共查询到20条相似文献,搜索用时 15 毫秒
1.
本文介绍了利用超声振动能量制取超细金属粉末的超声雾化方法,提出了超声制粉雾化室,等离子枪,阴极、阳极喷咀及换能器振动系统的最佳尺寸和工作参数,给出了实验结果及制得的粉末显微结构照片.实验结果表明,用本文所述方法制得的金属粉末组成为:-80目粉占84呢,-120目粉占63.7啪,而用PREP方法制得的粉末分别占19.5%和11.7%,由此看来,用本方法制取超细金属粉,在粒度组成方面优于PREP方法.文中还对粉末冷却速度做了估算,得到了粉末平均冷却速度大于1×10_5k/5 相似文献
2.
Ultrasonic phased array controller for hyperthermia applications 总被引:1,自引:0,他引:1
Multiple and mechanically scanned ultrasound transducer systems have demonstrated the efficacy of using ultrasound to produce deep localized hyperthermia. The use of ultrasonic phased arrays has been proposed as an alternative to these systems. A phased array offers a more flexible approach to heating tumours in that the size, shape, and position of its focal region can be altered during the course of treatment in order to achieve the desired temperature distribution. This added flexibility comes at the cost of increased complexity of the hardware necessary to drive the transducer because each element requires its own amplifer with both phase and amplitude control. In order for phased arrays with large numbers of elements to be feasible for hyperthermia applications, the complexity of this circuitry must be minimized. This paper describes a circuit design which simplifies the electronics required to control a phased array transducer system for hyperthermia applications. The design is capable of controlling virtually any type of phased array transducer operating at frequencies less than 2 MHz. The system performance was verified through beam profile measurements using a 48-element tapered phased array transducer. 相似文献
3.
This paper describes the performance and simulation of a compact integrated optical processor for the real-time reconstruction of two-dimensional images in airborne stripmap synthetic aperture radar applications. The functional behavior of the processor is explained in some detail. The design criteria are briefly given. The simulation step allowed the main processor characteristics and properties to be identified. A number of comparisons were obtained in airborne SAR mission scenarios between the predictions of the optical device and those achieved by the modern electronic digital approach, based on the wavefront reconstruction method by matched filtering. 相似文献
4.
5.
The fundamental role of the assumption of plane wave ultrasonic propagation in attenuation and scattering measurements on soft tissues is discussed. The evidence for and against the validity of the assumption is shown to be inconclusive. An experimental procedure for direct assessment, by measurement of the ultrasonic amplitude and phase fluctuations occurring after an interrogating plane wave has passed through a tissue specimen, is described. The phase measurements impose significant demands on the mechanical precision, temperature stability and electronic timing capabilities of the measurement system. Measurements are reported on two specimens of fresh beef liver. One exhibited significant fluctuations of amplitude and phase which were reduced by 50% when the effects of thickness variations in the specimen were removed. The other specimen exhibited relatively small fluctuations. The feasibility of making such measurements has been demonstrated and the detailed features of the experimental procedure-which requires considerable care-have been outlined. Although more measurements are needed for definitive conclusions, these will require the development of a reliable technique for determining the presence of gaseous microbubbles in tissue in vitro. The preliminary conclusion that some samples of liver may exhibit low levels of wavefront disruption is consistent with recent evidence in the literature. 相似文献
6.
Chung S. H. 《显形杂志》2003,6(2):95-106
Several applications of laser diagnostic techniques to visualize combustion phenomena are presented, including reactive Mie
scattering for flow, Rayleigh and Raman spectroscopy for major species, laser-induced fluorescence for minor species, and
laser extinction, scattering, and laser-induced incandescence for soot. These techniques have been applied to diffusion flame
oscillation, a recirculation zone in a burner, laminar and turbulent lifted flames, flame propagation along a vortex tube,
and soot zone characteristics, to demonstrate the usefulness of the techniques to provide a better understanding of physical
mechanisms. 相似文献
7.
8.
9.
