Frequency-dependent acoustic energy focusing in hexagonal ceramic micro-scaffolds

Acoustic properties of an additive-manufactured SiC scaffold with hexagonal symmetry fabricated by the robocasting method are studied both numerically and experimentally. The numerical analysis is based on the finite element method (FEM) using Bloch boundary conditions. The calculations show both angular and frequency dispersion of the acoustic waves with wavelengths comparable to the spacing between the rods, i.e., on a millimeter scale, indicating interesting acoustic properties in the MHz range. The dispersion character leads to focusing of the energy propagation into the directions of the rods of the hexagonal structure. This is illustrated by modal-based calculations of the propagation of longitudinal and out-of-plane shear wave packets with a dominant wavelength. The experimental analysis consists of two steps, the measurement of the resonant spectrum and shear wave propagation character. The measured resonant spectrum is in good agreement with the one calculated using numerically obtained low-frequency properties of the structure, also showing the quality of the overall manufactured structure. The time-domain measurement shows significant changes in the energy propagation between low and high frequencies, as predicted by FEM calculations.     

基于多通道时间反转Lamb波的铝板小缺陷检测

超声Lamb波具有传播距离远、衰减小等特点,广泛应用于板结构的无损检测。将Lamb波检测技术与时间反转理论相结合,能提高铝板中小缺陷的检测能力。采用多通道时间反转板中Lamb波聚焦方法对1mm厚的铝板中直径0.8mm通孔缺陷进行检测,检测结果显示多通道时间反转检测信号中形成了两处明显的聚焦,即直达波和缺陷回波聚焦,证明此方法有效提高了检测分辨铝板小缺陷的能力。最后通过直达波、缺陷回波两处聚焦的时间差和Lamb波S_0模态群速度,准确实现了铝板中小缺陷的定位。多通道时间反转Lamb波聚焦方法不仅得到了缺陷检测回波,而且准确实现了缺陷的定位,达到了提高铝板中小缺陷检测能力的目的。     

Enhancement of pupil-masked wavelength-scale gas-filled flat acoustic lens based on anomaly apodization effect

In this letter, the improvement in focus by the use of a pupil mask produced in an acoustic mesoscale cuboid particle filled with CO₂ is reported. Thereby, the result shows that the pupil mask increases the sound intensity and also increases the resolution (or a reduction of the full width at half maximum, FWHM) in focus compared to the non-masked one. These results are important because they confirm the effect of abnormal amplitude apodization for a one-wavelength dimension acoustic lens and demonstrate that it is possible to improve sound focusing of a cuboid gas-filled lens with one wavelength dimension. This is the smallest size of an acoustic lens ever considered in this type of literature, with side dimensions of the cube equal to one wavelength and a diameter to focus ratio of 2.5, the sound amplification in focus is 5.4 dB at 4125 Hz, with the resolution near to the diffraction limit.     

非均匀波导中的声聚焦

理论研究了声波在非均匀波导中的空间聚焦问题,利用多模态导纳法构建波导内任意位置处声压与入射声压在模态域的映射关系,计算使声波聚焦于空间某位置时的最佳入射波,并画出了相应的聚焦声场.研究了三种非均匀情况:水平变截面波导、含散射体波导以及声速垂直变化波导.结果表明,当输入最佳入射波时,在非均匀波导中可以产生良好的单点或多点声聚焦效果,声波的聚焦过程充分地利用了波导结构及介质非均匀性对声波的散射作用.     

非齐次动力学方程的一种精细积分单步方法

针对非齐次动力学方程■,结合精细积分法和微分求积法,利用同阶的显式龙格-库塔法对计算过程中待求的v_(k+i/s)(i=1,2,…,s)进行预估,提出了一种避免状态矩阵求逆的高效精细积分单步方法。该方法采用精细积分法计算e~(Ht),而Duhamel积分项采用s级s阶的时域微分求积法,计算格式统一且易于编程,可灵活实现变阶变步长。仿真结果表明,与其他单步法及预估校正-辛时间子域法进行数值比较,该方法具有高精度、高效率及良好的稳定性,在求解大规模动力系统时间响应问题中具有较大的优势。     

