跨声速离心压气机机匣处理扩稳研究

高增压技术是高升功率车用内燃机的主要技术瓶颈之一,其核心难点在于高压比离心压气机内部复杂跨声速流动导致稳定运行范围窄,无法满足车用工况在高压比条件下对稳定运行工作范围的要求。为拓宽跨声速离心压气机的稳定工作范围,利用全三维数值模拟研究了机匣处理几何参数对扩稳的作用规律及机理。试验结果表明,采用优化后的机匣处理结构,压气机稳定工作范围由20.8%提高到33.6%。     

变化基本图形生长关键能力——通过数学实验变化四边形进行单元教学的尝试

核心素养是我们课堂教学内容的指引,关键能力则是对教学目标的具体要求,单元探究学习是以学生的自主学习为主,以教师的引导为主线,以优化学生的综合能力为主脉,是实现深度学习、为课堂教学赋能的有效教学方式、方法.笔者将单元教学和动手做实验的学习方式相结合进行了一次尝试.在学生已经完成平行四边形、菱形、矩形正方形的判定学习,并且...     

(∈,∈∨ q(λ,μ))-模糊强正则子半群

本文是正则半群的模糊化研究工作的继续,首先给出了广义模糊强正则子半群的概念,其次基于模糊点理论给出了(∈,∈∨ q(λ,μ))-模糊强正则子半群的概念,并且讨论了它们的相关性质.最后获得了(∈,∈∨ q(λ,μ))-模糊强正则子半群的同态像与同态原像的有关性质.     

Effect of fused silica subsurface defect site density on light intensification

The effect of defect density on the modulation of incident laser waves is investigated. First, based on the actual defect distribution in the subsurface of fused silica, a three-dimensional (3D) grid model of defect sites is constructed. The 3D finite-difference time-domain method is developed to solve the Maxwell equations. Then the electrical field intensity in the vicinity of the defect sites in the subsurface of fused silica is numerically calculated. The relationships between the maximal electrical field intensity in fused silica and the geometry of the defect sites are given. The simulated results reveal that the modulation becomes more remarkable with an increase of the defect density. In addition, the effect of the distribution mode of defects on modulation is discussed. Meanwhile, the underlying physical mechanism is analyzed in detail.     

Role of chelating agent in chemical and fluorescent properties of SnO2 nanoparticles

A modified polyacrylamide gel route is applied to synthesize SnO2 nanoparticles. High-quality SnO2 nanoparticles with a uniform size are prepared using different chelating agents. The average particle size of the samples is found to depend on the choice of the chelating agent. The photoluminescence spectrum detected at λex = 230 nm shows a new peak located at 740 nm due to the surface defect level distributed at the nanoparticle boundaries.     

Synthesis and Characterization of ZnO Nanoflowers Grown on AlN Films by Solution Deposition

ZnO nanoflowers are synthesized on AlN films by solution method. The synthesized nanoflowers are composed of nanorods, which are pyramidal and grow from a central point, thus forming structures that are flower-shaped as a whole. The nanoflowers have two typical morphologies： plate-like and bush-like. The XRD spectrum corresponds to the side planes of the ZnO nanorods made up of the nanoflowers. The micro-Raman spectrum of the ZnO nanoflowers exhibits the E2 （high） mode and the second order multiple-phonon mode. The photoluminescence spectrum of the ZnO nanoflowers exhibits ultraviolet emission centred at 375nm and a broad green emission centred at 526 nm.     

溶胶-凝胶SiO2薄膜氨热两步后处理

 以正硅酸乙酯为前驱体,氨水作催化剂,采用溶胶-凝胶法提拉镀制SiO₂双面膜,对薄膜进行氨处理和热处理。采用椭偏仪、分光光度计、红外光谱、扫描探针显微镜、静滴接触角测量仪表征薄膜的特性。研究表明：经氨热两步后处理,膜厚持续减小,折射率经氨处理先增大了0.236,再经热处理又减小了0.202,膜层透光性变好,透过率峰值持续向短波方向移动;经两步后处理的膜面平整度明显变好,与水的接触角先增大到58.92°后减小到38.07°。     

Comprehensive performance of a ball-milled La0.5Pr0.5Fe11.4Si1.6B0.2Hy/Al magnetocaloric composite

Due to the hydrogen embrittlement effect, La(Fe,Si)₁₃-based hydrides can only exist in powder form, which limits their practical application. In this work, ductile and thermally conductive Al metal was homogeneously mixed with La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2 using the ball milling method. Then hydrogenation and compactness shaping of the magnetocaloric composites were performed in one step via a sintering process under high hydrogen pressure. As the Al content reached 9 wt.%, the La_0.5Pr_0.5Fe_11.4Si_1.6B_0.2H_y/Al composite showed the mechanical behavior of a ductile material with a yield strength of ~44 MPa and an ultimate strength of 269 MPa accompanied by a pronounced improvement in thermal conductivity. Due to the ease of formation of Fe-Al-Si phases and the several micron and submicron sizes of the composite particles caused by ball milling process, the magnetic entropy change of the composites was substantially reduced to ~1.2 J/kg· K-1.5 J/kg· K at 0 T-1.5 T.     

通过金属有机小分子水凝胶选择性形成实现磷酸根的可视识别

利用磷酸根和钳型三联吡啶锌络合物的金属中心锌离子具有选择性配位的能力,通过金属有机水凝胶的选择性形成实现了对磷酸根的可视识别.在此基础上,利用一系列实验对这类金属有机水凝胶的热稳定性、流变性质、外观样貌进行了详细表征和分析之后提出了对磷酸根选择性识别的可能机理.     

酯交换反应对PBT/PC/Al_2O_3复合材料导热性能的影响

以聚对苯二甲酸丁二醇酯(PBT)与双酚A型聚碳酸酯(PC)为基体、氧化铝(Al2O3)作为导热填料,通过熔融共混法制备了PBT/PC/Al_2O_3导热复合材料,采用亚磷酸三苯酯(TPPi)作为酯交换反应抑制剂调节材料中树脂基体的相态结构,并通过红外光谱分析(FTIR)、激光导热仪、扫描电子显微镜(SEM)、示差扫描量热仪(DSC)及力学性能测试仪等对材料中的酯交换反应、导热性能、相态结构、结晶参数及力学性能进行了表征.实验结果表明,TPPi的加入可有效抑制体系中酯交换反应的发生,使PBT/PC共混物的相态结构改变,进而对填料的分布状态产生影响.当PBT/PC配比为1/1时,向其中加入1 wt%的TPPi可使体系的相态结构趋向于形成双连续相态结构,并有效提升材料的导热系数;在该体系中加入60 wt%的Al_2O_3后,材料的导热系数达到0.89 W/(m·K),相对于未加入TPPi的相同体系提升了13%.