Vibration of a single microcapsule with a hard plastic shell in an acoustic standing wave field

Observation techniques for measuring the small vibration of a single microcapsule of tens of nanometers in an acoustic standing wave field are discussed. First, simultaneous optical observation of a microbubble vibration by two methods is investigated, using a high-speed video camera, which permits two-dimensional observation of the bubble vibration, and a laser Doppler vibrometer (LDV), which can observe small bubble vibration amplitudes at high frequency. Bubbles of tens of micrometers size were trapped at the antinode of an acoustic standing wave generated in an observational cell. Bubble vibration at 27 kHz could be observed and the experimental results for the two methods showed good agreement. The radial vibration of microcapsules with a hard plastic shell was observed using the LDV and the measurement of the capsule vibration with radial oscillation amplitude of tens of nanometers was successful. The acoustic radiation force acting on microcapsules in the acoustic standing wave was measured from the trapped position of the standing wave and the radial oscillation amplitude of the capsules was estimated from the theoretical equation of the acoustic radiation force, giving results in good agreement with the LDV measurements. The radial oscillation amplitude of a capsule was found to be proportional to the amplitude of the driving sound pressure. A larger expansion ratio was observed for capsules closer to the resonance condition under the same driving sound pressure and frequency.     

Stochastic plastic analysis of a shell

A method is proposed for the inclusion of stochastic parameters, using a Monte Carlo simulation technique, in the lower bound plastic analysis of a structural continuum by non-linear mathematical programming. The particular example chosen is a circular, cylindrical concrete silo subject to loading by its contents.     

球形壳体障板声散射近场矢量特性

为了实现矢量水听器在水面或水下载体上的工程应用,研究了球形壳体障板声散射近场矢量特性。采用弹性薄壳理论结合边界条件导出了球形壳体障板声散射的声压和质点振速表达式,给出相应的声强表达式。数值计算了球形壳体障板声散射的近场特性,重点关注其近场矢量特性。理论分析和数值计算结果表明,由于球形壳体障板的散射作用,声压场和质点振速场表现为复杂的干涉结构;质点振速方向和声源方位不一致;声压和质点振速不再同相;声强方向也不再反映声源方位。本文结果为矢量水听器在球形载体和球形障板条件下的工程应用提供理论依据。     

Influence of lipid shell physicochemical properties on ultrasound-induced microbubble destruction

We present the first study of the effects of monolayer shell physicochemical properties on the destruction of lipid-coated microbubbles during insonification with single, one-cycle pulses at 2.25 MHz and low-duty cycles. Shell cohesiveness was changed by varying phospholipid and emulsifier composition, and shell microstructure was controlled by postproduction processing. Individual microbubbles with initial resting diameters between 1 and 10 microm were isolated and recorded during pulsing with bright-field and fluorescence video microscopy. Microbubble destruction occurred through two modes: acoustic dissolution at 400 and 600 kPa and fragmentation at 800 kPa peak negative pressure. Lipid composition significantly impacted the acoustic dissolution rate, fragmentation propensity, and mechanism of excess lipid shedding. Less cohesive shells resulted in micron-scale or smaller particles of excess lipid material that shed either spontaneously or on the next pulse. Conversely, more cohesive shells resulted in the buildup of shell-associated lipid strands and globular aggregates of several microns in size; the latter showed a significant increase in total shell surface area and lability. Lipid-coated microbubbles were observed to reach a stable size over many pulses at intermediate acoustic pressures. Observations of shell microstructure between pulses allowed interpretation of the state of the shell during oscillation. We briefly discuss the implications of these results for therapeutic and diagnostic applications involving lipid-coated microbubbles as ultrasound contrast agents and drug/gene delivery vehicles.     

Recycling of a plastic car component having a multilayer structure: Morphological and mechanical analysis

The recycling of two types of dashboards having a multilayer structure presently available on the market and hence on the scrap cars has been extensively investigated. In both the cases the recycled material showed a strong worsening in the mechanical and impact properties. This effect was attributed to the incompatibility of the different materials constituting the item and to the occurrence of degradation phenomena taking place during processing. To overcome these limitations suitable polymeric additives were added during the recycling. By this procedure materials with improved mechanical properties able to be reused for the same or for similar applications within the car have been obtained.     

带球壳微泡和空化气泡的超声特性研究

在临床应用中,微泡在低频超声作用下能比较成功地导致微血管的栓塞,从而切断对肿瘤的供血来达到杀灭肿瘤的目的,而通过实验的手段来获得其微泡的超声散射特性十分困难。根据经典的微泡模型,应用范德瓦耳斯绝热方程来进行修正,分别对带球壳微泡和空化气泡建立模型,模拟其运动过程,并对两种微泡的散射特性进行了分析与比较,研究了不同驱动声场的频率和微泡初始平衡半径对微泡运动的影响。结果表明,带球壳微泡在微泡初始平衡半径大于2.2μm时较空化气泡有较好的散射特性,其最大散射压力和散射截面随着频率的增大而减小,带球壳微泡在散射特性方面的优势使其能更有效地进行超声治疗和成像,为超声造影剂等微泡的研究和应用提供了理论指导。     

