Distorted wave response of ultrasonic annular stator incorporating non-uniform geometry

The traveling wave ultrasonic stator is normally fabricated with teeth. The tooth geometry improves the driving speed, but it creates natural frequency splitting and mode contamination, especially a distorted traveling wave. A dynamic model of a stepped-plate periodic stator is developed to examine the distortion. The stator is treated as an annular supported by a thin mid plate, and the support stiffness is formulated by using equivalent energy principle. The effects of the tooth and mid plate on the natural frequency and vibration mode are examined by using the perturbation method. The rules governing the frequency splitting, frequency perturbation as well as mode contamination are also identified. The traveling wave response and elliptical trace on stator surface are obtained by using the mode superposition method and they are proved to be distorted due to the tooth geometry. The response at the repeated doublets becomes coupled forward and backward traveling waves, but that at the split doublets becomes coupled forward traveling, standing and backward traveling waves. The results indicate that the tooth mass instead of the stiffness decreases the vibration amplitude and driving speed of the dominant wave, but their effects are different at the repeated and split doublets. Inspection of the model implies that the distortion can be suppressed by using a suitable combination of the wavenumber, tooth count, tooth height and occupying fraction. Numerical calculations are carried out to demonstrate the tooth geometry effect on the transient waveform, driving speed and elliptical trace. The optimization of the tooth geometry that can help achieve a purer traveling wave is discussed.     

Liquid hydridosilane precursor prepared from cyclopentasilane via sonication at low temperatures without the action of light

We report on a liquid hydridosilane precursor ink prepared via the ultrasonically induced ring-opening polymerisation of cyclopentasilane (Si₅H₁₀) without irradiation by ultraviolet light. The sonication is carried out in N₂ atmosphere at temperatures between 20 and 75 °C. We use size exclusion chromatography (SEC) to show polymer growth and estimate molecular mass with increasing sonication time. In combination with UV–vis transmission measurements, further SEC analysis is used to compare solutions subjected to either purely thermal or ultrasonic treatment at the same process temperature and for the same duration. Our findings provide strong evidence showing that the initiation of the polymerisation is sonocatalytic in nature and not thermic due to the macroscopic temperature of the solution. The liquid precursor is used to produce homogeneous hydrogenated amorphous silicon (a-Si:H) thin films via spin coating and pyrolytic conversion. The optoelectronic properties of the films are subsequently improved by hydrogen radical treatment. Fourier transform infrared spectroscopy (FTIR) is used to determine a compact film morphology and electrical conductivity measurements show that the layers attain a light-to-dark photosensitivity ratio of 2 × 10³ making them suitable for application in optoelectronic devices.     

Effect of ultrasound on the synthesis of low-modulus zeolites from a metakaolin

It was studied the effect of ultrasonic processing (22 kHz) of the aqueous suspension of metakaolin, sodium hydroxide and alumina with a molar ratio 2Al₂Si₂O₇:12NaOH:2Al₂O₃ on the low-modulus zeolite synthesis processes. To investigate the XRD, SEM, IR, EDS had been used. It was shown that after ultrasonic processing, sodium aluminates are formed, what leads to a change in process of further synthesis. It was found that without ultrasonic processing on the stage of thermal treatment at 650 °C, SOD zeolite (|Na₆|[Al₆Si₆O₂₄]) and sodium aluminosilicate (Na₆Al₄Si₄O₁₇) are synthesized. In the sample after ultrasound during thermal treatment, only sodium aluminosilicates of cubic syngony (Na₆Al₄Si₄O₁₇ and Na₈Al₄Si₄O₁₈) are formed. It was demonstrated that sodium aluminosilicates are precursors for the formation of LTA zeolite (|Na₁₂|[Al₁₂Si₁₂O₄₈]). As a result zeolitization of sodium aluminosilicates after the hydrothermal crystallization in alkaline solution, the sonicated sample contained 97 wt% LTA. Without ultrasonic processing, the product of synthesis contained 50 wt% SOD and 40 wt% LTA.     

