Co-precipitation synthesis of ZnAl2O4: Cr3+ phosphor for better light penetration in pc-LED

Cr doped ZnAl₂O₄ spinel samples were prepared by the traditional solid state reaction and co-precipitation synthetic route, and the results suggest that the co-precipitation method has some superiority in contrast to the solid state reaction method. XRD, FT-IR, and XPS spectra confirmed that the well-crystallized spinel cubic phase of ZnAl₂O₄: Cr³⁺ samples were successfully formed. The morphology of the samples was investigated by FE-SEM and FE-TEM, and the results show that the samples by the co-precipitation route can generate a smaller size of particles compared to the solid state reaction. Photoluminescence excitation spectra monitored at 686 nm are comprised of two broad excitation bands near 530 nm and 395 nm, and the emission spectra show emissions ranging from 640 to 780 nm, due to the ²E?→?⁴A₂ spin-forbidden transition of Cr³⁺ ions in spinel lattices. The optimized concentration monitored at 686 nm is 1%, while at 693 nm is 3.5%. Compared with the samples by solid state reaction method, the samples by co-precipitation method show preferable luminescent properties, such as the higher photoluminescence intensity and higher quantum efficiency. Several phosphor-converted LEDs were to investigate the applicability of the prepared samples. The results confirm that the phosphor has potential applications in plant growth and supplementing the red region in white-LEDs and the phosphors prepared by co-precipitation are more suitable to be used in phosphor-converted LED devices due to their preferable luminescent properties.

     

不凝性气体对溴化锂吸收式制冷机组的影响及其预防管理

分析了机组不凝性气体的来源,并阐述其对机组的不利影响.介绍了机组气密性管理和真空度管理的方法.     

Comparison of a novel MPN method against the yeast extract agar (YEA) pour plate method for the enumeration of heterotrophic bacteria from drinking water

This study compared the Quanti-Disc most probable number (MPN) test for heterotrophic bacteria from drinking water with the widely used yeast extract agar (YEA) pour plate method. The Quanti-Disc test module contains 50 reaction wells in which a medium has been pre-deposited. The medium contains a suite of three fluorogenic enzyme substrates selected for the detection of enzymes expressed widely by heterotrophic bacteria. The MPN of heterotrophic bacteria is calculated from the number of fluorescing reaction wells after incubation of a sample. Quanti-Disc and the YEA pour plate method were compared according to guidance on comparing methods given in United Kingdom national guidance and ISO 17994:2004. The two methods were also challenged with reference strains and isolates of heterotrophic bacteria from drinking water. This indicated that heterotrophic bacteria commonly encountered in drinking water are detected by both the YEA pour plate method and Quanti-Disc. Analysis of data from split water samples (723 for 37 degrees C tests and 872 for 22 degrees C tests) from nine geographically diverse laboratories in England and Wales demonstrated that the Quanti-Disc method is equivalent to the YEA pour plate method for the analysis of heterotrophic bacteria from drinking and similar waters at 37 degrees C, and superior to YEA for the analysis at 22 degrees C. The Quanti-Disc method is a simple and efficient alternative method for the enumeration of heterotrophic bacteria from drinking water.     

结构-设备耦合体系地震响应振动台试验研究

工业建筑中设备与结构存在复杂的动力相互作用,不同动力特性的结构与设备组成的耦合体系其地震响应也会发生变化。为了研究结构-设备耦合体系在参数变化时的地震响应和破坏过程,进行了三个耦合体系模型的振动台试验。模型由钢筋混凝土框架结构和钢结构单自由度振子组成。试验得到了结构-设备耦合体系在地震波作用下的动力特性、位移反应、动力放大系数、动应变和层间滞回耗能。分析了质量比和频率比参数变化对耦合体系地震响应的影响。研究表明,随着质量比的增大,结构地震反应增大,设备地震反应减小;随着频率比的减小,结构地震反应减小,设备地震反应增大。研究结果可为支承设备的结构动力设计提供参考。     

Influence of sintering temperature on the crystallization and mechanical properties of BN-MAS composites

A type of boron nitride–magnesium aluminum silicate (BN-MAS) composite ceramics was fabricated by hot-press sintering at different sintering temperatures. The relationship between the sintering temperature and microstructure was investigated by analyzing the interaction between hexagonal boron nitride (h-BN) and the MAS phase. The main MAS phase in the composite ceramics is the α-cordierite phase at a sintering temperature of 1300°C. At temperatures above 1400°C, the inhibitory effect of h-BN on the crystallization of the MAS system is significant, and MAS mainly exists in the form of an amorphous phase. The composite sintered at 1700°C exhibited the highest bending strength of 218MPa. h-BN and MAS were co-enhanced. MAS can be used as an effective liquid-phase sintering aid to assist in the sintering of h-BN, whereas h-BN can absorb the fracture energy of the composite ceramics through the pull-out and bridging effect of the particles.     

