Effect of Nb content on the phase composition,densification, microstructure,and mechanical properties of high-entropy boride ceramics

Dense high-entropy (Hf,Zr,Ti,Ta,Nb)B₂ ceramics with Nb contents ranging from 0 to 20 at% were produced by a two-step spark plasma sintering process. X-ray diffraction indicated that a single-phase with hexagonal structure was detected in the composition without Nb. In contrast, two phases with the same hexagonal structure, but slightly different lattice parameters were present in compositions containing Nb. The addition of Nb resulted in the presence of a Nb-rich second phase and the amount of the second phase increased as the Nb content increased. The relative densities were all >99.5 %, but decreased from ～100 % to ～99.5 % as the Nb content increased from 0 to 20 at%. The average grain size decreased from 13.9 ± 5.5 μm for the composition without Nb additions to 5.2 ± 2.0 μm for the composition containing 20 at% Nb. The reduction of grain size with increasing Nb content was due to the suppression of grain growth by the Nb-rich second phase. The addition of Nb increased Young’s modulus and Vickers hardness, but decreased shear modulus. While some Nb dissolved into the main phase, a Nb-rich second phase was formed in all Nb-containing compositions.     

Water Pipeline Leak Measurement Using Wavelet Packet-based Adaptive ICA

Water Resources Management - The localization of the leaks is estimated using the time difference method in the past decade. Generalized and Basic Cross-correlation techniques are frequently...     

Design of an Electromagnetic Frequency Tunned Antenna for Mobile Communications

Wireless Personal Communications - Current mobile communications technology relies heavily on efficient design of antennas, where the operational characteristics of the wireless communication...     

水泥对红壤pH值及植物生长影响的试验研究

中国南方地区广泛分布的酸性红壤严重影响植物的正常生长.针对此问题,以水泥掺量为0.1％、1％、2％、3％、4％的红壤为研究对象,开展了水泥对红壤pH值影响试验和盆栽种植试验.水泥对红壤pH值影响试验结果表明:红壤pH值随着水泥掺量的增加而增加,并随养护时间增加,pH值不断减小.养护28 d后,水泥掺量每增加1％,红壤pH值增加0.75.盆栽种植试验研究表明:当水泥掺量为0.1％时,狗牙根发芽率和生长高度表现最好,随着水泥掺量的增加,狗牙根发芽率降低,生长高度不断减小.水泥掺量每增加1％,狗牙根发芽率减少12.63％,狗牙根生长高度排序为:0.1％＞1％＞2％＞3％＞4％.     

单自由度八杆仿生机构构型与尺度同步设计方法

单自由度八杆仿生机构杆长参数较多，是仿生机器人领域研究的难点之一。为提高设计效率，提出一种构型与尺度同步设计方法。在选定的运动链和机架的基础上，以不等式形式分步给出运动可行性及外形约束条件，使得上一步的杆长可作为下一步求解的已知值。通过该过程，在得到八杆仿生机构构型的同时，快速得到所有杆长的初步可行域。循环上述过程，逐步缩小约束条件的范围，可使得八杆机构的杆长快速接近目标值。在此基础上，分类讨论了连杆搭接顺序、约束条件及基本运动链的差异对求解难度及构型结果的影响。利用所提出的单自由度八杆仿生机构的设计方法，在对初始条件进行合理选取的前提下，可在初步得到构型的同时将杆长限定在较小范围内，实现了构型与尺度的同步设计。该方法还可应用于其他单自由度机构的设计当中，具有较好的借鉴意义。     

Electrically Active States of Charge Capture and Transfer Causing Slow Recombination in Thallium-Bromide Crystals at Low Temperatures

TlBr single crystals grown by the Bridgman–Stockbarger method are studied. It is established that frozen-conductivity effects manifest themselves under interband excitation by light at temperatures below 200 K. Herewith, clearly pronounced superlinear dependences of the induced photoconductivity on the strength of the applied electric field manifest themselves. The results of studying thermally stimulated conductivity evidence that these phenomena can be associated with the filling of trap states with thermal activation energies of 0.08–0.12 eV. This state can be removed due to thermal quenching at temperatures of ?180 K because of the emptying of energy states with an activation energy of 0.63–0.65 eV filled after optical generation.     

瓦斯抽放钻孔涌水综合治理技术实践

针对高河矿W4307回风顺槽132-1#瓦斯抽放钻孔在施工过程中出水的问题,分析出水原因,在不起拔钻孔钻杆的情况下,对瓦斯抽放钻孔进行扩孔、安装套管、注浆固管及安装阀门控制放水,保证了孔口管的固结效果。试验表明:在放水过程中钻孔没有出现破坏,孔口管壁没有出现渗水和涌水现象,瓦斯抽放钻孔涌水治理效果良好。     

含新型有机硅缓蚀剂的制备及性能研究

为了研究缓蚀剂组分及添加条件对发射药性的影响,设计并制备了一种含新型有机硅的缓蚀剂材料;采用烧蚀管法,对比石蜡+TiO2型缓蚀剂,研究了新型有机硅缓蚀剂的静态降烧蚀效果;采用密闭爆发器研究了不同缓蚀剂添加条件对高能硝胺发射药点火和燃烧性能的影响;采用14.5mm弹道枪和壁温测试装置,研究不同缓蚀剂添加条件对膛壁温度、内弹道性能和枪口烟雾的影响。结果表明,采用含新型有机硅的缓蚀剂,降烧蚀效果更为显著;随着缓蚀剂添加量的增加,压力峰值、弹丸初速也会产生小幅下降,但总体影响幅度较小;添加缓蚀剂后,射击过程膛壁峰值温度显著下降,下降幅度随着缓蚀剂添加量的增加而增加,在缓蚀剂质量分数为3%时,对身管壁温降低幅度可达17.1%,且产生的枪口烟雾量较少;在缓蚀剂质量分数为5%时,缓蚀剂添加过量,枪口产生较大烟雾。该缓蚀剂及添加条件有望应用于低烧蚀发射药配方中。     

Personalized broad learning system for facial expression

Multimedia Tools and Applications - Understanding human emotions through facial expressions is key enabling technology for interactive robots. Most approaches of facial expression recognition are...     

Product design: Formulation of a screen-printable sintering-type conductive paste

Due to the complexity of the screen-printing operation and the rheological behaviors of the screen-printable paste, such a paste is usually formulated by trial-and-error. In this report, a systematic procedure, based on heuristics and mechanistic models, for the design of a screen-printable paste is developed. The procedure is demonstrated by a case study of the formulation of a conductive paste of copper particles.