High-entropy titanate pyrochlore as newly low-thermal conductivity ceramics

Low-thermal conductivity ceramics play an indispensable role in maximizing the efficiency and durability of hot end components. Pyrochlore, particularly zirconate pyrochlore, is currently a highly promising and widely studied candidate for its extremely low thermal conductivity. However, there are still few pyrochlores that offer both stiffness, insulation, and good thermal expansion properties. In this work, the solidification method was innovatively introduced into the preparation of titanate pyrochlore, and combined it with the compositional design of high-entropy. Through careful composition design and solidification control, the high-density and uniform elements distributed high-entropy titanate pyrochlore ceramics were successfully prepared. These samples possess high hardness (15.88 GPa) and Young’s modulus (295.5 GPa), low thermal conductivity (0.947 W·m^?1·K^?1), excellent thermal expansion coefficient (11.6 ×10^?6/K) and an exquisite balance between stiffness and insulation (E/κ, 312.1 GPa·W^?1·m·K), in which the E/κ exhibits the highest value among the current reported works.     

Efficiency evaluation of healthcare services in China based on stochastic multicriteria acceptability analysis and directional distance function

Evaluating the efficiency of healthcare services accurately can help in analyzing the rationality of inputs and outputs in such services. Considering the consistency and equity of assessment criteria, this study conducts the stochastic multicriteria acceptability analysis (SMAA-2) with a directional distance function to evaluate the efficiency of healthcare services in 31 provincial administrative regions of mainland China, as observed in 2018. We use SMAA-DDF to explore all the projection directions to the efficient frontier instead of a certain projection direction. We measure the maximum and average efficiencies for each of the 31 provincial healthcare services. Our empirical findings show that only seven provinces achieve optimal healthcare service efficiency; the eastern area performed the best, followed by the central, western, and northeast areas. Furthermore, the path along the projection directions is provided to help inefficient provinces improve their efficiency and obtain the best possible positions.     

Microstructural and mechanical properties assessment of transient liquid phase bonding of CoCuFeMnNi high entropy alloy

The transient liquid phase (TLP) bonding of CoCuFeMnNi high entropy alloy (HEA) was studied. The TLP bonding was performed using AWS BNi-2 interlayer at 1050 °C with the TLP bonding time of 20, 60, 180 and 240 min. The effect of bonding time on the joint microstructure was characterized by SEM and EDS. Microstructural results confirmed that complete isothermal solidification occurred approximately at 240 min of bonding time. For samples bonded at 20, 60 and 180 min, athermal solidification zone was formed in the bonding area which included Cr-rich boride and Mn₃Si intermetallic compound. For all samples, the γ solid solution was formed in the isothermal solidification zone of the bonding zone. To evaluate the effect of TLP bonding time on mechanical properties of joints, the shear strength and micro-hardness of joints were measured. The results indicated a decrement of micro-hardness in the bonding zone and an increment of micro-hardness in the adjacent zone of joints. The minimum and maximum values of shear strength were 100 and 180 MPa for joints with the bonding time of 20 and 240 min, respectively.     

煤层顶板硬岩大直径定向钻孔施工关键技术

根据顶板高位定向钻孔快速钻进成孔与工作面卸压瓦斯高效抽采治理需要，针对现有螺杆马达定向钻进技术与分级扩孔方法存在的问题，开展了顶板硬岩定向钻进与大直径扩孔钻进关键技术研究，开发了冲击回转定向钻进技术、扭冲回转定向钻进技术、扭冲旋转扩孔技术以及双级双速扩孔技术等钻孔提速新技术，研制了冲击螺杆马达、矿用小直径扭力冲击器、双级双速螺杆马达、组合式扩孔钻头等配套钻具。综合试验结果表明，硬岩定向钻孔平均机械钻进效率达到8.34 m/h，最高达到13.6 m/h，较常规螺杆马达定向钻进技术提升20%~30%；硬岩大直径扩孔终孔直径达到200 mm，机械钻进效率平均达到5.6 m/h以上，最高达到10.5 m/h。该技术提升了顶板硬岩定向钻进效率与大直径扩孔钻进效率，缩短了顶板高位定向钻孔的综合施工周期，为大直径高位定向长钻孔快速成孔与高效抽采治理回采工作面卸压瓦斯提供了可靠的技术手段。     