基于微纳层叠技术的聚合物纳米纤维制备及应用研究进展

简述了微纳层叠共挤技术的发展;总结了近些年来基于微纳层叠技术制备纳米纤维的研究进展,包括聚合物参数,制备方法和成纤机理;对目前几种典型微纳层叠成纤方法进行了分类和对比,并对纤维的性能进行了阐述;对微纳层叠纳米纤维的应用进行了介绍。最后针对微纳层叠技术用于纳米纤维制备的发展方向和应对的挑战进行了浅析。     

熔体微分静电纺PBAT纤维膜的制备工艺研究

探究了聚己二酸对苯二甲酸丁二醇酯（PBAT）熔体静电纺性能,并研究了熔体微分静电纺工艺参数与PBAT纤维性能之间的关系。结果表明,随着纺丝温度的升高,纤维直径减小,纤维直径分布呈先减小后增大的趋势;随着纺丝电压的升高,纤维直径减小且分布均匀,纤维膜力学性能逐渐提高;当纺丝距离为9 cm,纺丝温度为260 ℃,纺丝电压为45 kV时,制备的纤维细度及均匀度最佳,其直径为4.31 μm,直径分布标准差为0.76,纤维膜拉伸强度为9.9 MPa、断裂伸长率为111.2 %。     

A novel photochromic material based on halophosphate: Remote light-controlled reversible luminescence modulation and fluorescence lifetime regulation

Luminescent material Ca₂Ba₃(PO₄)₃F:Eu²⁺ displays green emitting in the range of 400–700?nm, which is ascribed to the 4f⁶5d¹ →4f⁷ transition of Eu²⁺ ions. Amazingly, the body color of the samples can be changed between colorless and green upon alternative UV and visible light irradiation/heating treatment with robust fatigue resistance due to photochromism. The photochromic effect strongly depends on the Eu²⁺ doping concentration. After remote-controlled short-UV irradiation, the overall Eu²⁺ emission intensity presents a significant decrease, and inversely, exhibits an increase to the initial level after illuminated by longer wavelength light or heat treatment. Moreover, the fluorescence lifetime also can be regulated reversibly, of which the regulation degree depends on the short-UV irradiation and longer wavelength illumination time/heating temperature. A schematic diagram based on energy levels is proposed to illustrate the photochromism mechanism.     

理论分析光偏振对导光管光传输效率的影响

光传输效率(LTE)是衡量导光管采光性能的最重要参数。在导光管LTE计算中，常常忽略了光线在管中若干次镜面反射引起的光偏振的累积效应。因此，为厘清连续镜面反射引起光偏振的累积效应，通过光学理论分析与公式推导，在确定光偏振对镜面反射材质反射率的影响之后，首次揭示了导光管内壁反射率随反射次数的变化规律，以及反射率的变化对导光管LTE的影响。结果表明：单束自然光线每投射到管内壁一次，就会产生一次光偏振，并在两个正交分量上产生不同的反射率，即ρ_⊥和ρ_‖,且ρ_⊥≥ρ_‖;历次反射中ρ_⊥和ρ_‖数值保持不变，但整体反射率会随反射次数增多而逐渐变大，故导光管内光损速率会不断减缓；由此提出了导光管中单束光线的LTE表达式，为建立复杂光源下LTE数学计算模型，奠定了理论基础。     

Water filtration properties of novel composite membranes combining solution electrospinning and needleless melt electrospinning methods

New composite polyvinyl alcohol (PVA)/polypropylene (PP) membranes were prepared by combining both solution electrospinning and melt electrospinning methods. Self‐designed and made needleless melt electrospinning device was used to fabricate PP membranes which acted as the support layer. PVA membrane on the surface was fabricated via solution electrospinning. The electrospun PVA/PP composite membranes were characterized by the pore size distribution, pure water flux, and rejection ratio, then compared with general composite membranes. Characterizations revealed that the fiber diameter of solution electrospun PVA membrane and melt electrospun PP membrane were 0.171 ± 0.027 and 2.24 ± 0.33 μm, respectively, and the average pore size was 0.832 μm and 27.29 μm, which was much smaller than the nonwoven membrane. The rejection ratio to the 500 nm particles of the PVA/PP composite membrane could reach more than 96%, which was much larger than that of the PVA/non‐woven substrate of 90%, and the melt electrospun PP membrane of 80%, and still maintained high permeate flux of 32,346 L/m²h under the pressure of 0.24 bar. This approach of compositing the solution electrospun membranes and melt electrospun membranes could be useful in designing novel microfiltration membrane owning both higher flux and higher rejection ratio. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41601.