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81.
The acoustic radiation characteristics of free-flooded ring transducers made of PZT4 and PMN-PT materials are calculated and compared.First,the theoretical formulae for free-flooded ring transducers are studied.The resonant frequencies of a transducer made of PZT4 and PMN-PT materials are calculated.Then,the transmitting voltage responses of the free-flooded ring transducers are calculated using the finite element method.Finally,the acoustic radiation characteristics of the free-flooded ring transducers are calculated using the boundary element method.The calculated results show that the resonant frequencies of the free-flooded ring transducer made of PMN-PT are greatly reduced compared with those made of PZT4 with the same size.The transmitting voltage response of the transducer made of PMN-PT is much higher than that of the transducer made of PZT4.The calculated 3-dB beamwidth of the acoustic radiated far-field directivity of the free-flooded ring transducer made of PZT4 at the resonant frequency 1900 Hz is 63.6 and that of the transducer made of PMN-PT at the resonant frequency 1000 Hz is 64.6.The comparison results show that the free-flooded ring transducer made of PMN-PT material has many advantages over that made of PZT4.The PMN-PT is a promising material for improving the performance of free-flooded ring transducers. 相似文献
82.
Structure and photoluminescence properties of Er3+-doped TiO2-SiO2 powders prepared by sol-gel method 下载免费PDF全文
Er 3+-doped TiO 2-SiO 2 powders are prepared by the sol-gel method,and they are characterized by high resolution transmission electron microscopy (HR-TEM),X-ray diffraction (XRD) spectra,and Raman spectra of the samples.It is shown that the TiO 2 nanocrystals are surrounded by an SiO 2 glass matrix.The photoluminescence (PL) spectra are recorded at room temperature.A strong green luminescence and less intense red emission are observed in the samples when they are excited at 325 nm.The intensity of the emission,which is related to the defect states,is strongest at the annealing temperature of 800 C.The PL intensity of Er 3+ ions increases with increasing Ti/Si ratio due to energy transfer between nano-TiO 2 particles and Er 3+ ions. 相似文献
83.
A method based on magnetic moment measurement to identify the structural transition of quenched Fe1 -xGax (x = 0.15ben 0.30) alloys 下载免费PDF全文
A method based on the measurement of Fe average atomic magnetic moment to identify the structural transition caused by the increase of Ga content in quenched Fe1 - xGax alloys (0.15 ≤ x ≤ 0.30) is proposed. The quenched Fe1 - xGax alloys show a change of the Fe average atomic magnetic moment from 2.25 μB to 1.78 μB and then to 1.58 μB, which corresponds to the structural transition from A2 to D03 and then to B2. The relationship between the structure and the magnetostriction is clarified, and the maximum magnetostriction appears in the A2 phase. The variation tendency of the magnetostriction is well characterized, which also reflects the structural transition. 相似文献
84.
在自反的严格凸的光滑Banach空间中给出了一种关于拟φ-非扩张映像族的公共不动点的新混杂算法,并利用广义投影算子和K-K性质等技巧证明了该算法的强收敛性.所得结果是近期相关结果的改进与推广. 相似文献
85.
采用电位平均表面增强拉曼散射(PASERS)新方法研究二巯基嘧啶(2MP)在不同电极电位下与银电极的作用,PASERS 谱的获得是在快速调制两个电极电位的同时记录 SERS 谱。研究表明2MP在—1.1V 以正的电极电位下,通过硫原子以竖立方式作用于银电极表面,在—1.1V 以负的电位下发生电化学还原反应。 相似文献
86.
本文发展了Schommers的时间观点,定义了时间,尤其是表征量子系统光散射的散射时间和共振散射时间。通过散射时间本征态的假定实现了散射时间的量子化,得到了量子化的共振散射时间。对原子的弹性光散射和Raman散射的成功应用推出了原子和原子的价电子逐级电离所形成的离子的所有原子能级的普适近似公式。 相似文献
87.
本文讨论一类广义形式的H—方程解的存在性,推广了某些已知的结果,并用所得结果讨论了L_(p)(G)空间中的H—积分方程解的存在性。 相似文献
88.
本文对非参数多元回归模型Y~(j)(x_(in))=g(x_(in))+e~(j)(x_(in))中误差序列{e~(j)(x_(in)),j≥1}为m_0—相依序列和局部广义高斯序列时,给出未知函数g(x)的估计量的相合性。 相似文献
89.
90.