基于目标级联技术的含风电互联电网机组组合策略

针对含风电互联电网日前安全约束机组组合的规模大、约束复杂、求解困难等问题,提出基于目标级联分析技术的分散协调优化策略。将问题分解为负责区域间边界节点电压相角协调的上层优化问题和以并行方式独立优化各区域发电计划的下层优化问题。下层优化以弃风电量期望和电量不足期望,量化各区域内风电、负荷预测误差,以及常规机组强迫停运等系统运行不确定性所带来的风险,并以罚函数的形式引入目标函数,以综合优化系统可靠性与经济性。2区域12节点系统和IEEE RTS96三区域互联系统算例仿真验证所建模型和算法的有效性。     

Yellow resistant photosensitive resin for digital light processing 3D printing

Digital light processing (DLP) has been studied and developed in the field of three-dimensional (3D) printing in recent years due to its fast curing rate and high resolution. To reduce the cost and viscosity of the resin system, the aromatic polyurethane acrylates (PUAs) were used as oligomer. The matrix resin called PUH₂ consists of oligomers (PUA, bisphenol A polyoxyethylene ether dimethyl acrylate) and active diluents (hydroxyethyl acrylate, hydroxyethyl methacrylate). However, the photosensitive resin containing aromatic isocyanate groups was easily yellowed under ultraviolet light. In this article, we developed a resin for DLP 3D printing with yellowing resistance, excellent mechanical properties and high heat resistance. The optimal ratio of 3DP-PUH₂ resin was PUH₂/TPO/RYOJI-292/dye/nanosilica = 100/5/0.4/0.01/0.1, and its viscosity was 500 cp, which is suitable for DLP 3D printing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48369.     

机制砂混凝土耐磨性的主要影响因素分析及多因素计算模型

本文研究了砂类型、砂率、石粉含量和抗压强度对机制砂混凝土耐磨性的影响,建立了磨损量的多因素计算模型。结果表明:由于含石粉及具有更高的粗糙度和坚固性,石灰岩与辉绿岩机制砂制备的C30、C40混凝土耐磨性比河砂混凝土提高20%以上;在0.40~0.44范围内选取较低的砂率可获得较优的耐磨性;利用石粉含量为5%~11%(质量分数)的机制砂制备混凝土,石粉含量为9%时可获得最佳的混凝土耐磨性,微观分析表明此时混凝土密实度最佳;通过灰色系统理论确定了耐磨性影响因素的影响程度排序为:砂率R₃>压碎值R₂>粗糙度R₁>抗压强度R₅>石粉含量R₄>0.6;对比验证表明提出的混凝土磨损量多因素计算模型具有较高的预测精度和良好的适用性。     

Microwave dielectric ceramics in (Mg1/3Sb2/3)O2-ZrO2-TiO2 system with near zero τf and low loss in a very wide range

A series of (ZrTi)_1-x(Mg_1/3Sb_2/3)_2xO₄ (0.04?≤?x?≤?0.36) ceramics were successfully synthesized through the conventional solid-state processing. Appropriate content of CuO was added as sintering aids to promote the density of ceramics. The XRD analysis revealed that the main crystalline phase of ceramics sintered at optimal temperature belonged to α-PbO₂-type structure. Raman spectroscopy and far infrared reflectivity (FIR) spectra were employed to study the phonon modes of ceramics, which explained the relationship between microwave dielectric properties and structure. It is interesting that the τ_f are near-zero (+6.6 ~ ?4.6?ppm/°C) and meanwhile the Q×f are relatively high (29,000–41,800?GHz) for samples with x in a very wide range of 0.10–0.36. In this range, their dielectric constants (ε_r) can be adjustable from 35.4 to 24.4. The results demonstrated this ceramic system is a potential candidate for microwave dielectric applications requiring an adjustable dielectric constants and near zero τ_f.     

A fast approach to the synthesis of MO/CNT/Fe hybrid nanostructures built on MXene for enhanced Li-ion uptake

We report herein a fast and scalable approach to the synthesis of MO/CNT/Fe (MCI) hybrid nanostructures via microwave irradiation of MXene under ambient condition. The effect of three arcing materials, CNT, graphite (C), and carbon fiber (C_f), on the growth of carbon nanotubes on MXene-derived metal oxides were investigated. The resulted MCI nanostructures were tested as anodes in LIBs, all exhibiting better electrochemical performance than that of pristine Ti₃C₂. Remarkably, MCI-C_f delivered reversible capacities of 430?mA?h?g^?1 and 175?mA?h?g^?1 at 1?A?g^?1 and 10?A?g^?1, respectively, which is much higher than that of commercial graphite at high rates. The findings in this work open new exciting opportunities to developing hybrid electrode materials with high specific capacity for energy conversion and storage.     