The film condensation of vapor on a cooled, downward-facing surface is a complex dynamic fluid phenomenon. This paper will describe the theoretical basis, instrumentation approach, and experimental results for a method for ultrasonic monitoring of film condensation. The ultrasound measurement system utilizes a 10 MHz broadband contact transducer, operating in pulse-echo mode. By appropriate signal processing, condensation layers over a wide thickness range, from much less than a wavelength to several wavelengths, can readily be measured. 相似文献
10.
11.
A device using a three-electrode electrochemical cell (referred to as an ECNMR cell) was successfully constructed that could be used in a standard 5mm NMR probe to acquire high-resolution NMR spectra while the working electrode was held at a constant electrical potential. The working electrode was a 20 nm thick gold film thermally coated on the outside of an inner 3mm glass tube. An underlayer consisting of (3-mercaptopropyl)trimethoxy-silane was coated on the glass surface in order to improve its adhesion to gold. Tests showed prolonged life of the gold film. Details of the design and construction of the ECNMR cell are described. The ECNMR cell could be routinely used in a multi-user service high-resolution NMR instrument under oxygen-free conditions in both aqueous and non-aqueous solvents. Different approaches were applied to suppress the noise transmitted between the potentiostat and the NMR spectrometer. These approaches were shown to be effective in reducing background noise in the NMR spectra. The electrochemical and NMR performance of the ECNMR cell is presented. The reduction of 1,4-benzoquinone in both aqueous and non-aqueous solvents was used for testing. The evolution of the in situ ECNMR spectra with time demonstrated that use of the ECNMR cell was feasible. Studies of caffeic acid and 9-chloroanthracene using this ECNMR cell were undertaken to explore its applications, such as monitoring reactions and studying their reaction mechanisms. 相似文献
12.
时间反转技术在超声无损检测中的应用非常广泛,它可以忽略介质的非均匀性及初始信号源的位置,能够在时间和空间上聚焦超声波,实现对介质缺陷的聚焦检测。基于LabVIEW图形化编程软件,结合计算机、信号发生器、示波器、超声换能器、GPIB等的使用,对超声检测系统实验平台进行了构建,实现了超声信号的发射、接收以及时间反转一系列的信号处理过程。系统工作过程中,采用了三种不同的时间反转技术:经典时间反转技术(Time Reversal:TR)、反向滤波技术(Inverse Filter:IF)及1位处理技术(1Bit Processing),来实现信号的聚焦。实验验证该系统可以有效的实现时间反转超声检测过程中对信号的激励、接收、处理和存储等功能,有良好的精确性和适用性。 相似文献
13.
本介绍在光热红外检测的基础上发展的超声红外热像技术。该技术利用超声脉冲作为激发源,当超声脉冲在试样上传播的过程中遇到裂纹等缺陷时,缺陷引起超声附加衰减而局部升温。利用红外照相机获取试样表面的温度分布,可显示裂纹等缺陷。超声红外热像技术发挥了超声和红外技术的优点,可实时地检测裂纹等缺陷,在无损评价和检测中有广泛应用。 相似文献
14.
In recent years, there has been an increasing interest in the design of biomaterials for cartilage tissue engineering. This type of materials must meet several requirements. In this study, we apply ultrasound to prepare a compatibilized blend of polyelectrolyte complexes (PEC) based on carboxymethyl cellulose (CMC) and chitosan (CHI), in order to improve stability and mechanical properties through the inter-polymer macroradicals coupling produced by sonochemical reaction. We study the kinetic of the sonochemical degradation of each component in order to optimize the experimental conditions for PEC compatibilization. Scaffolds obtained applying this methodology and scaffolds without ultrasound processing were prepared and their morphology (by scanning electron microscopy), polyelectrolyte interactions (by FTIR), stability and mechanical properties were analyzed. The swelling kinetics was studied and interpreted based on the structural differences between the two kinds of scaffolds. In addition we evaluate the possible in vitro cytotoxicity of the scaffolds using macrophage cells in culture. Our results demonstrate that the ultrasound is a very efficient methodology to compatibilize PEC, exhibiting improved properties compared with the simple mixture of the two polysaccharides. The test with murine macrophage RAW 264.7 cells showed no evince of cytotoxicity, suggesting that PEC biomaterials obtained under ultrasound conditions could be useful in the cartilage tissue engineering field. 相似文献
15.