连续臂丛神经阻滞镇痛对断指再植血流动力学影响的研究

目的研究连续臂丛神经阻滞镇痛对断指再植术后再植指血流动力学的影响，探讨其缓解血管痉挛、增加血流量的可行性。方法将60例急诊行断指再植术患者按随机数字表法分为术后连续臂丛神经阻滞镇痛组（CA组）和对照组（NA组），每组30例。观察两组患者再植指术后血管痉挛、血管栓塞和指体坏死发生例数并计算再植指成活率，记录两组术后即刻（T1）、术后24h（T2）再植指固有动脉血流动力学参数及动脉内径（AD）、远指端血氧饱和度（SpO2）和温度（Ts）变化。结果断指再植术后成活率CA组高于NA组，血管痉挛、血管栓塞和指体坏死发生率CA组均低于NA组，差异均有统计学意义（均P＜0.05）。在T2时CA组各项血流动力学参数、AD、SpO2、Ts均高于NA组，阻力指数（RI）低于NA组，差异均有统计学意义（均P＜0.05）。结论术后连续臂丛神经阻滞镇痛可以缓解再植指固有动脉痉挛，增加指体血流量，提高了断指再植的成功率。     

Weak coupling of a Reynolds model and a Stokes model for hydrodynamic lubrication

The Reynolds model is a reduced Stokes model, valid for narrow lubrication regions. In order to be able to handle locally non‐narrow regions such as pits or grooves, often displaying rapid geometrical variations, there is a need to be able to transit to the more accurate Stokes model. A fundamental problem is how to couple the two models in a numerical simulation, preferably allowing for different meshes in the different domains. In this paper, we present a weak coupling method for Reynolds and Stokes models for lubrication computations, including the possibility of cavitation in the different regions. The paper concludes with a numerical example. Copyright © 2010 John Wiley & Sons, Ltd.     

Determination of Pd,Rh, Pt,Au in road dust by electrothermal vaporization inductively coupled plasma mass spectrometry with slurry sampling

Inductively coupled plasma mass spectrometry coupled with ultrasonic slurry sampling electrothermal vaporization (USS-ETV-ICP-MS) has been applied to determine Pd, Rh, Pt and Au in 0.5% m/v slurries of several road dust samples. 2% m/v ammonium pyrrolidine dithiocarbamate (APDC) was used as the modifier to enhance the ion count. The influence of instrument operating conditions, slurry preparation and interferences on the ion count was reported. This method has been applied to the determination of Pd, Rh, Pt and Au in BCR 723 Road Dust and NIST SRM 2709 San Joaquin Soil reference materials and two road dust samples collected locally. The analysis results of the standard reference materials agreed with the certified values. Precision between sample replicates was better than 10% for all the determinations. The method detection limits estimated from standard addition curves were 0.9, 0.4, 0.6 and 0.4 ng g⁻¹ for Pd, Rh, Pt and Au, respectively, in original dust samples.     

Broadband dielectric characterization of piezoelectric poly(vinylidene fluoride)thin films between 278 K and 308 K

This work describes the dielectric properties of piezoelectric poly(vinylidene fluoride) (PVDF) thin films in the frequency and temperature ranges relevant for usual applications. We measured the isothermal dielectric relaxation spectra of commercial piezoelectric PVDF thin films between 10 Hz to 10 MHz, at several temperatures from 278 K to 308 K. Measurements were made for samples in mechanically free and clamped conditions, in the direction of the poling field (perpendicular to the film). We found that the imaginary part of the dielectric relaxation spectra of free and clamped PVDF samples is dominated by a peak, above 100 kHz, that can be characterized by a Havriliak-Negami function. The characteristic time follows an Arrhenius dependence on temperature. Moreover, the spectra of the free PVDF samples show two additional peaks at low frequencies which are associated with mechanical relaxation processes. Our results are important for the characterization of piezoelectric PVDF, particularly after the stretching and poling processes in thin films, and for the design and characterization of a broad range of ultrasonic transducers.     

基于ARM的嵌入式超声传播时间测量装置

应用超声波检测技术进行检测时,通常需对超声波在介质中的传播时间进行精准的测量,为精准测量超声波的传播时间,设计了一套基于ARM的嵌入式超声传播时间测量装置。该装置电路运行稳定,成本低廉,采用多次测量结果取算数平均值的方法以减小随机干扰,采用参比方法放置接收探头以消减电路中电子器件的延时。通过对实验结果进行分析,得出该装置可精准测量超声波在实验试块中的传播时间且满足设计要求,分辨率可达一纳秒。