Fabrication and properties of lightweight SiOC fiber-based assembly aerogels with hierarchical pore structure

Here we report a novel aerogel material assembled by the electrospun SiOC fibers with a hierarchical pore structure. The fibrous aerogels were successfully fabricated by the gel-casting and freeze-drying method using the SiOC fibers as the matrix and the silica sols as the binders. The effect of the SiOC fiber content and the silica sol content on the properties of the samples were investigated. The SiOC fibrous aerogels after calcined at 1000?°C exhibited low densities of 46.87–128.48?mg/cm³, low thermal conductivities of 0.0302–0.0440?W/m?K, high compressive strengths of 18–167?kPa and relatively high specific surface areas of 12.48–34.87?m²/g. Such unique fibrous aerogel materials are foreseen as the promising high-temperature insulators, absorbents and supports.     

Diagnostic of capacitively coupled radio frequency plasma from electrical discharge characteristics: comparison with optical emission spectroscopy and fluid model simulation

The capacitively coupled radio frequency(CCRF)plasma has been widely used in various fields.In some cases,it requires us to estimate the range of key plasma parameters simpler and quicker in order to understand the behavior in plasma.In this paper,a glass vacuum chamber and a pair of plate electrodes were designed and fabricated,using 13.56 MHz radio frequency(RF)discharge technology to ionize the working gas of Ar.This discharge was mathematically described with equivalent circuit model.The discharge voltage and current of the plasma were measured atdifferent pressures and different powers.Based on the capacitively coupled homogeneous discharge model,the equivalent circuit and the analytical formula were established.The plasma density and temperature were calculated by using the equivalent impedance principle and energy balance equation.The experimental results show that when RF discharge power is 50–300 W and pressure is 25–250 Pa,the average electron temperature is about 1.7–2.1 e V and the average electron density is about 0.5?×?10~(17)–3.6?×?10~(17)m~(-3).Agreement was found when the results were compared to those given by optical emission spectroscopy and COMSOL simulation.     

Statistical modeling of mains zero crossing variation in powerline communication

In this paper, authors investigate statistical modeling of measured mains Zero Crossing (ZC) non idealities in narrowband powerline communication systems (PLC) using time series approach based on autoregressive moving average model (ARMA). For this purpose, Box Jenkins analysis steps are deployed for detected ZC impulsive variations. Estimated models exhibit a good fit based on R-square metric reaching 90%. This modeling approach is extended to three measurement environment: in home, in lab and rural locations. Obtained models are useful for NB-PLC channel emulator implementation.     

基于加速退化数据的航空液压泵剩余寿命预测技术研究

航空液压泵是航空装备的关键件之一。如何很好地预测液压泵的剩余寿命,使得液压泵的有效寿命能够得到更加充分合理地利用,将具有很大的理论价值和经济效益。通过研究某型航空液压泵的失效模式、失效机理和退化参数,确定其加速退化试验方案,建立其加速退化模型,并在此基础上建立了一套基于加速性能退化试验数据的航空液压泵剩余寿命预测方法及步骤,并以该型航空液压泵的加速性能退化试验数据为例对其剩余寿命进行了预测,验证了该方法的正确性和有效性。     

航空发射装置片簧失效分析

工厂在修理飞机时,发现航空发射装置片簧断裂。本文通过外观检查、断口形貌观察、组织及硬度检查等方法,对断裂的片簧进行了分析。结果显示,片簧失效模式为氢致延迟和机械疲劳复合断裂。结合片簧的表面处理及其使用过程,分析认为不正常的表面处理及飞行中的振动均为导致片簧失效的重要因素。     

一个分布式数据采集系统的设计与研制

对现有的数据采集系统结构与性能进行研究后,设计了模块式数据采集盒和分布式数据采集系统结构.该系统利用网络技术,将采样、监控计算机和独立的数据采集盒连接起来,实现多现场、多通道实时数据的监控、采集与处理.给出了系统总体结构、数据采集盒原理与设计、系统软件功能设计和系统实现方案.采集频率达到每通道每秒1～30 次,可同时采样5 000通道、监控2 000通道,兼有模拟仿真与数据处理功能.     

Influence of stress on the stray field signals of ferromagnetic materials

To investigate the influence of stress alone on the stray field signals of ferromagnetic materials, the static tensile tests of 0.45%C steel and 45CrNiMoVA steel fiat-shaped specimens were performed on an MTSSI0 hydraulic testing machine. Hp(y) signals,the normal component of spontaneous stray field, were measured during the testing process by an EMS-2003 metal magnetic mem-ory diagnostic apparatus cooperated with a non-magnetic electric control displacement instrument. Fracture and microstructure were observed by a scanning electronic microscope and a transmission electron microscope, respectively. The relationships between axial applied stress or residual stress measured by X-ray diffraction method and Hp(y) were analyzed. The results indicate that some regu-lar pattern of the magnetic curve is displayed only between applied stress and stray field signals. The magnetic ordering process stops due to dislocation pinning magnetic domain structure, and Hp(y) value unvaried nearly with applied load increasing in the plastic de-formation stage.     

真空渗流法制备泡沫铝及其动态力学性能的研究

以真空渗流法制备陶瓷中空球泡沫铝,研究了应变率对吸能量和吸能效率的影响、相对密度对屈服强度的影响,并与普通泡沫铝进行比较。结果表明,工艺简单可行,所制备的泡沫铝的动态压缩应力-应变曲线只有弹性变形区和塑性变形区;随应变率的增大,屈服强度和吸能效率变化规律不明显,吸能量增大;随相对密度的增大,屈服强度增大,吸能量增大,吸能效率也增大;动态压缩时两种泡沫铝的吸能效率均较高,最大吸能效率大于0.9,是良好的吸能材料。     

Q235钢静载拉伸过程中的磁记忆信号变化特征分析

选取Q235钢进行静载拉伸试验，利用EMS2003型磁记忆检测系统进行各级应力水平的检测。结果显示弹性极限范围内磁场强度曲线形貌接近未加载时，进入屈服阶段后磁场强度值明显增加，过零点数目在静载拉伸过程中呈现无规律变化，但弹塑性加载阶段均出现了过零点逼近最终断裂处的现象。该试验表明进入塑变后材料的组织结构变化与其所表现出的表面磁场强度值之间必然存在着某种对应关系，为磁记忆检测的进一步研究奠定了基础。     

干扰条件下雷达探测距离的建模和分析

雷达的一个重要指标是雷达探测目标的距离，采用表示平均单个脉冲信噪比和接收机匹配损耗对检测距离的影响的检测因子，可使检测距离的计算过程简化，由此建立的干扰条件下雷达作用距离的数学模型，可对自卫干扰和远距离支援干扰同时存在情况进行干扰距离的计算，并可分析雷达采用反干扰措施如低旁瓣、频率捷变对雷达检测距离提高的效能。