刚性壁面附近多空化泡辐射噪声的研究

对空化泡在刚性壁面附近溃灭过程中的辐射声场进行研究,并得出刚性壁面附近单空泡、双空泡的辐射声压分布。研究表明由于刚性壁面的影响使得空化泡的辐射声场表现出一定的指向性。双空泡辐射声压分布还与空泡崩溃时间、空泡之间距离以及空化泡初始半径有关。在考虑到声压相位叠加时,待测点处的辐射声压依赖于空泡的声压幅值[p]和两空泡到观察点的声程差[Δ1=l12sinθ1]和[Δ2=l22sinθ2]。计算过程及结果为刚性壁面附近的空化计算提供依据,并为多泡空化的辐射声场分析提供理论依据,有助于修正空化泡的运动方程。     

人组织液医学超声空化阈值的研究

本文用荧光法检测医用理疗级连续波超声作用于人组织液（血清，血浆）发生空化产生的自由基，超声阈值强度ＩＳＡＴＡ（空间平均时间平均声强）分别为０．７５Ｗ／ｃｍ＾２～０．８５Ｗ／ｃｍ＾２和０．７Ｗ／ｃｍ＾２。本研究证明荧光法是检测医学超声空化的有效方法，并提供离体人组织液超声空化安全阈值的研究结果，同时发现人血清，人血浆空化的程度工化与声强相关关系不同。     

GTAW焊接过程声音信号的分析

研究分析钨极氩弧焊（GTAW）时焊接气流,焊接速度,电弧长度和声音信号采集角度对采集到的声压信号的影响。结果表明：速度对声压影响最小;焊接声音随气体流增加而增加,当流量大于15L／min,声压信号趋于恒定;电弧长度在3．5—5mm之间时,声压随弧长变化显著,当超过5mm时变化不明显;声压随麦克风采集角的增加而增加,当大于60°时声压值变化不大,焊接声压强度在空间的分布近似于声源模型中的偶极子模型。     

磁致伸缩仪超声空化流的数值研究

基于CFD方法采用"Singhal完全空化模型"及动网格技术对磁致伸缩仪超声空化流进行数值计算。结果表明,变幅杆高频振动引起试样表面附近局部流场发生空化,且在试样表面形成脉冲压力;压力与空泡体积组分在试样表面近似呈环形分布,并随试样振动,二者周期性变化。试样表面中心区域空泡经两次振荡后溃灭产生强烈脉冲压力,峰值可达5 MPa;脉冲压力在试样表面按间隔环形区域分布,且随试样振动在相邻环形区域交替出现。随超声波在空化流场中传播声压快速衰减;压力只在距变幅杆端面约20 mm内波动明显,振幅从25μm增大到30μm时试件中心区域脉冲压力增大;振幅增大到35μm时空化效果增强,试件中心区域所受脉冲压力作用减弱。     

冷侧真空度对压膜蒸馏过程影响的研究

和ＰＴＦＥ膜实验研究了冷侧真空度地减压膜蒸馏过程的影响，实验结果表明，随冷侧真空度的提高，蒸汽的渗透能量增加，分离率也增加，渗透能量和两侧的蒸汽压差成正比，若真空度很高，且冷侧的绝压比膜冷侧的饱和蒸汽压低时，渗透通量有剧增的趋势；渗透能量和膜的孔径大小有关，孔径越大，通量越大。     

磁性聚膦腈纳米管对亚甲基兰的吸附性能研究

采用原位模板法在室温下合成了贯穿型磁性聚膦腈纳米管,研究了该磁性聚膦腈纳米管对有机染料亚甲基兰的吸附作用。分别讨论了吸附时间、吸附温度、亚甲基兰的初始浓度及磁性聚膦腈纳米管用量对吸附性能的影响。结果表明,合成的含11.5%Fe3O4的贯穿型磁性聚膦腈纳米管的比磁饱和强度Ms为2.68A.m2/kg,磁响应性强烈,分散在水中后可通过钕铁硼永久磁铁迅速富集;吸附率随吸附时间的延长逐渐增大,72h时几乎可吸附完全;吸附行为较好地符合Langmuir模型;吸附率随亚甲基兰初始浓度的增加而减小,随磁性聚膦腈纳米管用量的增加而增加;吸附率和吸附量随温度的升高而增大,在60℃时,几乎吸附完全。     

