High energy storage and ultrafast discharge in NaNbO3-based lead-free dielectric capacitors via a relaxor strategy

Dielectric capacitors with decent energy storage and fast charge-discharge performances are essential in advanced pulsed power systems. In this study, novel ceramics (1-x)NaNbO₃-xBi(Ni_2/3Nb_1/3)O₃(xBNN, x = 0.05, 0.1, 0.15 and 0.20) with high energy storage capability, large power density and ultrafast discharge speed were designed and prepared. The impedance analysis proves that the introducing an appropriate amount of Bi(Ni_0·5Nb_0.5)O₃ boosts the insulation ability, thus obtaining a high breakdown strength (E_b) of 440 kV/cm in xBNN ceramics. A high energy storage density (W_total) of 4.09 J/cm³, recoverable energy storage density (W_rec) of 3.31 J/cm³, and efficiency (η) of 80.9% were attained in the 0.15BNN ceramics. Furthermore, frequency and temperature stability (fluctuations of W_rec ≤ 0.4% over 5–100 Hz and W_rec ≤ 12.3% over 20–120 °C) were also observed. The 0.15BNN ceramics exhibited a large power density (19 MW/cm³) and ultrafast discharge time (~37 ns) over the range of ambient temperature to 120 °C. These enhanced performances may be attributed to the improved breakdown strength and relaxor behavior through the incorporation of BNN. In conclusion, these findings indicate that 0.15BNN ceramics may serve as promising materials for pulsed power systems.     

Study on heat conduction and adsorption/desorption characteristic of MIL-101/few layer graphene composite

Journal of Porous Materials - Aiming at the poor heat conduction performance of porous MIL-101 applied in adsorption cooling process, few layer graphene (FLG) was selected as a promising thermal...     

Cu-5％Fe合金薄板带的研制与应用

利用非真空感应熔炼、半连续铸造及电磁搅拌的方式,实现了Cu-5％Fe合金锭的制备,并通过现代化的成套轧制设备,实现了Cu-5％Fe合金薄板带的制备;采用金相显微镜、维氏硬度计、万能试验机等测试了其显微组织、力学性能、导电率等.另外,对Cu-5％Fe合金薄带的电磁屏蔽性能进行测试,结果显示:在14 kHz～18 GHz频率范围内,Cu-5％Fe合金的屏蔽效能都能达到60 dB(除14 kHz外)以上,可以作为军用设备的屏蔽材料.     

PAN/FPU Composite Nanofiber Membrane with Superhydrophobic and Superoleophobic Surface as a Filter Element for High-Efficiency Protective Masks

Recently, because of the outbreak of COVID-19, the demand for various types of filter elements in protective materials has increased globally. Furthermore, new requirements for the filtration performance of PM2.5 liquid (oil) particles have been put forward. In this work, Superhydrophobic and superoleophobic composite nanofibers with excellent filtration capacity for oil and salt particles are developed through the modification of polyacrylonitrile (PAN) by fluoro-polyurethane (FPU) doping. The results show that the PAN/FPU composite nanofibers doped with 9 wt% FPU has a uniform fiber morphology with a diameter of 240 ± 30 nm. Compared to the pure PAN nanofibers, the water-based contact angle of PAN/FPU increases from 90 ± 5° to 151 ± 5°, and the oil-based contact angle increases from 58 ± 2° to 152 ± 3°. Importantly, at a high flow rate of 95 L min⁻¹, the filtration efficiency of the PAN/FPU nanofiber membrane for 0.3 µm oil particles increases from 92 ± 1% to 99.2 ± 0.1%. After cyclic loading, the filtration efficiency of 0.3 µm oil particles remains above 98%. Meanwhile, the filtration efficiency for 0.3 µm salt particles remains at 98.23 ± 0.1%. The PAN/FPU nanofiber membrane developed in this work is effective in applications and has good market prospects as a protective filtration material.     

