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991.
为探究硫酸盐干湿循环作用下带冷缝混凝土受荷作用时的能量演化规律,制作了整浇和浇筑间隔0.25 d、0.5 d、1 d、7 d和28 d的带冷缝混凝土,基于单轴压缩实验及能量计算原理,研究了硫酸盐干湿循环对带冷缝混凝土强度和能量演化规律的影响。结果表明:带冷缝混凝土强度及损伤应力和峰值应力处弹性应变能与耗散能均随干湿循环呈先增大后减小的趋势,随着新混凝土与母体浇筑间隔的增加呈现减小的趋势;随着干湿循环次数的增加,损伤应力处储能水平Kad先减小后增加,说明损伤应力处储能水平越高,带冷缝混凝土越容易产生损伤,Kad可以作为混凝土破坏的预警指标。 相似文献
992.
二甲苯是一种重要的人为源 VOC, 也是城市地区 SOA 的重要前体物。二甲苯光氧化形成的 SOA 受多种环
境因素影响, 而 NH3 对该反应形成的 SOA 生成产率及反应机制的影响尚不清楚。基于室内烟雾箱模拟系统, 探讨了
NH3 对二甲苯光氧化形成 SOA 质量浓度、物理特性及化学组成的影响。研究表明, 在低浓度条件下, NH3 对二甲苯
光氧化生成 SOA 具有明显的促进作用, 结合气溶胶质谱结果发现 NH3 促进醛酮类物质进入颗粒相以及含氮有机物的
生成是导致 SOA 质量浓度增加的主要原因。此外, NH3 能够提高邻二甲苯生成 SOA 的吸光度, 但是对对二甲苯无明
显影响。分析表明, 相较于对二甲苯, 邻二甲苯光氧化会生成大量醛类物质, NH3 与醛类发生美拉德反应是导致 SOA
吸光性增加的主要原因。 相似文献
993.
针对现有基于深度学习的林业昆虫图像检测方法存在检测精度低和检测速度慢的问题,提出一种结合改进PANet结构与三分支注意力机制的目标检测方法YOLOv4-TIA。通过对样本数量较少的昆虫类别进行数据增强,实现样本均衡分布。利用三分支注意力机制改进YOLOv4中的CSPDarkNet53骨干网络,同时通过旋转操作和残差变换建立维度间的依存关系,以提高有效的特征通道权重,在PANet结构上增加将跳跃连接与跨尺度连接相结合的特征融合方式,从而获取更丰富的语义信息和位置信息。在此基础上,采用Focal loss函数优化分类损失,解决正负样本不均衡的问题。实验结果表明,该方法的精确率和召回率分别达到85.9%和91.2%,相比SSD、Faster R-CNN、YOLOv4方法,其在保证检测速度的同时,能够有效提高检测精度,且实现对林业害虫的实时精确监测。 相似文献
994.
Machining of 17-4 Precipitation Hardenable Stainless Steel (PH SS) is one of the difficult tasks because of its high cutting temperatures. Conventional cutting fluids are used to overcome the high cutting temperatures, but these are not acceptable from the health and environmental sustainable points of view. Cryogenic cooling is one of the potential techniques to overcome such problems. In the current work, comparison is made of cryogenic turning results, such as tool flank wear, cutting forces (feed force, main cutting force), cutting temperature, chip morphology and surface integrity characteristics with wet machining during machining of heat-treated 17-4 PH SS. The result showed that in cryogenic machining, a maximum of 53%, 78%, 35% and 16% reductions was observed in tool flank wear, cutting temperature, surface roughness and cutting force, respectively, when compared with wet machining. It was also evident from the experimental results that cryogenic machining significantly improved the machining performance and product quality even at high feed rates. 相似文献
995.
996.
Ying Chen Yan-qing Dong Zhe Yan Dong Chen Yong Chen Lu-hui Wang 《Fullerenes, Nanotubes and Carbon Nanostructures》2017,25(6):363-370
Carbonization of magnetic polymer microspheres is one of the methods for the preparation of magnetic carbon materials. Fe3O4 magnetic particle characteristics considerably influence the magnetic content and size distribution of magnetic polymer microspheres. The characteristics of Fe3O4 nanoparticles modified by oleic acid (OA) and undecylenic acid (UA) were analyzed by X-ray diffraction, Fourier transform infrared, scanning electron microscopy, dynamic laser light scattering, thermogravimetry/differential thermogravimetry, vibrating sample magnetometer, and water contact angle. Fe3O4 nanoparticles modified by OA and UA are nearly spherical and exhibit superparamagnetism. Fe3O4 particle size and saturation magnetization are slightly influenced by the OA and UA composition. OA and UA both are chemically adsorbed onto Fe3O4 as bidentate chelates. OA shows easier adsorption onto Fe3O4 than UA. OA groups have an expanded arrangement on OA@Fe3O4, whereas UA groups have a condensed arrangement on UA@Fe3O4. Particle lipophilicity decreases and particle clustering increases with decreasing OA content and increasing UA content on OA-UA@Fe3O4 nanoparticles. 相似文献
997.