超声空化效应对溶液电导率的影响

大功率超声作用于溶液时会产生空化效应,并影响溶液的物理化学性质,如电导率、液体粘度及液体表面张力等。文章对不同功率的超声作用于弱电解质溶液时其电导率的变化进行了实验研究,发现溶液电导率与超声波强度有关。当强度增大到有空化产生时,电导率开始减小;继续增大强度,溶液电导率减小到一定程度后有小幅回升现象出现。且液体内空化效应的出现将导致液体的电导率减小,空化达到一定强度时,空化效应引起的局部瞬态高温高压、冲击波和微射流导致的新导电粒子,会使电导率小幅回升。     

超声辅助电火花放电制备微纳米镍颗粒中超声功率对颗粒粒径的影响

超声辅助电火花放电是一种绿色环保、易于控制的制备微纳米金属粉末的方法.为研究超声功率对微纳米金属粉末粒径分布的影响,本工作通过COMSOL仿真软件模拟声压在工作液中随时间的变化趋势,得出不同换能器功率下工作液中的最大声压值.利用测量得到的最大声压值与工作液理论空化阈值的比较确定了换能器的功率值,通过理论计算得到了不同超声功率对粒径的影响范围.最后采用实验室自制设备制备镍粉,通过SEM观测制备的镍粉的形貌,采用激光粒度分析仪分析镍粉的粒径分布,验证了理论分析结果.结果表明:超声的空化与振动效应能够破碎火花放电产生的汽化和熔融金属液滴;工作液中的空化泡破裂所产生的冲击波使小粒径的镍粉颗粒发生碰撞,动能转换成热能,产生的高温使镍颗粒烧结形成金属烧结颈,使多个小颗粒团聚成不规则的大颗粒.     

低温流体经过弯管时的空化现象分析

采用完全空化模型,对液氧流经弯管中时的空化现象进行了数值模拟.研究表明:由于弯管内侧流体压力低于外侧,当最低压力降低到空化核不稳定的临界压力时,空化首先在弯管内侧产生;入口速度增加、出口压力降低或流体温度升高,均会导致空化区域增大、强度增加.当空化区域扩展到一定范围时,管内大部分区域的流动状态达到基本稳定,空化现象对入口速度、出口压力等操作参数的变化不再敏感.此外,弯管的几何结构如曲率变化对空化现象也有相当大的影响.     

柱形料腔中超声空化效应的空间分布特性研究

研究了20 kHz的圆柱形料腔中超声空化效应的形成及其空间分布特性。应用柱贝塞尔函数,推导获取了柱形声场内超声传播的声能密度的分布,并采用有限元方法进行仿真分析。针对频率为20 kHz的功率超声实验,结合声学测量方法和鲁米诺声致化学发光方法,对理论分析结果进行了验证对照。结果表明:料腔半径R=50 mm,20 kHz谐振液位高度H=90 mm时,若功放电流<40 mA,超声空化效应出现在变幅杆端部区域;若40 mA≤功放电流≤80 mA,空化效应显著增强,空化效应的空间分布与场内声压分布一致,空化效应受声模态影响,形成远场空化效应的分布特性;若功放电流>80 mA,受非线性因素影响,谐振液位时,空化效应在声流作用下呈柱形拖尾状分布,并在底部壁面边界形成平铺状分布;非谐振液位高度等于75 mm时,超声空化效应随功率增加仅在变幅杆端部区域出现,且呈现局域空化分布特性。     

Thresholds for inertial cavitation in albunex suspensions under pulsed ultrasound conditions

