有底柱阶段自然崩落法系统的设计与实现

为了使设计人员快速而准确地得到最合理的给定矿体的有底柱阶段自然崩落采矿法的二维图形和三维可视化模型的模拟图,文中通过分析有底柱自然崩落采矿法的生产过程（采准、切割、回采）以及读入的预先生成的矿体信息并将提取分析出来的崩落采矿法信息作为参数,实现了有底柱自然崩落采矿法系统的设计与实现。设计人员在使用该系统时,只需将分析得到的崩落采矿法信息输入,并读入预先生成的矿体即可得到基于该矿体的有底柱阶段自然崩落法的二维图形和三维模型的模拟图。使用该系统使得设计人员能够快速地得到该采矿方法的二维和三维模型的模拟图,给设计人员带来了方便,在采矿领域起着极其重要的作用。     

Fatigue strength and microstructure evaluation of Al 7050 alloy wires recycled by spray forming,extrusion and rotary swaging

Recycled high-strength aluminum alloys have limited use as structural materials due to poor mechanical properties. Spray forming remelting followed by hot extrusion is a promising route for reprocessing 7xxx alloys. The 7050 alloy machining chips were spray formed, hot extruded, rotary swaged and heat-treated in order to improve mechanical properties. Microstructures, tensile properties and fatigue strength results for a 2.7 mm-diameter recycled wire are presented. Secondary phases and precipitates were investigated by XRD, SEM, EBSD, TEM and DSC. As-swaged and heat-treated (solution and aging) conditions were evaluated. Mechanical properties of both conditions outperformed AA7050 aerospace specification. Substantial grain refinement resulted from the extensive plastic deformation imposed by rotary swaging. Refined micrometric and sub-micrometric Al grains, as well as coarse and fine intermetallic precipitates were observed. Subsequent solution treatment resulted in a homogeneous, recrystallized and equiaxed microstructure with grain size of 9 μm. Nanoscale GP(I) zones and η′ phase precipitates formed after aging at 120 °C, imparting higher tensile (586 MPa) and fatigue (198 MPa) strengths.     

The false promises of coal exploitation: How mining affects herdsmen well-being in the grassland ecosystems of Inner Mongolia

The grasslands of Inner Mongolia are not only the source of the necessary resources for the survival and development of herdsmen, but also represent a significant green ecological barrier in North China. Coal-mining production is important in maintaining GDP growth in Inner Mongolia. However, over-exploitation has created serious problems, such as pollution of the environment and significant decreases in grassland ecosystem services, in addition to impacting the well-being of herdsmen and other humans. Based on questionnaires survey performed among 864 herdsmen addressing the relationship between coal exploitation in grasslands and human well-being in Xilinguole League in Inner Mongolia, we found that (1) coal resource exploitation in these grasslands does not benefit the herdsmen by increasing their income; (2) the rapid development of this resource has not obviously materially improved the life of the herdsmen; and (3) these activities have increased the risks that herdsman will have to endure in the future. Overall, coal resource exploitation in grasslands has more negative than positive effects on the well-being of herdsmen. We propose the conservation of coal resources and improvement of ecological compensation should be carried out without blindly pursuing economic growth, instead of focusing on economic development and structural adjustments.     

基于AT89S51的密码锁设计

针对传统机械锁结构简单、安全性能低的特点,采用AT89S51单片机作为主控芯片,结合外围的按键电路、显示电路、报警电路、存储电路以及开锁电路,设计出一款可以多次更改密码,并且具有声音报警功能的电子密码锁。实践证明,该密码锁具有设计方法合理,简单易行,成本低,使用安全等特点。     

Prediction of anode performances of direct methanol fuel cells with different flow-field design using computational simulation

Three-dimensional computational simulation was employed to illustrate the performance characteristics according to the flow-field design by solving the physics in the flow field and the diffusion layer and by calculating the electrochemical reaction at the catalyst layer. The pressure loss and the concentration distribution in the anode were analyzed for four types of flow field, parallel, serpentine, parallel serpentine and zigzag type. Also the anode current density distribution was predicted at the various overpotentials. The cell performance was proportional to the pressure drop for all the flow-field types. Zigzag type showed the best performance which has a good resistance against the fuel concentration polarization and the next was serpentine.     