带缺口塑性材料的声发射特性研究

以带线切割加工缺口的碳钢在拉伸试验时的断裂过程为研究对象,通过对其产生的声发射信号进行检测和分析,研究其开裂时的声发射特性。试验结果表明:带缺口塑性材料在拉伸断裂过程中会产生幅值在47dB￣90dB范围内的声发射信号;信号的振铃累计数在材料的塑性变形段与裂纹稳态扩展段均与应变成线性关系,但后者斜率大于前者;试样缺口深度越大,材料开裂时间越早,振铃计数率越高,且信号能量累计数与应变成线性关系。     

有阻尼负载时圆柱壳的声传递特性分析

摘要 本文分析研究有阻尼负载圆柱壳的声波透射问题,从经典薄壳理论出发,给出有阻尼负载的圆柱壳振动微分方程,结合均匀流场中的波动方程,利用流-固耦合边界条件,给出了声波传递损失的公式,并计算了相应的算例,研究了有阻尼负载圆柱壳中的声波传递特性。分析了声波入射角度、阻尼厚度、壳体厚度等对声波传递损失的影响,得到了有意义的结论,旨在为工程设计提供参考。     

Application of the complete thermochemical model of carbon destruction to the problem of destruction of carbon-fiber reinforced plastic material under transient heating

A solution of the problem of transient heating and destruction of a carbon-fiber reinforced plastic (CFRP) material is presented, which was obtained using the complete thermochemical model of carbon ablation. The results of calculations are compared with the corresponding data for pure carbon material.     

The in vitro dissolution of theophylline from different types of hard shell capsules

The in vitro dissolution of theophylline from two-piece hard shell capsules has been investigated using different types of capsule shells (gelatin, gelatin/polyethylene glycol, hydroxypropyl methylcellulose), different formulations, different capsule fill weights, and different tamping forces. Analysis of variance confirmed that the formulation and the capsule shell materials were the most important factors influencing drug dissolution. The maximum extent of drug dissolution was significantly increased when hydroxypropyl methylcellulose (HPMC) capsules were used. The mean dissolution time (MDT) was significantly reduced, indicating a faster dissolution rate of the drug from HPMC capsules. The addition of microfine cellulose to the formulations as filler reduced the MDT in all cases, whereas the addition of lactose monohydrate did not enhance drug dissolution. The study confirmed that a change from gelatin hard shell capsules to gelatin/PEG or HPMC hard shell capsules should not pose problems with respect to drug absorption or bioavailability.     

Non-linear programming for the plastic analysis of local deformations in shell structures

The paper presents an analysis of the response of plastic spherical and cylindrical shells subjected to loads applied through a rigid boss. Special emphasis is placed on following the load-deflection behaviour of these structures after the application of the yield-point load in order to predict the appearance of any snapping action. The method of analysis assumes that upper bound calculations are applicable and that the associated velocity fields can be represented by a series of piecewise continuous polynomials. The internal dissipation of energy for the structures are then written in terms of the coefficients of these polynomials and the values appropriate to the solution are found by using a non-linear programming routine. The results of this analysis are correlated with a non-dimensional boss size parameter p and compared with the results of experimental investigations. Mention is also made of the possible effects of initial imperfections.     

海藻酸钙-聚精氨酸聚电解质微胶囊强度性能研究

制备了一种新型的聚精氨酸基微胶囊并考察了制备条件对微胶囊机械强度性能的影响,以期望制备一种具有介入治疗效果的药物载体.实验采用高压静电液滴发生装置,所制备的微胶囊粒度均匀、球形度好.同时,海藻酸钠浓度、成膜时间以及聚精氨酸分子量对微囊膜的机械强度有不同程度的影响.当海藻酸钠浓度为1.0%,成膜时间高于15min,聚精氨酸分子量为55,300和141,000μ时,膜机械强度最好.此外,实验初步考察了聚电解质络合反应机理.结果表明,通过改变实验条件,可有效地控制微囊膜的膜强度,从而为进一步的药物控制释放实验打下一定的基础.     

Discrimination of the hard keratins animal horn and chelonian shell using attenuated total reflection-infrared spectroscopy

The ability to discriminate between objects manufactured from animal horn and chelonian (turtle, tortoise, or terrapin) shell is important from a cultural and archeological perspective such that it may allow conservators to determine the appropriate treatment and long-term care solution. It would also aid curators in identifying and cataloging items manufactured from these materials. Discrimination and classification is also a valuable tool for those involved in tracking the illegal trade in restricted materials of this nature. Attenuated total reflection infrared (ATR-IR) spectroscopy, using a single reflection diamond internal reflection element (IRE), coupled with discrimination analysis was used to analyze a total of thirty-nine samples (29 calibration samples, 10 validation samples). A discrimination analysis model was constructed using Mahalanobis distances to classify spectra into one of two classes. The model was then subsequently used to successfully classify all validation samples and correctly identify them as animal horn or chelonian shell based on second-derivative spectra of the amide I and II regions. This technique requires minimal to no sample preparation and may be used to nondestructively identify very small samples successfully without performing detailed secondary structural curve-fitting routines. This model should be a valuable resource to museums, conservators, and wildlife management programs for rapidly and reliably discriminating between animal horn and chelonian shell.