Competitive effects of free volume,rigidity, and self-adaptivity on indentation response of silicoaluminoborate glasses

Lithium aluminoborate glasses have recently been found to feature high resistance to crack initiation during indentation, but suffer from relatively low hardness and chemical durability. To further understand the mechanical properties of this glass family and their correlation with the network structure, we here study the effect of adding SiO₂ to a 25Li₂O–20Al₂O₃–55B₂O₃ glass on the structure and mechanical properties. Addition of silica increases the average network rigidity, but meanwhile its open tetrahedral structure decreases the atomic packing density. Consequently, we only observe a minor increase in hardness and glass transition temperature, and a decrease in Poisson's ratio. The addition of SiO₂, and thus removal of Al₂O₃ and/or B₂O₃, also makes the network less structurally adaptive to applied stress, since Al and B easily increase their coordination number under pressure, while this is not the case for Si under modest pressures. As such, although the silica-containing networks have more free volume, they cannot densify more during indentation, which in turn leads to an overall decrease in crack resistance upon SiO₂ addition. Our work shows that, although pure silica glass has very high glass transition temperature and relatively high hardness, its addition in oxide glasses does not necessarily lead to significant increase in these properties due to the complex structural interactions in mixed network former glasses and the competitive effects of free volume and network rigidity.     

Grain boundary engineering that induces ultrahigh permittivity and decreased dielectric loss in CdCu3Ti4O12 ceramics

Dielectric materials with ultrahigh permittivity are attracting attention due to the increasing demand for these types of materials for microelectronics and energy storage applications. In this work, we successfully synthesized Zn-doped CdCu₃Ti₄O₁₂ (CdCTO) ceramics with low dielectric loss and large permittivity via an ordinary mixed-oxide technique. Remarkably, at a Zn doping level of 0.10, a CdCu_2.9Zn_0.1Ti₄O₁₂ ceramic exhibited both decreased dielectric loss tangent of ~0.058 and large dielectric permittivity > 4.0 × 10⁴, as well as a good frequency stability over a wide frequency range from 40 Hz to 10⁶ Hz. The high dielectric performance was attributed to the enhanced grain boundary resistance and internal barrier layer capacitor (IBLC) effect due to the fine and uniform grains that formed upon Zn doping. The findings reported in this work provide valuable insights into how to simultaneously realize a low dielectric loss and high permittivity in CdCTO and other related dielectric ceramics.     

Indentation cracking and deformation mechanism of sodium aluminoborosilicate glasses

Developing less brittle oxide glasses is a grand challenge in the field of glass science and technology, as it would pave the way toward new glass applications and limit the overall raw material usage and energy consumption. However, in order to achieve this goal, more insight into the correlation between the chemical composition and material properties is required. In this work, we focus on the mechanical properties of quaternary sodium aluminoborosilicate glasses, wherein systematic changes in glass chemistry yield different resistances to indentation crack initiation. We discuss the origin of the composition dependence of indentation cracking based on an evaluation of the deformation mechanism taking place during the indentation event. To this end, we use a simple metric, the extent of indent side length recovery upon annealing, to quantify the extent of reversible volume deformation. Finally, we also compare the compositional trend in crack initiation resistance to that in crack growth resistance (fracture toughness), showing no simple correlation among the two.     

聚能切割销毁废旧炮弹

根据本次要销毁的炮弹壁较厚等特点,经方案对比与论证,选用了线性聚能切割器对其进行爆炸销毁。本文介绍了线性聚能切割器参数设计的依据,切割器外形、药型罩以及炸药种类的选择,零炸高的实现,以及起爆网路、安全警戒及安全距离的计算;同时,阐述了利用聚能切割技术销毁废旧炮弹的效果和体会。     

塔里木灌区水库群实时调度研究

为缓和塔里木灌区引水与塔里木河的综合治理这一矛盾,以大系统分解协调技术与动态规划相结合的方法为基础建立了适合本灌区的自适应实时调度模型。为灌区水库实际控制应用提供了理论依据,对塔河的治理具有重要的现实意义。     

一类多体系统的非完整运动规划最优控制

研究一类带有非完整约束的多体系统运动规划问题。由于非完整约束的存在,运动规划和控制问题比一般的多体系统要困难得多。讨论了非完整系统的特性及可控性条件,利用无限维优化和控制理论,结合非完整控制系统特性,以系统耗散能量为性能指标,给出一类非完整运动规划的最优数值方法。最后将该方法用于自由漂浮空间双臂机器人,仿真结果实现了该类非完整系统的运动规划。     

绝缘子污秽的微波辐射特性研究

为较好地了解绝缘子上污秽的分布,根据微波辐射特性,提出了基于污秽物在微波波段的辐射特性差异来检测绝缘子绝缘状况的方法,其原理是绝缘子上有污秽物时发射率会随着污秽量和污秽性质变化导致辐射计的输出变化。在实验室中通过测量涂污绝缘子在污、湿环境中的天线温度,可得到等值盐密与天线温度的对应关系,从而可依据测量的天线温度去对应绝缘子的污秽程度。结果表明,绝缘子的污秽程度与天线温度有着较严格的对应关系。这种污秽量、水气与天线温度的确定关系,为准确监测绝缘子的污秽状况提供了理论依据,特别是对于污秽物与水共同作用,导致绝缘强度降低,造成污闪的现象,这种方法更接近实际工况。     

10 GHz再生锁模光纤激光器获得光纤超连续谱的研究

报道了利用10GHz再生锁模光纤环形激光器（RML-FRL）获得波长在1528～1563nm连续可调、脉宽为4．6～5．8ps的短脉冲输出作为高稳定的光纤超连续（SC）谱泵浦源。对RML-FRL输出的脉冲直接放大泵浦4．5km色散位移光纤（DSF）,得到20dB带宽46．08nm的SC谱输出,经阵列波导光栅（AWG）谱切片后,得到间隔100GHz、中心波长符合ITUT标准的30信道输出,脉宽在6．5～7．8ps,示波器显示任意信道的抖动均值小于1．4ps。     

电厂冷却水管化学镀Ni-Co-P/PTFE复合镀层及其防垢耐蚀性能

在电厂冷却水管常用的20#钢表面化学镀Ni-Co-P镀层,并以沉积速率作为指标,通过单因素实验得到化学镀Ni-Co-P镀层较优的溶液成分和工艺条件.在此基础上,通过向溶液中添加PTFE制备出Ni-Co-P/PTFE复合镀层,进一步研究了PTFE浓度对Ni-Co-P/PTFE复合镀层防垢耐蚀性能的影响.结果表明,随着PT...     

A New UKF Based Fault Detection Method in Non-linear Systems

To detect the bias fault in stochastic non-linear dynamic systems, a new Unscented Kalman Filtering（UKF） based real-time recursion detection method is brought forward with the consideration of the flaws of traditional Extended Kalman Filtering（ EKF）. It uses the UKF as the residual generation method and the Weighted-Sum Squared Residual （WSSR） as the fault detection strategy. The simulation results are provided which demonstrate better effectiveness and a higher detection ratio of the developed methods.