Ion release from three lead-free piezoelectric ceramics and their physical and cytotoxicity characteristics

The ions released from the polarized potassium sodium niobate (KNN), lithium-doped potassium sodium niobate (LKNN) and barium titanate (BT) specimens after soaking in a normal saline up to 28 days were monitored. The cytotoxicity of ion released products was evaluated. The cytotoxicity testing on these three lead-free piezoelectric ceramics exhibited low toxicity. However, the decrease of biaxial strength for KNN and the decrease of piezoelectric charge coefficient d₃₃ for LKNN were noted after soaking in saline solution. Such decreases can be related to the release of ions from the surface of the KNN and LKNN specimens during soaking in saline solution.     

压电换能器在串并联谐振频率附近的特性研究

研究了压电换能器在串、并联谐振频率附近工作时的特性.采用等效电路变换的方法,推导出了换能器在串联、并联谐振频率附近时,串联、并联匹配电感参数以及有功电阻的表达式.结果表明电感匹配可以提高有效机电耦合系数.     

Prediction of hot tearing susceptibility of direct chill casting of AA6111 alloys via finite element simulations

To predict hot tearing susceptibility (HTS) during solidification and improve the quality of Al alloy castings, constitutive equations for AA6111 alloys were developed using a direct finite element (FE) method. A hot tearing model was established for direct chill (DC) casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion. By applying this model to real manufacture processes, the effects of casting speed, bottom cooling, secondary cooling, and geometric variations on the HTS were revealed. The results show that the HTS of the billet increases as the speed and billet radius increase, while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases. This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation, which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.     

Microstructure and mechanical properties of 7075 aluminum alloy during complex thixoextrusion

7075 aluminum alloy was used to obtain elbow parts by complex thixoextrusion and the microstructure evolution and mechanical properties during this process were studied by SEM, TEM and other analytical methods. The results show that different parts in 7075 aluminum alloy show quite different microstructures. The microstructure of the thin walls formed by back-extrusion is stratified, and the bottom of the parts formed by angular extrusion is obviously deformed. Shear forces contribute to the crushing of grains and the coarse second phase. The main strengthening phases in the material are η phase and E phase, whose amounts greatly decrease during heating to semi-solid and thixoextrusion. After heat treatment, they can precipitate evenly to improve the mechanical properties of the material. The average tensile strength of whole part after thixoextrusion and heat treatment is 485.49 MPa, while the average elongation is 5.49%.     

Numerical analysis on combustion process and sodium transformation behavior in a 660 MW supercritical face-fired boiler purely burning high sodium content Zhundong coal

CHEMKIN software was used to optimize the reaction mechanism of sodium in flue gas to study the influence of targeted design for purely burning Zhundong (ZD) coal on boiler characteristics. Then, the optimized 32-step elemental reaction was combined with CFD software. An eddy-dissipation concept model considering detailed chemical reactions was used to simulate the transformation behavior of sodium-containing substances. The combustion characteristics of the 660 MW face-fired boiler under various loads were also simulated. The field distribution in the furnace and the migration path of sodium along the track of pulverized coal particles were obtained. The results show that the interference between each burner in the furnace is small at the BMCR load, and the phenomenon of “wind wrapping fire” is distinctly clear. The temperature at furnace outlet is approximately 970.98 °C. At a low load, the combustion in the furnace is stable, and the temperature at the furnace outlet reaches the design value. The sodium present in ZD coal is involved in the reaction after it is released in the form of Na and NaCl. Sodium is present in different forms in the main burner zone, mainly NaCl (67%), NaOH (12%), Na (9%), and Na₂SO₄ (7%). The forms of sodium at the furnace outlet are NaCl (50%), Na₂SO₄ (37%), Na₂Cl₂ (9%) and NaHSO₄ (4%). A small amount of Na₂SO₄ is formed by NaHSO₄ reaction in the main burner zone. It then reacts to form NaSO₄, wherein NaHSO₄ is formed by path 2. Na₂SO₄ is mainly generated in the burnout zone through path 1, and paths 2, 3, and 4 are hardly observed. The findings of this research can provide reference for the design of a purely fired ZD coal boiler and further studies on slagging observed on the heating surface.