导航卫星的上行注入与测距性能是卫星导航系统服务精度一个重要保证,设计了一种导航卫星的上行注入与测距性能测试系统;该系统以控制处理计算机为核心,并结合了专用设计的基准频率发生器模块、基准时间发生器模块、注入信号发生器模块和通用商业化仪器,能实时动态地模拟导航卫星在轨期间接收地面注入信号的情形,完成导航卫星上行注入性能测试中电文信息的生成和比对以及上行测距性能测试;该测试系统稳定、灵活,测量精度高,而且可以通过修改测试软件参数来满足新的测试要求,便于测试系统的升级改造。 相似文献
16.
17.
Anette Salomonsson Rodrigo M. Petoral Jr. Kajsa Uvdal Christian Aulin Per-Olov Käll Lars Ojamäe Michael Strand Mehri Sanati Anita Lloyd Spetz 《Journal of nanoparticle research》2006,8(6):899-910
In this project, we have explored RuO2 and Ru nanoparticles (∼
∼10 and ∼
∼5 nm, respectively, estimated from XRD data) to be used as gate material in field effect sensor devices. The particles were synthesized by wet chemical procedure. The capacitance versus voltage characteristics of the studied capacitance shifts to a lower voltage while exposed to reducing gases. The main objectives are to improve the selectivity of the FET sensors by tailoring the dimension and surface chemistry of the nanoparticles and to improve the high temperature stability. The sensors were characterized using capacitance versus voltage measurements, at different frequencies, 500 Hz to 1 MHz, and temperatures at 100–400°C. The sensor response patterns have been found to depend on operating temperature. X-ray photoelectron spectroscopy (XPS) analyses were performed to investigate the oxidation state due to gas exposure. Quantum-chemical computations suggest that heterolytic dissociative adsorption is favored and preliminary computations regarding water formation from adsorbed hydrogen and oxygen was also performed. 相似文献
18.
19.
20.
George A. Boyarko Chih-Jen Sung Steven J. Schneider 《Proceedings of the Combustion Institute》2005,30(2):2481-2488
The present investigation addresses the need to understand the physics and chemistry involved in propellant combustion processes in micro-scale combustors for propulsion systems on micro-spacecraft. These spacecraft are planned to have a mass less than 50 kg with attitude control estimated to be in the 1–10 mN thrust class. Micro-propulsion devices behave differently than macro-scale devices because of the differences in magnitude of flow rates and heat transfer. Reducing the combustor size increases the relative surface area, increasing the heat loss, and as combustors are continuously reduced in size, they approach the quenching dimensions of the propellants. Combustors of this size are expected to significantly benefit from surface catalysis processes. A miniature flame tube apparatus is chosen for this study because microtubes can be easily fabricated from known catalyst materials, and their simplicity in geometry can be used in fundamental simulations for validation purposes. Experimentally, we investigated the role of catalytically active surfaces within 0.4 and 0.8 mm internal diameter microtubes, with special emphases on ignition processes in fuel rich gaseous hydrogen and gaseous oxygen. Calculations of flame thickness and reaction zone thickness predict that the diameters of our test apparatus are below the quenching diameter of the propellants in most atmospheric test conditions. The temperature and pressure rise in resistively heated platinum microtubes and the exit hydrogen concentration were used as an indication of exothermic reactions. Data on imposed heat flux/preheat temperature required to achieve ignition versus mass flow rate are presented. With a plug flow model, the experimental conditions were simulated with detailed gas-phase chemistry and surface kinetics. Computational results, in general, support the experimental findings. 相似文献