Effects of structural characteristics on microwave dielectric properties of low-loss (Zn1-xNix)ZrNbTaO8 ceramics

Low-loss (Zn_1-xNi_x)ZrNbTaO₈ (0.02?≤?x?≤?0.10) ceramics possessing single wolframite structure are initiatively synthesized by solid-state route. Based on the results of Rietveld refinement, complex chemical bond theory is used to establish the correlation between structural characteristics and microwave performance in this ceramic system. A small amount of Ni²⁺ (x?=?0.06) in A-site with the fixed substitution of Ta⁵⁺ in B-site can effectually raise the Q?×?f value of ZnZrNb₂O₈ ceramic, embodying a dense microstructure and high lattice energy. The dielectric constant and τ_f are mainly affected by bond ionicity and the average octahedral distortion. The (Zn_0.94Ni_0.06)ZrNbTaO₈ ceramic sample sintered at 1150?°C for 3?h exhibits an outstanding combination of microwave dielectric properties: ε_r =?27.88, Q?×?f?=?128,951?GHz, τ_f =?–39.9?ppm/°C. Thus, it is considered to be a candidate material for the communication device applications at high frequency.     

High tunability in (1 1 0)-oriented BaZr0.2Ti0.8O3 (BTZ) lead-free thin films fabricated by pulsed laser deposition

Using a pulsed laser deposition method the BaZr_0.2Ti_0.8 O₃ (BTZ) lead–free thin films with a thickness of ~250 nm were grown on FTO, ITO and Pt–Si substrates, respectively. The analysis results of microstructural, dielectric properties and leakage current reveal that the thin films deposited on Pt–Si substrates are oriented growth along the (1 1 0) direction and exhibit the optimal performance characteristics. Calculations of figure of merit (FoM) and dielectric tunability display a maximum value of ~42.8 and ~68.5% at E = 400 kV/cm at room temperature, respectively. The excellent tunable properties, high dielectric constant (~635@ 100 kHz) and low leakage current density of (9.3 × 10^–8 A/cm² at 400 kV/cm) make the (1 1 0)–oriented BaZr_0.2Ti_0.8 O₃ thin film to be an attractive material for applications of tunable devices.     

Experimental study on gas–liquid dispersion and mass transfer in shear-thinning system with coaxial mixer

The effects of impeller type, stirring power, gas flow rate, and liquid concentration on the gas–liquid mixing in a shear-thinning system with a coaxial mixer were investigated by experiment, and the overall gas holdup, relative power demand, and volumetric mass transfer coefficient under different conditions were compared. The results show that, the increasing stirring power or gas flow rate is beneficial in promoting the overall gas holdup and volumetric mass transfer coefficient, while the increasing system viscosity weakens the mass transfer in a shearing–thinning system. Among the three turbines, the six curved-blade disc turbine (BDT-6) exhibits the best gas pumping capacity; the six 45° pitched-blade disc turbine (PBDT-6) has the highest volumetric mass transfer coefficient at the same unit volume power.     

Coexistence of three ferroelectric phases and enhanced piezoelectric properties in BaTiO3–CaHfO3 lead-free ceramics

Perovskite ferroelectrics possess the fascinating piezoelectric properties near a morphotropic phase boundary, attributing to a low energy barrier that the results in structural instability and easy polarization rotation. In this work, a new lead-free system of (1-x)BaTiO₃-xCaHfO₃ was designed, and characterized by a coexistence of ferroelectric rhombohedral-orthorhombic-tetragonal (R-O-T) phases. With the increase amount of CaHfO₃ (x), a stable coexistence region of three ferroelectric phases (R-O-T) exists at 0.06 ≤ x ≤ 0.08. Both large piezoelectric coefficient (d₃₃～400 pC/N), inverse piezoelectric coefficient (d₃₃^*～547 pm/V) and planar electromechanical coupling factor (k_p～58.2%) can be achieved for the composition with x = 0.08 near the coexistence of three ferroelectric phases. Our results show that the materials with the composition located at a region where the three ferroelectric R-O-T phases coexist would have the lowest energy barrier and thus greatly promote the polarization rotation, resulting in a strong piezoelectric response.