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991.
A new rhodamine-based derivative bearing a naphthyridine group (compound 1) was synthesized as a colorimetric and fluorescent “off-on” chemosensor for Cu2+ in aqueous solutions. The sensing behaviors of 1 toward various metal ions in neutral aqueous solutions were investigated by absorption and fluorescence spectroscopies. Compound 1 is found to exhibit a significant increase in absorbance at 561 nm and an amplified fluorescence at 590 nm toward Cu2+ in a selective, sensitive and rapid manner. The quantification of Cu2+ by 1 using an absorption spectroscopy method was satisfactory in the linear working range 0.9–10 μM, with a detection limit of 5.4?×?10?8?M for Cu2+ and good tolerance of other metal ions. Upon addition of Cu2+, the spirolactam ring (colorless and nonfluorescent) of 1 was opened to ring-opened amide (red color and fluorescent) and a 1:1 stoichiochemetry for the 1-Cu2+ complex was formed with an association constant of 1.57?×?104?M?1. 相似文献
992.
Wen-Jeng?HsuehEmail author Ren-Zheng?Qiu Chang-Hung?Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(1):27
Occurrence of resonant transport due to Fabry-Perot like effect through cascade double asymmetric rings is proposed. We find that high performance reflectors with wide bands can be generated by two asymmetrical open rings with an arm ratio of 1/3. At the resonances, giant persistent currents exist in both rings of the system. The resonance energy is variant and dependent on the length of the connected wire. However, the confined space of the system at the resonance is not equal to the integral multiple of a half-wavelength of traditional Fabry-Perot etalons. 相似文献
993.
Existence of the perfect transmission resonances of spin waves in a one-dimensional Thue–Morse magnonic quasicrystal is proposed. We find that occurrence of the perfect transmission just corresponds to the repeated bandedges in the bandedge map. Frequencies at the perfect transmissions for system with arbitrary generation order can be predicted by the bandedge map of the second and third order systems using two iterative schemes. These results show that density of the perfect transmission resonance increases exponentially for increasing the order of the system. However, the perfect transmissions are kept for higher order systems even if the peaks become denser. 相似文献
994.
应用磁控共溅射技术和后退火方法制备了GaAs/SiO2纳米颗粒镶嵌薄膜,并分别应用原子力显微镜、X射线衍射和卢瑟福背散射实验来观测薄膜的形貌、相结构和化学组分.结果表明GaAs纳米颗粒的平均直径很小(约为1.5~3.2nm),且均匀地分布于SiO2之中,薄膜中的GaAs和SiO2组分都符合化学计量关系.应用脉冲激光高斯光束对薄膜的光学非线性进行了Z扫描测试和分析.结果表明,薄膜的三阶光学非线性折射率系数和非线性吸收系数都由于量子限制效应而大大地增强,在非共振条件下,它们分别约为4×10-12m2/W和2×10-5m/W,在准共振的条件下,它们分别约为2×10-11m2/W和-1×10-4m/W. 相似文献
995.
996.
997.
Qifeng Han Chenghong Duan Changjian Ji Kai Qiu Fei Zhong Xinhua Li Zhijun Yin Xiancun Cao Xiuju Zhou Yuqi Wang 《Journal of Electronic Materials》2008,37(8):1058-1063
Self-seeded aluminum nitride (AlN) crystals were successfully grown in a tungsten crucible by the sublimation method. The
polarities along the growth direction of these AlN samples were characterized by chemical etching, combined with high-resolution
transmission electronic microscopy (HRTEM) and Raman spectroscopy. It has been proven by our experimental results that etching
in KOH solution and in molten KOH-NaOH can be a reliable method to determine the surfaces with different polarities. Chemically
active N-polar (0001) AlN surfaces were removed appreciably, while only etch pits related to threading dislocations were observed
on Al-polar surfaces after chemical etching. HRTEM images revealed that there are noticeable inversion domain boundaries in
the samples. Raman spectrum measurements showed the vibration mode change before and after etching in the same geometrical
arrangement. 相似文献
998.
999.
可以使用多片1-wire总线器件DS18B20构成多点测温系统,因此,如何准确、有效地对每一温度传感器进行寻址成为该系统设计的一个核心问题。文中提出如下方案:首先分别读出探测单元有单个DS18B20的ROM序列号;然后将其存放在I^2C总线的EEPROM存储器AT24C16中,并将其编号贴在温度传感器表面,对于一个探测单元有多个不可分离的DS18B20的ROM序列号的读取,只有利用DS18B20特有的单线网络自动搜索功能得到;最后,将所有温度传感器接入温度测量网络,与AT24C16中已经存储的ROM号匹配,实现每片DS18B20的寻址和温度测量功能,将测量的温度值送LED(发光二极管)显示或者通过RS-485总线送计算机处理。 相似文献
1000.
Qiu Weihong Mercer S. Liang Zhixiang Miller G. 《Power Electronics, IEEE Transactions on》2008,23(1):163-171
Driver dead-time control is a popular scheme used to prevent the occurrence of the shoot-through issue in a synchronous Buck voltage regulator. As the switching frequency is continually increasing in today's converter design, the deadtime interval is now long enough relative to the switching period to impact the system performance. In addition to its impact on efficiency, driver dead-time also impacts loop gain and system stability, especially under the critical load condition. In this paper, the influence of driver dead time on the synchronous buck converter is investigated in detail. With voltage mode control, the system loop gain will change under different load conditions due to the deadtime impact. The deadtime may cause sub-harmonic current ripple in the voltage regulator with sample-and-hold current mode control, while its impact on the peak current mode control can be ignored. Design equations are provided to avoid this issue. Some analysis data are included and compared to experimental results. 相似文献