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The simplified model for 4f-5d transitions is applied to obtain the line strengths for emission, ground-state absorption and excited states absorption involving 4f-5d transitions of Nd3+ in crystals. The results are host independent for the usual case where 5d crystal-field interaction can be considered as strong, in the sense that the calculated 5d-4f emission relative line strengths will be the same for Nd3+ in any host. Also the calculated 4f-5d absorption line strengths can be grouped by the 5d crystal-field components. For each 5d crystal-field component, the group of absorption line strengths for different 4f25d transition final states forms a pattern independent of the 5d crystal-field component and the host. For practical cases, due to strong but still limited 5d crystal-field splitting, the transitions to different 5d crystal-field components may overlap each other. The theoretical results are used to interpret available experimental data. 相似文献
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材料超声回波衰减是评价材料均匀一致性的常用方法, 针对具有复杂结构的航空发动机盘件难以进行材料底面超声回波衰减评价的问题, 本文提出了利用超声背散射波信号直接预测底面回波衰减的方法。采用10MHz聚焦探头进行超声背散射波数据的采集, 利用深度学习技术构建和训练模型,建立了基于深度学习的材料底面回波衰减预测方法, 同时讨论了采用不同信号形式的超声波信号分类识别模型的准确率差异。研究发现:基于深度学习技术可实现通过超声背散射波预测材料的底面回波衰减, 预测结果和实际底面回波衰减试验结果具有良好的一致性。 相似文献
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航空发动机中的后轴颈锻件一般采用水浸超声纵波直入射方法检测内部缺陷。由于型面结构的问题,在锻件的直筒和锥形段连接区域存在检测盲区。该文针对某型号发动机中的后轴颈锻件,开展了水浸超声检测工艺研究,提出利用小角度纵波覆盖盲区的思路。通过对含有人工缺陷的模拟样件的检测实验,比较了水浸纵波直入射和小角度纵波斜入射两种检测方法对后轴颈连接区域的覆盖能力。结果表明,该文提出的小角度纵波方法,可以有效检测出水浸纵波直入射检测方法无法发现的人工缺陷,消除由结构引起的检测盲区,保障零件的服役安全。 相似文献
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Pd-catalyzed annulation of aryne and aryl ketone O-acetyloxime via C–H bond activation was realized. Through the C–H bond activation/insertion/cyclization/elimination reaction sequence, phenanthridines are successfully constructed, providing an attractive strategy to approach substituted heterocycle without preactivation of starting materials. 相似文献
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Guan Wu ;Ran Ran ;Bote Zhao ;Yujing Sha ;Chao Su ;Yingke Zhou ;Zongping Shao 《天然气化学杂志》2014,(3):363-375
Amorphous carbon and graphene co-modified LiFePO_4 nanocomposite has been synthesized via a facile polyol process in connection with a following thermal treatment.Various characterization techniques,including XRD.Mossbauer spectra,Raman spectra,SEM,TEM,BET,O_2-TPO,galvano charge-discharge,CV and EIS were applied to investigate the phase composition,carbon content,morphological structure and electrochemical performance of the synthesized samples.The effect of introducing way of carbon sources on the properties and performance of LiFePO_4/C/graphene composite was paid special attention.Under optimized synthetic conditions,highly crystalized olivine-type LiFePO_4was successfully obtained with electron conductive Fe_2P and FeP as the main impurity phases.SEM and TEM analyses demonstrated the graphene sheets were randomly distributed inside the sample to create an open structured LiFePO_4 with respect to graphene,while the glucosederived carbon mainly coated over LiFeP04 particles which effectively connected the graphene sheets and LiFePO_4 particles to result in a more efficient charge transfer process.As a result,favorable electrochemical performance was achieved.The performance of the amorphous carbon-graphene co-modified LiFePO_4 was further progressively improved upon cycling in the first 200 cycles to reach a reversible specificcapacity as high as 97 mAh·g~(-1) at 10 C rate. 相似文献
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This article reports on the synthesis of a novel amphiphilic polyhedral oligomeric silsesquioxane (POSS) end-capped poly(2-(2-methoxyethoxy)ethyl methacrylate)-co-oligo(ethylene glycol) methacrylate) (POSS-P(MEO2MA-co-OEGMA)). These thermoresponsive organic–inorganic hybrid polymers exhibit critical phase transition temperature in water, which can be finely tuned by changing the feed ratio of OEGMA and MEO2MA. The lower critical solution temperature (LCST) of POSS-P(MEO2MA-co-OEGMA) increases from 31 to 59 °C with the increasing of OEGMA content. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies show that these polymers can self-assemble into spherical micelles with the thermosensitive block into the corona and the POSS forming the core, and larger aggregates are formed when the temperature values are above their LCSTs. These thermoresponsive polymers POSS-P(MEO2MA-co-OEGMA) with self-assembly behavior and tunable tempetature-responsive property have the potential applications in material science and biotechnology. 相似文献