Stabilized microbubbles used as echo-contrast agents can be destroyed by ultrasonic irradiation. We have identified two pressure thresholds at which these microbubbles undergo inertial cavitation (here, defined as the collapse of gas bubbles followed by emission of an acoustic broadband noise). The first threshold (P1) corresponds to the pressure at which all the microbubbles in a cavitation field lose their property as an effective scatterer because of fragmentation or deflation. The second threshold (P2) is associated with the acoustic reactivation of the remnants of the contrast agents and is related to the onset of more violent inertial cavitation. P1 and P2 were measured as a function of the concentration of Albunex(R) (Molecular Biosystems Inc., San Diego, CA) contrast agent, the number of transmitting acoustic cycles, and the pulse repetition frequency (PRF). The ultrasound frequency used was 1.1 MHz, and the peak negative acoustic pressures ranged from 0 to 8 MPa. Our results, measured in Isoton(R) II (Coulter Diagnostics, Miami, FL) and whole blood solutions, showed that P1 increased with increasing Albunex(R) concentration and decreased with increasing PRF, whereas P2 decreased with increasing Albunex(R) concentration and was independent of the PRF. Both P1 and P2 decreased with increasing number of acoustic cycles N for N<10 and were independent of the number of cycles for N>10. Ultrasound images of Albunex(R) acquired by a commercial scanner showed echo enhancement not only at pressure levels below P1 but also at levels above P2. The threshold P2 was achieved at ultrasound energies above the diagnostic level. Inertial cavitation produced at P2 was associated with a higher level of hemolysis compared with P1. The results of this investigation have potential significance for both diagnostic and therapeutic ultrasound applications     

Influence of unsaturated carbonic acids on hemocompatibility and cytotoxicity of poly-vinylacetate based co-polymers

The aim of this study was to investigate hemocompatibility and cytotoxicity properties of synthetic polymer coatings containing various unsaturated carbonic acids with vinylacetate. Co-polymers of vinylacetate and crotonic acid (CA), maleic acid (MA), and itaconic acid (IA) were made. The materials were characterized in terms of their adhesion to metal supports (titanium and stainless steel) as well as hemocompatibility (% hemolysis, wettability, erythrocyte aggregation, hemoglobin content, thrombocyte count and lipid peroxidation levels) and cytotoxicity (human endothelial cell activity in vitro and chromosome aberrations, bone marrow proliferation and cell ploidy in rats). Co-polymers of unsaturated carbonic acids with vinylacetate exhibited good hemocompatibility properties, as opposed to vinylacetate homopolymer for which substantial levels of hemolysis were observed. By coating the metal supports with co-polymers the cytotoxic effects associated with the bare metal samples were markedly reduced. MA samples showed excellent hemocompatibility and no cytotoxicity, yet they lacked good adhesion properties to metal substrate, probably due to high water content. CA samples, having the highest density of carboxylic groups among the samples under investigation, showed increased bone marrow proliferation activity and cell ploidy in rats, as compared to controls. The most promising results in the present study were obtained for the samples with IA, which showed good adhesion to metal substrates, good hemocompatibility and low cytotoxicity. Thus, co-polymers of vinylacetate and IA rich in carboxylic groups are promising materials for the design of novel drug-eluting stents.     

Relationship between the cavitation threshold and maximum sonoluminescence intensity

A phenomenological rule establishing a relationship between the cavitation threshold and the maximum intensity of sonoluminescence (SL) induced by ultrasound is formulated on the basis of experimental data for various liquid media. According to this, the maximum SL intensity attained by varying the intensity of ultrasound within broad limits is always greater in a medium characterized by a higher cavitation threshold.     

A real-time controller for sustaining thermally relevant acoustic cavitation during ultrasound therapy

