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1.
A novel method for mapping inertial cavitation activity during high-intensity focused ultrasound (HIFU) exposure is presented. Inertial cavitation has been previously shown to result in increased heat deposition and to be associated with broadband noise emissions that can be readily monitored using a passive receiver without interference from the main HIFU signal. In the present study, the signals received passively by each of 64 elements on a standard diagnostic array placed coaxially with the HIFU transducer are combined using time exposure acoustics to generate maps of inertially cavitating regions during HIFU exposure of an agar-based tissue-mimicking material. The technique is shown to be effective in localizing single-bubble activity, as well as contiguous and disjoint cavitating regions instigated by creating regions of lower cavitation threshold within the tissue phantom. The cavitation maps obtained experimentally are also found to be in good agreement with computational simulations and theoretical predictions. Unlike B-mode imaging, which requires interleaving with the HIFU pulse, passive array-based mapping of cavitation activity is possible during HIFU exposure. If cavitating regions can be directly correlated to increased tissue damage, this novel cavitation mapping technique could enable real-time HIFU treatment monitoring.   相似文献   
2.
Targeted vascular occlusion is desirable for clinical therapies such as in the treatment of esophageal and gastric varices and varicose veins. The feasibility of ultrasound-mediated endothelial damage for vascular occlusion was studied. A segment of a rabbit auricular vein was treated in vivo with low duty cycle, high peak rarefaction pressure (9 MPa) high-intensity focused ultrasound pulses in the presence of intravenously administered circulating microbubbles, followed by fibrinogen injection, which resulted in the formation of an acute occlusive intravascular thrombus. Further investigation and refinements of treatment protocols are necessary for producing durable vascular occlusion.   相似文献   
3.
阐述了目前斜井人车缓冲装置的缓冲原理和存在的问题,提出了一种缓冲可靠、造价低廉、调力方便的摩擦片式缓冲装置,并利用优化设计的方法进行了机构的设计。  相似文献   
4.
根据生产实践数据,对转炉炉役的经济性进行了动态分析。  相似文献   
5.
高性能各向异性Sm2Fe17Nx磁粉的制备   总被引:5,自引:0,他引:5  
李佛标  于申军 《功能材料》1996,27(6):498-501
本文研究了高性能各向异性Sm2Fe17Nx磁粉的制备工艺路线与工艺参数。优化了制备与工艺参数。已制备出磁性能达到:Br=1.39T,Hci=850KA/m和(BH)m=236KJ/m^3的各向异性Sm2Fe17N2.88磁粉,该磁粉的各向异性场HA达到20T。  相似文献   
6.
断裂顶板锚拉支架支护系统的分叉行为   总被引:1,自引:0,他引:1  
侯公羽  李先炜 《煤炭学报》1996,21(6):586-590
应用弹性系统稳定性理论对断裂顶板-锚拉支架系统建立了动力系统稳定性分析的力学模型.对该模型分别考虑因块AB(或BC)沿对角线变形和支座处的水平变形引起的稳定性进行了求解;讨论了解曲线即平衡路径的稳定性及系统的静态分叉特征;进而分析了断裂顶板结构的运动失稳机制,并给出了该系统的运动稳定条件,证实了借助当代非线性科学研究岩土工程问题的必要性和理论意义.  相似文献   
7.
苯和二异丙苯烷基转移化反应的研究   总被引:2,自引:0,他引:2  
研究了二异丙苯转移烷基化反应中,催化剂配制条件等因素对反应的影响,对均相条件下的二异丙苯转移烷基化反应动力学进行了研究,得到了反应动力学方程。  相似文献   
8.
Magnesium alloys based on Nd and Zn are promising materials for both aviation industry and medical applications.Superior mechanical properties of these materials can be achieved by thermomechanical processing such as extrusion or rolling and by aging treatment, which can significantly strengthen the alloy. The question remains especially about the connection of texture strength created in the alloys based on the specific conditions of preparation. This work focuses on the Mg–3 Nd–0.5 Zn magnesium alloy prepared by hot extrusion of the as-cast state at two different temperatures combined with heat pre-treatment. Extrusion ratio of 16 and rate of 0.2 mm/s at 350 and 400 °C were selected for material preparation. The structures of prepared materials were studied by scanning electron microscopy and transmission electron microscopy. The effect of microstructure on mechanical properties was evaluated. Obtained results revealed the strong effect of thermal pre-treatment on final microstructure and mechanical properties of extruded materials. The Hall–Petch relation between grain size and tensile yield strength has been suggested in this paper based on the literature review and presented data. The observed behavior strongly supports the fact that the Hall–Petch of extruded Mg–3Nd–0.5 Zn alloys with different texture intensities cannot be clearly estimated and predicted. In addition, Hall–Petch relations presented in literature can be sufficiently obtained only for fraction of the Mg–3Nd–0.5 Zn alloys.  相似文献   
9.
本文介绍了双阀值窗口比较开关及三态比较开关的基本工作原理及应用。  相似文献   
10.
吴德龙 《炼钢》1996,12(6):60-63,34
简述了当前电力不足,电弧炉炼钢采用超高功率的技术的迫切需要,分析了超高功率技术的主要特点,对我国发展超高功率技术的难点提出了已见。  相似文献   
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