Zhonghai Song Ning Cao Xuejiao Gao Qiu Liang 《Fullerenes, Nanotubes and Carbon Nanostructures》2017,25(2):65-70
Ultrathin Co3O4 nanosheets grown on the reduced graphene oxide (Co3O4/rGO) was synthesized by a simple hydrothermal method and was investigated as a cathode in a Li-O2 battery. Benefited from the synergistic effect between Co3O4 and rGO, the hybrid exhibits a high initial capacity of 10,528 mAh g?1 along with a high coulombic efficiency (84.4%) at 100 mA g?1. In addition, the batteries show an enhanced cycling stability and after 113 cycles, the cut-off discharge voltage remains above 2.5 V. The outstanding performance is intimately related to the high surface area of rGO, which not only provide carbon skeleton for the uniform distribution of Co3O4 nanosheets but also facilitate the reversible formation and decomposition of insoluble Li2O2. The results of electrochemical tests confirm that the Co3O4/rGO hybrid is a promising candidate for the Li-O2 batteries. 相似文献
998.
Photonic Reactions Leading to Fluorescence in a Polymeric System Induced by the Photothermal Effect of Magnetite Nanoparticles Using a 780 nm Multiphoton Laser
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Bum Chul Park Hee‐Dae Kim June Park Yu Jin Kim Young Keun Kim 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(37)
Recently, polymer‐coated magnetite (Fe3O4) nanoparticles (NPs) are extensively studied for applications in therapeutics or diagnostics using photothermal effect. Therefore, it is essential to understand the interactions between Fe3O4 NPs and polymers when optical stimuli are applied. Herein, the photonic reactions of Fe3O4 NPs and polymer composites upon application of a 780 nm multiphoton laser are analyzed. The photonic reactions produce unique results including fluorescence from conformationally changed polymer and low‐temperature phase transformation of Fe3O4 NPs. Typically, π‐conjugated chains are formed, inducing fluorescence through a series of main and side‐chain cleavage reactions of polymers with the aliphatic chain. In addition, fluorescence is detected in the cellular system by photonic reactions between Fe3O4 NPs and biomolecules. After multiphoton laser irradiation, light emission is detected near the intracellular Fe3O4 NPs, and a stronger intensity is observed in large‐sized NPs. 相似文献
999.
Fabrication of Fe3O4 Dots Embedded in 3D Honeycomb‐Like Carbon Based on Metallo–Organic Molecule with Superior Lithium Storage Performance
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Chengfei Li Liuqing Li Zhaopeng Li Weihao Zhong Zhenghui Li Xiaoqing Yang Guoqing Zhang Haiyan Zhang 《Small (Weinheim an der Bergstrasse, Germany)》2017,13(38)
A novel metallo–organic molecule, ferrocene, is selected as building block to construct Fe3O4 dots embedded in 3D honeycomb‐like carbon (Fe3O4 dots/3DHC) by using SiO2 nanospheres as template. Unlike previously used inorganic Fe3O4 sources, ferrocene simultaneously contains organic cyclopentadienyl groups and inorganic Fe atoms, which can be converted to carbon and Fe3O4, respectively. Atomic‐scale Fe distribution in started building block leads to the formation of ultrasmall Fe3O4 dots (≈3 nm). In addition, by well controlling the feed amount of ferrocene, Fe3O4 dots/3DHC with well‐defined honeycomb‐like meso/macropore structure and ultrathin carbon wall can be obtained. Owing to unique structural features, Fe3O4 dots/3DHC presents impressive lithium storage performance. The initial discharge and reversible capacities can reach 2047 and 1280 mAh g?1 at 0.05 A g?1. With increasing the current density to 1 and 3 A g?1, remarkable capacities of 963 and 731 mAh g?1 remain. Moreover, Fe3O4 dots/3DHC also has superior cycling stability, after a long‐term charge/discharge for 200 times, a high capacity of 1082 mAh g?1 can be maintained (80% against the capacity of the 2nd cycle). 相似文献
1000.
Uniform ordered mesoporous ZnCo2O4 nanospheres for super-sensitive enzyme-free H2O2 biosensing and glucose biofuel cell applications 总被引:1,自引:0,他引:1
Cui Shiqiang Li Li Ding Yaping Zhang Jiangjiang Wu Qingsheng Hu Zongqian 《Nano Research》2017,10(7):2482-2494
Uniform,ordered mesoporous ZnCo2O4 (meso-ZnCo2O4) nanospheres were successfully synthesized using a sacrificing template method.The meso-ZnCo2O4 nanospheres were used for the first time for H2O2 biosensing and in glucose biofuel cells (GBFCs) as an enzyme mimic.The meso-ZnCo2O4 nanospheres not only exhibited excellent catalytic performance in the H2O2 sensor,achieving a high sensitivity (658.92 μA·mM-1·cm-2) and low detection limit (0.3 nM at signal-to-noise ratio (S/N) =3),but also performed as an excellent cathode material in GBFCs,resulting in an open circuit voltage of 0.83 V,maximum power density of 0.32 mW·cm-2,and limiting current density of 1.32 mA·cm-2.The preeminent catalytic abilities to H2O2 and glucose may be associated with the large specific surface area of the mesoporous structure in addition to the intrinsic catalytic activity of ZnCo2O4.These significant findings provide a successful basis for developing methods for the supersensitive detection of H2O2 and enriching catalytic materials for biofuel cells. 相似文献