Analysis of genetic variants of transferrin in human serum after desialylation by capillary zone electrophoresis and capillary isoelectric focusing

Capillary electrophoresis analysis of transferrin in human serum is used to assess genetic variants after desialylation with neuraminidase and iron saturation to reduce the complexity of the transferrin pattern and thus facilitate the recognition of transferrin polymorphisms. Asialo‐transferrin forms are analyzed by capillary zone electrophoresis using assay conditions as for the monitoring of carbohydrate‐deficient transferrin or by capillary isoelectric focusing in a pH 5–8 gradient which requires immunoextraction of transferrin prior to analysis. With the carrier ampholytes used, peaks for iron saturated and iron depleted transferrin are monitored which indicates complexation of iron ions by carrier ampholytes. For BC, CD, and BD genetic variants, the expected peaks for B, C, and D forms of transferrin were detected with both methods. Monitoring of CC patterns revealed three cases, namely those producing double peaks in both methods, a double peak in capillary isoelectric focusing only and a double peak in capillary zone electrophoresis only. For all samples analyzed, data obtained by capillary isoelectric focusing could be confirmed with gel isoelectric focusing. The two capillary electrophoresis methods are shown to represent effective tools to assess unusual transferrin patterns, including genetic variants with dissimilar abundances of the two forms.     

Advanced online mass spectrometry detection of proteins separated by capillary isoelectric focusing after sequential injection

Capillary isoelectric focusing hyphenated with mass spectrometry detection, following the sequential injection of the carrier ampholytes and the sample zone, is highly efficient for the characterization of proteins. The main advantage of the sequential injection protocol is that ampholytes, with pH ranges, which are not supposed to cover the isoelectric points of the sample components, can be used for separation. The method then allows online mass spectrometry detection of separated analytes either in the absence (substances that have left the pH gradient) or in the presence of low‐level ampholytes (substances that are migrating within the pH gradient). The appearance of the substances within, or outside the pH gradient depends on, e.g., the composition of the ampholytes (broad or narrow pH range) or on the composition of electrolyte solutions. The experiments performed in coated capillaries (with polyvinyl alcohol or with polyacrylamide) show that the amount and the injection length of the ampholytes influence the length of the pH gradient formed in the capillary.     

α-混合序列部分和乘积精确渐近性的一般形式

利用前人获得的α-混合序列部分和乘积的渐近分布的结果,对一般的边界函数和拟权函数得到了α-混合序列部分和乘积的精确渐近性的一般形式.     

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In this paper, by using central limit theorem of ND sequences and probability inequality, the precise asymptotics for partial sums of nonstationary ND sequences is investigated, and the same results with it under that of NA sequences are obtained.     

Ion transmission in an electrospray ionization-mass spectrometry interface using an S-lens

We present the design and performance of an in-house built electrospray ionization-mass spectrometry (ESI-MS) interface equipped with an S-lens ion guide. The ion source was designed specifically for our ion beam experiments to investigate the chemical reactivity and deposition of the clusters and nanoparticles. It includes standard ESI-MS interface components, such as nanoelectrospray, ion transfer capillary, and the S-lens. A custom design enables systematic optimization of all relevant factors influencing ion formation and transfer through the interface. By varying the ESI voltage and flow rate, we determined the optimal operating conditions for selected silica emitters. A comparison of the pulled silica emitters with different tip inner diameters reveals that the total ion current is highest for the largest tip, whereas a tip with the smallest diameter exhibited the highest transmission efficiency through the ESI-MS interface. Ion transmission through the transfer capillary is strongly limited by its length, but the loss of ions can be reduced by increasing the capillary voltage and temperature. The S-lens was characterized over a wide range of RF frequencies and amplitudes. Maximum ion current was detected at RF amplitudes greater than 50 V peak-to-peak (p/p) and frequencies above 750 kHz, with a stable ion transmission region of about 20%. A factor of 2.6 increase in total ion current is observed for 650 kHz as RF amplitudes reach 400 V p/p. Higher RF amplitudes also focus the ions into a narrow beam, which mitigates their losses when passing through the ion guide.