Nanosized NaA zeolite was successfully synthesized by hydrothermal method using tetraethyl orthosilicate (TEOS) and aluminum isopropoxide (AIP) as the main raw materials. The surface modification of NaA zeolite was carried out by silane coupling agent 3-aminopropyltriethoxysilane (KH-550). The effects of silane coupling agent dosage, reaction temperature, reaction time, hydrolysis time and pH value on grafting rate of NaA zeolite were investigated in detail. The zeolites were characterized by XRD, SEM-EDS, FT-IR and TG-DTA. The results showed that the surface of NaA zeolite was modified successfully by KH-550. The optimal modification conditions obtained were as follows: the dosage of coupling agent in 95 % ethanol – 1.6 %, reaction temperature − 70 °C, reaction time – 2 h, hydrolysis time – 20 min, and pH value – 3.5. Under these conditions, the grafting rate of modified NaA zeolite was 3.95 %.
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Firstly, a single-axis FBG accelerometer with intensity modulation-direct detection interrogation system was put forward and designed in the paper. Experiments with different excitation frequencies were implemented, which demonstrate its good mechanical structure and fabrication technology. Accordingly, a novel tri-axis FBG accelerometer based on the single-axis FBG accelerometer was proposed and a series of periodic vibration tests were finished to prove its performance at different excitation frequencies. The response of the tri-axis vector FBG accelerometer can keep up with the increasing excitation frequency with good signal-to-noise ratio (SNR) within 160 Hz. The suitable measurement frequency range of the accelerator is between 0 and 500 Hz. The cross-axis response among three axes is analyzed. These experiments indicate that horizontal axes have less influence on the vertical axis vibration of FBG.
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We investigate the effects of higher-order space charge field on the self-deflection of bright screening spatial solitons due to two-photon photorefractive effects by a numerical method under steady-state conditions. The expression for an induced space charge electric field including higher-order space charge field terms is obtained. Numerical results indicate that bright screening solitons undergo self-deflection process during propagation, and the solitons always bend in the opposite direction of the c axis of the crystal. The self-deflection of bright screening solitons can experience considerable increase especially in the regime of high bias field strengths. Relevant examples are provided.
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