喷射成形Al-Zn-Mg-Cu合金挤压态的组织和力学性能

研究了利用喷射成形辅以挤压制备Al-5.72Zn-2.36Mg-1.66Cu合金后优化的组织结构特征和力学性能。结果表明,合金基体组织均匀细化,晶粒形貌趋于圆整,平均晶粒大小达到10 μm左右。当合金的冷却条件通过快速凝固技术改变时,会产生不同程度的固溶强化效果和第二相弥散强化效果,从而改善了合金的整体性能。合金的屈服强度和抗拉强度分别平均提高了20%左右,且伸长率也略有提高。     

Formation of twinned dendrites during unidirectional solidification of Al-32%Zn alloy

The present study focused on the formation and crystallographic orientation of twinned dendrites coexisting with equiaxed grains in unidirectional solidification of Al-32%Zn (mass fraction) alloy. The morphology was investigated by optical metallograph and electron back-scattered diffraction technique. Results showed that the macrostructure of the alloy exhibited a typical feathery and fan-like structure while the microstructures were elongated lamellas, which were separated by coherent and incoherent twin boundaries. Both the primary trunk and all lateral arms of twinned dendrites grew along 〈110〉 directions, unlike regular 〈100〉 α(Al) dendrites. The facet growth of crystals at solid/liquid interface was responsible for the origin of twinned dendrites during the weak local convection, and high thermal gradient and medium solidification velocity had significant contribution to the formation of twinned dendrites. The formation mechanism of twinned dendrites which consisted of three multiplication ways of new twin boundaries formation and one way of dendrite evolution in twin plane was shown schematically.     

Cellular/dendritic transition,dendritic growth and microhardness in directionally solidified monophasic Sn-2%Sb alloy

Horizontal directional solidification experiments were carried out with a monophasic Sn-2%Sb (mass fraction) alloy to analyze the influence of solidification thermal parameters on the morphology and length scale of the microstructure. Continuous temperature measurements were made during solidification at different positions along the length of the casting and these temperature data were used to determine solidification thermal parameters, including the growth rate (V_L) and the cooling rate (T_R). High cooling rate cells and dendrites are shown to characterize the microstructure in different regions of the casting, with a reverse dendrite-to-cell transition occurring for T_R>5.0 K/s. Cellular (l_c) and primary dendrite arm spacings (l₁) are determined along the length of the directionally-solidified casting. Experimental growth laws relating l_c and l₁ to V_L and T_R are proposed, and a comparative analysis with results from a vertical upward directional solidification experiment is carried out. The influence of morphology and length scale of the microstructure on microhardness is also analyzed.     

Deploy Efficiency Driven k-Barrier Construction Scheme Based on Target Circle in Directional Sensor Network

Journal of Computer Science and Technology - With the increasing demand for security, building strong barrier coverage in directional sensor networks is important for effectively detecting...     

煤层顶板裂隙高位定向长钻孔安全高效抽采技术的研究与应用

放顶煤开采期间，上覆岩层受到矿压的影响，形成冒落带、裂隙带、弯曲下沉带，工作面采空区遗煤和围岩涌出的大量瓦斯飘浮在上方裂隙带区域，造成瓦斯聚集并向外涌出，形成了安全隐患，因此必须将该区域瓦斯抽出来；以往治理采空区瓦斯主要采用顶板裂隙高位钻场、顶板高抽巷等措施，但是这2种方法施工成本较高，且施工周期长，对生产接替影响较大。煤层顶板裂隙高位定向长钻孔安全高效抽采采用大功率钻机+定向钻进技术，在裂隙带施工控制整个回采范围的长钻孔，减少采空区和邻近层瓦斯向工作面空间的流动，真正实现了“以孔代巷”，既节省了成本，又缩短了工期，还提高了采空区瓦斯抽采的连续性、稳定性，减少了采空区瓦斯向外涌出，提升了瓦斯抽采效果，促进了煤矿安全高效发展。