-B4C-xAl2O3 ceramics system

In this paper, a new kinetic model considering both oxidation and volatilization kinetics is established and applied to analyze the oxidation of SiC-B₄C-xAl₂O₃ ceramics and other systems in various oxidation conditions. The effects of diffusion area and volume changes during the oxidation process are considered in this model. The physical meaning of each parameter in this model is explicit and simple. According to this model, the diffusion coefficient of species and the corresponding diffusion activation energy are easily available. The practicability of this model is well verified by the experimental data of SiC-B₄C-xAl₂O₃ and other systems oxidized under different conditions. In addition, the practice shows that the model is applicable not only to the systems where oxidation and volatilization coexist, but also to the system where only oxidation plays a major role. We hope the model proposed in this work can be used in other materials with more complex environments.     

改进的DNA免疫遗传算法在车间调度中的应用

根据生命科学中免疫系统的信息处理机制,在一般遗传算法的基础上,将免疫算法和DNA遗传算法相结合,提出一种用于车间调度的新DNA免疫遗传算法。引入一个遗传密码表,用于DNA碱基链的解码;算法中子群体之间的信息交换采用孤岛模型;引入一个疫苗库,通过接种疫苗提高抗体的适应度,通过免疫选择防止种群的退化。这些改进措施对降低算法的复杂程度、提高算法的收敛速度和全局搜索能力有重要意义。应用标准测试集中的测试用例和实际调度中的问题对改进后的算法进行了测试。仿真程序表明,该算法能以较快的速度完成给定范围的搜索和全局优化任务。     

金属脊和H形调谐枝节对微带天线的频带影响分析

设计了一种新型Ku波段宽频带微带天线.提出了在介质基板间加入金属脊和在贴片上加H形调谐枝节的新方法.仿真结果表明,增加金属脊可将相对带宽展宽至21.4%,金属脊形状对带宽无明显影响.同时增加金属脊和H形调谐枝节,可将带宽进一步展宽至23.6%.     

A Comparative study of organic fouling in hollow fiber and spiral wound membranes

The occurrence of flux decline in brackish water reverse osmosis (RO) plants due to dissolved organics is a topic of ongoing research. This type of organic fouling has also been found in seawater RO plants. A study was undertaken to compare organic fouling in hollow fiber and spiral wound membranes using a seawater feed that possessed a high concentration of huraic acid. This study was undertaken at an RO plant on Grand Cayman Island, British West Indies. The feed water came from a sea well and possessed a concentration of humic acid that varied between 35 and 60 mg/l.The hollow fiber membrane was operated at a recovery of 25% while the recovery with the spiral wound membrane varied between 5 and 25%. The performance data which included permeate flow, salt rejection, pressure drops across the membrane and analysis of the membranes for organic fouling were undertaken. This study compared the performance data and organic fouling between the hollow fiber and spiral wound meembranes.     

Automated design of optimum pipeline in chemical industry

Quick in operation heuristic-decomposition methods of choosing the optimum way of equipment deployment units and pipelines in pipeline systems are suggested. They are based on utilisation of the bank of knowledge on the essence of hydrodynamic, technological, physico-chemical, geometrical and construction conditions of functioning of pipelines systems, apparatus and machnery in chemical industry and also heuristic-computation procedures of regular search for optimum solutions on generalised hypothetic construction graphs which are descreet models of geometrical space.     

Directly operated valve for space cryostats

Space cryostats like that of the Infrared Space Observatory (ISO) need a number of valves for cryogen management at different temperature levels. The ISO cryostat was defined as a hybrid cooling system using liquid hydrogen and superfluid helium during the ISO phase A study. A directly electrically operated bistable latch-valve was developed and prequalification tested for application within the H₂ subsystem and the He ll subsystem of the ISO cryostat. This valve is operable at all temperatures between 1.7 and 300 K and with H₂ and He in all phases (liquid, superfluid, gaseous) occurring within the cryostat. The valve offers very high leak tightness at higher temperatures and sufficient leak-tightness even with He ll. The heat dissipation for actuating the valve at liquid helium temperatures is only 0.03 W s, a value which is, to our knowledge, not reached by any other valve of comparable size and application. The valve operating electrical pulse is shorter than 0.1 s and the valve is held in a closed as well as open position by permanent magnets without using electrical energy.     