电导法测定水的全盐量

采用电导法研究了水溶液中盐的浓度与其电导率的关系，根据模拟水样和实际水样在电导率与全盐量的关系上有较好的吻合性，介绍了电导法测定水中全盐量的方法，结果表明在低浓度范围内电导率与盐浓度成线性关系，与传统的重量法相比，具有快速、简便、准确度高的特点。     

计算机网络技术与安全管理维护探析

随着计算机网络的不断发展,计算机网络技术也得到了很大程度的提高。计算机网络存在开放性的特点,然而正是由于计算机网络的开放性,使得计算机在进行数据传输、存储的过程中受到了安全方面的威胁。本文主要对影响计算机网络安全的因素进行分析,并对计算机网络技术与安全管理维护措施进行探讨,旨在提高计算机网络的安全性。     

攻击型无人机鲁棒导引律研究

文章研究了攻击型无人机鲁棒导引系统,采用对干扰和摄动具有自适应能力的滑动模态变结构控制方法设计了攻击型无人机滑模导引规律.针对用于消除颤振的伪滑动模态不能实现精确跟踪的缺陷,对滑模导引规律中颤振消除进行了优化设计,引入系统运动状态轨迹接近角变量,使消除颤振的伪滑动模态边界层宽度随着系统状态到达滑动模态而逐渐减小为零,从而达到了既能消除颤振又能实现精确跟踪的设计目标.通过仿真验证了该导引规律具有攻击弹道平缓、抗目标机动扰动能力强、鲁棒性好、制导精度高的优点.     

基于改进灰色关联算法的雷达反隐身能力评估

针对复杂电磁环境下雷达获取隐身目标特性存在不完整性、多样性等特点,提出一种基于改进灰色关联算法和距离优化评估模型的雷达反隐身能力评估方法.该方法针对一般的主观权重可靠性不足的缺点,依据指标的主观、客观和关联属性实时计算并修正了指标权值.建立了基于性能与作战效能的雷达反隐身能力评估指标体系,并结合样本序列的稳定程度和指标值的优劣程度给出了雷达反隐身能力的优化评估距离,得出客观、准确的评估结果.理论分析和仿真试验表明,与一般的灰色关联算法相比,复合权重的灰色关联算法具有更好的系统评估能力和更高的准确性.     

Ce3+/Tb3+-coactived NaMgBO3 phosphors toward versatile applications in white LED,FED, and optical anti-counterfeiting

Ce³⁺/Tb³⁺ co-doped NaMgBO₃ phosphors were successfully synthesized by solid-state method. Under 381 nm excitation, the cyan emission owing to the 5d → 4f of Ce³⁺ ions and green emissions arising from the ⁵D₄ → ⁷F_J (J = 6, 5, 4, and 3) transitions of Tb³⁺ ions were seen in all the phosphors. Through theoretical analysis, one knows that the energy transfer from Ce³⁺ to Tb³⁺ ions with high efficiency of 83.74% was contributed by dipole–dipole transition. Furthermore, the internal quantum efficiency of NaMgBO₃:0.01Ce³⁺,0.03Tb³⁺ phosphor was 54.28%. Compared with that of at 303 K, the emission intensity of the developed products at 423 K still kept 73%, revealing the splendid thermal stability of the studied phosphors. Through utilizing the resultant phosphors as cyan-green components, the fabricated white-LED device exhibited an excellent correlated color temperature of 2785 K, high color-rendering index of 85.73, suitable luminance efficiency of 25.00 lm/W, and appropriate color coordinate of (0.4279, 0.3617). Aside from the superior photoluminescence, the synthesized phosphors also exhibited excellent cathode-luminescence properties which were sensitive to the current and accelerating voltage. Furthermore, the NaMgBO₃:0.01Ce³⁺,0.03Tb³⁺ phosphors with multi-mode emissions were promising candidates for optical anti-counterfeiting. All the results indicated that the Ce³⁺/Tb³⁺ co-doped NaMgBO₃ phosphors were potential multi-platforms toward white-LED, field emission displays, and optical anti-counterfeiting applications.     

基于VxWorks时钟特性的无人机飞行数据抗干扰方法研究及实现

为解决当无人机受到干扰时,飞行数据采集异常情况从而导致无人机无法正常工作的情况,文章提出了一种适合无人机系统使用基于VxWorks并行时钟工作特性的无人机飞行数据抗干扰方法;并给出关键技术的研究途径和工程实现方法;经理论分析,本方法有效的解决无人机飞行数据的抗干扰问题;最后通过飞行实验数据表明本方法抗干扰性能良好,并且不会对无人机系统的硬件设计和实时性产生影响,可应用在无人机系统设计中。