A novel method for sustaining inertial cavitation during high-intensity focused ultrasound (HIFU) exposure in an agar-based tissue-mimicking material is presented. Inertial cavitation occurs during HIFU therapy when the local rarefaction pressure exceeds the inertial cavitation threshold of the insonated medium, and is characterized by broadband acoustic emissions which can be easily detected non-invasively using a passive cavitation detector (PCD). Under the right conditions, inertial cavitation has been previously shown to greatly enhance the rate of heat deposition by redistributing part of the energy carried at the fundamental HIFU frequency to higher frequencies, which are more readily absorbed by visco-elastic media such as soft tissue. However, in the absence of any cavitation control, inertial cavitation activity at the focus decays rapidly over a few seconds of exposure because of the combined effects of cavitation nuclei depletion, bubble dissolution, bubble-bubble interactions, increased vapor pressure caused by heating, and focal shielding caused by pre-focal bubble activity. The present work describes the design, validation, and testing of a real-time adaptive controller, with integrated passive localization capabilities, for sustaining inertial cavitation within the focal region of a HIFU transducer by modulation of the HIFU amplitude. Use of the controller in agar gel, originally at room temperature, has enabled therapeutically relevant temperatures in excess of 55°C to be maintained continuously in the focal region for more than 20 s using significantly less acoustic energy than is required to achieve the same temperature rise in the absence of cavitation control.     

Ultrasound‐Propelled Nanocups for Drug Delivery

Ultrasound‐induced bubble activity (cavitation) has been recently shown to actively transport and improve the distribution of therapeutic agents in tumors. However, existing cavitation‐promoting agents are micron‐sized and cannot sustain cavitation activity over prolonged time periods because they are rapidly destroyed upon ultrasound exposure. A novel ultrasound‐responsive single‐cavity polymeric nanoparticle (nanocup) capable of trapping and stabilizing gas against dissolution in the bloodstream is reported. Upon ultrasound exposure at frequencies and intensities achievable with existing diagnostic and therapeutic systems, nanocups initiate and sustain readily detectable cavitation activity for at least four times longer than existing microbubble constructs in an in vivo tumor model. As a proof‐of‐concept of their ability to enhance the delivery of unmodified therapeutics, intravenously injected nanocups are also found to improve the distribution of a freely circulating IgG mouse antibody when the tumor is exposed to ultrasound. Quantification of the delivery distance and concentration of both the nanocups and coadministered model therapeutic in an in vitro flow phantom shows that the ultrasound‐propelled nanocups travel further than the model therapeutic, which is itself delivered to hundreds of microns from the vessel wall. Thus nanocups offer considerable potential for enhanced drug delivery and treatment monitoring in oncological and other biomedical applications.     

Optimizing hemocompatibility of surfactant-coated silver nanoparticles in human erythrocytes

Several recent biological science studies have been focused on nanotechnology and nanomaterials due to their potential use in biomedicine. Drug delivery systems are an example of biomedical applications utilizing nanoparticles. Silver nanoparticles (AgNPs) can be used for these drug delivery systems. However, the effects of cytotoxicity caused by AgNPs are not fully understood. Determining the optimal characteristics to facilitate the biocompatibility of AgNPs is an important subject for application. In the present study, human erythrocytes were used as an in vitro model to examine the size, dose, and coating surfactant-dependent cytotoxicity of AgNPs. Our results demonstrated that polyvinylpyrrolidone (PVP) was a more suitable surfactant than polyethylene glycol (PEG) for AgNPs capping. In addition, we determined the appropriate particular size and dosage of AgNPs to reduce human erythrocytes hemolysis. Membrane damages including hemolysis, potassium efflux, protein leakage, and alterations in cell shape and membrane fragility were minimized with 100-nm AgNP particles. This study provides novel insights into AgNPs cytotoxicity and a basis for utilizing AgNPs for diagnostic and therapeutic applications.     

Cytocompatibility and Hemolysis of AZ31B Magnesium Alloy with Si-containing Coating

In the present study,a Si-containing coating was fabricated on AZ31 B Mg alloy.Cytocompatibility of the coated alloy was evaluated by both indirect and direct contact methods,respectively.Effects of a number of incubation variables on the sensitivity and reproducibility of the hemolysis test were also examined by using positively and negatively responding biomaterials.Cytocompatibility testing results indicated that cell condition,cell adherence,cell proliferation and extracellular matrix secretion of the coated alloy were improved compared with those of the uncoated alloy for different extraction and co-culture time.The hemolysis test suggested that hemolysis testing conditions were critical to determine the hemolysis of the alloy.It was also found that 1 day in vitro degradation of the uncoated AZ31 B alloy had no destructive effect on erythrocyte.As for the coated AZ31 B alloy at any time point,the hemolysis rate was much lower than 5%,the safe value for biomaterials.These in vitro experimental results indicate that the Si-containing coating is effective to improve the cytocompatibility and hemolysis behaviors of AZ31 B alloy during its degradation.     