Real time eco-driving of high speed trains by simulation-based dynamic multi-objective optimization

Eco-driving is a traffic operation measure that may lead to important energy savings in high speed railway systems. Eco-driving optimization has been applied offline in the design of commercial services. However, the benefits of the efficient driving can also be applied on-line in the regulation stage to recover train delays or in general, to adapt the driving to the changing conditions in the line. In this paper the train regulation problem is stated as a dynamic multi-objective optimization model to take advantage in real time of accurate results provided by detailed train simulation. If the simulation model is realistic, the railway operator will be confident on the fulfillment of punctuality requirements. The aim of the optimization model is to find the Pareto front of the possible speed profiles and update it during the train travel. It continuously calculates a set of optimal speed profiles and, when necessary, one of them is used to substitute the nominal driving. The new speed profile is energy efficient under the changing conditions of the problem. The dynamic multi-objective optimization algorithms DNSGA-II and DMOPSO combined with a detailed simulation model are applied to solve this problem. The performance of the dynamic algorithms has been analyzed in a case study using real data from a Spanish high speed line. The results show that dynamic algorithms are faster tracking the Pareto front changes than their static versions. In addition, the chosen algorithms have been compared with the typical delay recovery strategy of drivers showing that DMOPSO provides 7.8% of energy savings.     

Synthesis and plasma treatment of nitrogen-doped graphene fibers for high-performance supercapacitors

Graphene fiber-based supercapacitor has aroused great interest as a flexible power source in future wearable electronics. However, the low electrochemical performance of graphene fibers (GFs) usually causes the serious limitation of use in practical applications due to the material stacking, hydrophobicity and fabrication process complexity. In this work, a facile and effective plasma-assisted strategy is put forward to increase specific surface area, tune hierarchically porous structure and promote wettability of nitrogen-doped graphene fibers (NGFs), resulting in the improvement of electrochemical performance. The supercapacitor assembled from plasma-treated NGFs shows superior capacitance (878 mF/cm² at 0.1 mA/cm² current density) and high energy density (19.5 μW h/cm² at 40 mW/cm² power density), which is 23.7% and 131.4% higher than that of NGFs and GFs, respectively. Additionally, the fiber-based supercapacitor based on plasma-treated NGFs exhibits high rate capability of 59.8% and excellent cyclic performance (95.8% retention over 10,000 cycles). These plasma-treated NGFs can be promising candidates for high-performance and flexible power sources in future wearable electronics.     

Piezoelectric and mechanical properties of CaO reinforced porous PZT ceramics with one-dimensional pore channels

The formation of capillaries in sodium alginate gels is a dissipative process driven by unidirectional diffusion of divalent cations into sodium alginate sols. In the present work, we have prepared 3-1 type porous lead zirconate titanate (PZT) ceramics with oxides (CaO) being doped on a molecular level from the dissipative process by incorporating PZT particles into the sodium alginate gel matrix. By varying the concentration of cation solutions (CaCl₂) from 0.5 mol/L to 2.5 mol/L, both the microstructure, doping amount of oxides (CaO) and crystalline phase of the porous PZT ceramics were tailored. Accordingly, increase in the concentration of Ca²⁺ has led to a reduction in the relative permittivity (ε_r) first, and then an increase, while the piezoelectric coefficient (d₃₃ and d₃₁) demonstrated an opposite variation tendency. The prepared samples possessed a maximal HFOM value of 4755×10^–15 Pa⁻¹ when the concentration of Ca²⁺ was 1.0 mol/L. Addition of CaO was found to improve the compressive strength of porous PZT ceramics, which was preferential to promoting the stability and reliability for application.