Structure and Photoluminescence of A Blue‐Green‐Emitting Phosphor for Near‐UV White LEDs

A series of phosphors Ca_12(0.97?x)Al₁₄O₃₂F₂: 0.03Ce³⁺, xTb³⁺ have been prepared by a hightemperature solid‐state reaction using boric acid as flux. These oxyfluorides crystallize in cubic structure, space group. Under the near ultraviolet excitation within wavelength range 310–390 nm, Ca_12(0.97?x)Al₁₄O₃₂F₂: 0.03Ce³⁺, xTb³⁺ phosphors exhibit an intense emission covering a broad band of 370–500 nm derived from the 5d→4f transitions of Ce³⁺ and a characteristic emission at 544 nm of Tb³⁺. The emission can be tuned from blue to green by altering the relative ratio of Ce³⁺ to Tb³⁺ in the composition. The energy‐transfer mechanism from Ce³⁺ to Tb³⁺ is investigated based on the site occupancy of the luminescence center in the crystal structure of the Ca₁₂Al₁₄O₃₂F₂ host. More importantly, when a certain amount of boric acid is added as flux in the synthesis, the fluorescence intensity of the phosphors increases about 65%. Because of its broad excitation and efficiently tunable blue to green luminescence, the Ca_12(0.97?x)Al₁₄O₃₂F₂: 0.03Ce³⁺, xTb³⁺ phosphors may find promising application as a near UV‐convertible phosphor for white‐light‐emitting diodes.     

自动铺丝构件缺陷形成机理的研究进展

自动铺丝是一种重要的复合材料自动化成型方法,可实现连续变角度铺放,适合大曲率复杂构件的制造,但成型质量受到了多种工艺参数的影响。本文从自动铺丝预浸料的粘弹性和流动性、结晶度、铺层的层间剪切强度、残余热应力以及最大弯曲力等方面对自动铺丝构件成型缺陷的形成进行了表征和机理分析;给出了影响构件成型缺陷的工艺参数,并总结了工艺参数优化方法的研究进展。最后,对自动铺丝构件成型缺陷形成机理的未来研究方向进行了展望。     

Influence of tip end-plate on noise of small axial fan

In this work, tip end-plate is used to improve the noise performance of small axial fans. Both numerical simulations and experimental methods were adopted to study the fluid flow and noise level of axial fans. Four modified models and the prototype are simulated. Influences of tip end-plate on static characteristics, internal flow field and noise of small axial fans are analyzed. The results show that on basis of the prototype, the model with the tip end-plate of 2 mm width and changed length achieved best noise performance. The overall sound pressure level of the model with the tip end-plate of 2 mm width and changed length is 2.4 dB less than that of the prototype at the monitoring point in specified far field. It is found that the mechanism of noise reduction is due to the decrease of vorticity variation on the surface of blades caused by the tip end-plate. Compared with the prototype, the static pressure of the model with the tip end-plate of 2 mm width and changed length at design flow rate decreases by 2 Pa and the efficiency decreases by 0.8%. It is concluded that the method of adding tip end-plate to impeller blades has a positive influence on reducing noise, but it may diminish the static characteristics of small axial fan to some extent.     

Microstructure and sliding wear behavior of pseudo-alloy PS45/CuAl8 composite coating sprayed by HVAA technique

A pseudo-alloy PS45/CuAl8 composite coating was sprayed on steel substrate by high-velocity activated arc spraying (HVAA) process. Its sliding wear behavior at room temperature was evaluated by M-2000 wear tester. For comparison, a single CuAl8 coating was also prepared and tested under the same conditions. It is found that the pseudo-alloy composite coating consists of α-Cu and γ-Ni metallic matrix phases together with homogenously distributed minor Al 2 O 3 , Cr 2 O 3 oxide phases. Moreover, pseudo-alloy coating possesses much better sliding wear resistance than CuAl8 coating due to the enhanced hardness and microstructural homogenization. Fatigue wear and abrasive wear are responsible for the wear-down mechanism of the pseudo-alloy coating.     

关于自由基聚合几个值得关注的问题

总结了自由基聚合教学中的几个值得关注的问题,包括自由基聚合时不同引发剂类型的选择和确定、聚合温度及其区间选择及确定、聚合时间的确定、溶剂选择等。同时阐述了这些相关因素在自由基聚合研究方案设计时的相互关系。旨在使学生对自由基聚合的认识更为深刻和系统,培养学生独立进行自由基聚合研究方案设计的能力。     

民机地形感知警告系统前视功能分析及仿真

综述了民机地形感知警告系统(TAWS)及其前视功能的产生背景、发展过程,介绍了TAWS前视功能的主要原理.对前视功能的报警阈值时间设置方法进行了研究,给出了报警阈值时间设置的分析算法模型,并利用Matlab 工具进行了仿真,得到了相应的仿真结果.最后,对进一步提高TAWS前视功能仿真精确度,以及TAWS产品性能优化方法...     

Microstructure and sliding wear behavior of pseudo-alloy PS45/CuA18 composite coating sprayed by HVAA technique

A pseudo-alloy PS45/CuAl8 composite coating was sprayed on steel substrate by high-velocity activated arc spraying (HVAA) process. Its sliding wear behavior at room temperature was evaluated by M-2000 wear tester. For comparison, a single CuAl8 coating was also prepared and tested under the same conditions. It is found that the pseudo-alloy composite coating consists of α-Cu and γ-Ni metallic matrix phases together with homogenously distributed minor A12O3, Cr2O3 oxide phases. Moreover, pseudo-alloy coating possesses much better sliding wear resistance than CuA18 coating due to the enhanced hardness and microstructural homogenization. Fatigue wear and abrasive wear are responsible for the wear-down mechanism of the pseudo-alloy coating.     

复合材料纤维缠绕成型CAD/CAM相关技术研究

纤维缠绕成型是制造高强度复合材料制品的一种重要的工艺方法，将CAD／CAM方法应用其中可以大大提高生产效率，降低设计成本。本文提出了纤维缠绕CAD／CAM系统的总体方案，并对其中缠绕数学模型、线型优化、丝嘴轨迹生成等量要组成部分进行了分析与研究，为CAD／CAM系统的开发奠定了理论基础。     

建筑结构动力时程响应分析与计算的新方法

基于状态空间理论分析与计算结构动力时程响应问题,根据结构动力学方程,引入结构系统的状态变量,建立结构动力时程响应分析的状态方程,并给出非齐次状态方程的解。对于求解矩阵指数函数有多种解法,着重介绍了凯莱哈密尔顿法、状态空间迭代法和精细积分法。对结构动力时程响应问题按三种解法分别建立了计算格式,并编制了相应计算程序。给出若干数值算例,其计算结果表明,状态空间法分析计算结构动力时程响应精度好、效率高,是一种非常有效的方法。     

单减速器起升机构浮式起重机主钩穿绳工艺

结合韩国三星重工8 000 t浮式起重机主钩缠绕穿绳方案,研究了单减速器式起升机构穿绳方案的关键工艺技术。实践证明,新工艺技术成功解决了8 000 t浮式起重机主钩穿绳问题,并节省大量人力资源,取得了较大的经济效益。