Cavitation in Normal Liquid Helium 3

We have studied cavitation, i.e. bubble nucleation, by focusing ultrasound hurts in normal liquid helium 3 at temperatures down to 40 mK. As in helium 4, cavitation is found to be stochastic, with a cavitation probability 0.5 at a given value of the sound amplitude, which we define as a cavitation threshold. This threshold is found significantly lower in helium 3 than in helium 4, a result which agrees with theoretical predictions of a spinodal limit at - 3.1 bar in helium 3 instead of- 9.5 bar in helium 4- We also measured the temperature variation of this cavitation threshold; it decreases with temperature as expected for a thermally activated nucleation process. We have not yet found any evidence for a crossover toward cavitation by quantum tunneling below 120 mK as predicted by several authors; if confirmed, it might indicate that the superfluid coherence plays a role in quantum cavitation.     

Reversal effect of low‐intensity ultrasound on adriamycin‐resistant human hepatoma cells in vitro and in vivo

The aim of this study was to determine whether the ultrasound, with a dosage that did not lead to acute and delayed inhibition, could potentiate the cytotoxicity of adriamycin to human hepatoma resistant cell line HepG2 both in vitro and in vivo. In order to determine whether low‐intensity ultrasound could reverse resistance in adriamycin‐resistant human hepatoma cell line HepG2/ADM in vitro, cells were subjected to a variable level of ultrasound. The results showed that survival rates were decreased in groups in which ultrasound and adriamycin were exerted. The same effect of low‐intensity ultrasound was also observed in the xenograft tumor experiment. Furthermore, transmission electron microscope revealed the cavitation effects play the determining role in accelerating transmembrane transportation, suggesting that low‐intensity ultrasound altered the cell membrane thus resulting in change in adriamycin uptake into HepG2/ADM cells. Further investigation of the underlying mechanisms showed that the reversal effect of low‐intensity ultrasound on adriamycin‐resistant human hepatoma cells was attributed to the downregulation of the multidrug resistant genes, MDR1 and MRP1, in both mRNA and protein expression. In addition, downregulation of MDR1 and MRP1 was detected in HepG2/ADM xenograft tumor treated with adriamycin and ultrasound. These observations suggest the use of ultrasound could increase cytotoxicity attributable to adriamycin in chemoresistant human hepatoma cancer cells. Ultrasound is a promising therapeutic modality for refractory hepatoma patients.     

Microbubble-enhanced cavitation for noninvasive ultrasound surgery

Experiments were conducted to explore the potential of stabilized microbubbles for aiding tissue ablation during ultrasound therapy. Surgically exteriorized canine kidneys were irradiated in situ using single exposures of focused ultrasound. In each experiment, tip to eight separate exposures were placed in the left kidney. The right kidney was then similarly exposed, but while an ultrasound contrast agent was continually infused. Kidneys were sectioned and examined for gross observable tissue damage. Tissue damage was produced more frequently, by lower intensity and shorter duration exposures, in kidneys irradiated with the contrast agent present. Using 250-ms exposures, the minimum intensity that produced damage was lower in kidneys with microbubbles than those without (controls) in 10 of 11 (91%) animals. In a separate study using /spl sim/3200 W/cm/sup 2/ exposures, the minimum duration that produced damage was shorter after microbubbles were introduced in 11 of 12 (92%) animals. With microbubbles, gross observable tissue damage was produced with exposure intensity /spl ges//spl sim/800 W/cm/sup 2/ and exposure duration /spl ges/10 /spl mu/s. The overall intensity and duration tissue damage thresholds were reduced by /spl sim/2/spl times/ and /spl sim/100/spl times/, respectively. Results indicate that acoustic cavitation is a primary damage mechanism. Lowering in vivo tissue damage thresholds with stabilized microbubbles acting as cavitation nuclei may make acoustic cavitation a more predictable, and thus practical, mechanism for noninvasive ultrasound surgery.