共查询到20条相似文献,搜索用时 0 毫秒
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Chu M 《Physical review letters》1996,76(24):4632-4635
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An Y 《Ultrasonics》2006,44(Z1):e439-e444
With the new accommodation coefficient of water vapor evaluated by molecular dynamics model, the maximum temperature of a sonoluminescing bubble calculated with the full partial differential equations easily reaches few tens of thousands degrees. Though at this temperature the gas is weakly ionized (10% or less), the gas density inside a sonoluminescing bubble at the moment of the bubble's flashing is so high that there still forms a dense plasma. The light emission of the bubble is calculated by the plasma model which is compared with that by the bremsstrahlung (electron-ion, electron-neutral atom) and recombination model. The calculation by the two models shows that for the relatively low maximum temperature (< 30,000 K) of the bubble, the pulse width is independent of the wavelength and the spectrum deviates the black body radiation type; while for the relatively high maximum temperature (approximately 60,000 K), the pulse width is dependent of the wavelength and the spectrum is an almost perfect black body radiation spectrum. The maximum temperature calculated by the gas dynamics equations is much higher than the temperature fitted by the black body radiation formula. 相似文献
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The spectral shape and observed sonoluminescence emission from Xe bubbles in concentrated sulfuric acid is consistent only with blackbody emission from a spherical surface that fills the bubble. The interior of the observed 7000 K blackbody must be at least 4 times hotter than the emitting surface in order that the equilibrium light-matter interaction length be smaller than the radius. Bright emission is correlated with long emission times (approximately 10 ns), sharp thresholds, unstable translational motion, and implosions that are sufficiently weak that contributions from the van der Waals hard core are small. 相似文献
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Yasui K 《Ultrasonics》2002,40(1-8):643-647
Computer simulations of bubble oscillations in water are performed for various noble gases taking into account the segregation of water vapor and noble gas inside a collapsing bubble, which was predicted by Storey and Szeri [J. Fluid Mech. 396 (1999) 203]. It is clarified that the number of water vapor molecules dissociated inside a collapsing bubble is larger for heavier noble gases because of the lower thermal conductivity and the segregation of vapor and noble gas. It is also clarified that the temperature inside a helium bubble at the collapse increases considerably by the mixture segregation because a lesser amount of vapor is trapped inside a collapsing bubble. It is also clarified that multibubble sonoluminescence (MBSL) from heavier noble gases is brighter because of the lower ionization potential which results in the higher electron density and stronger plasma emissions. 相似文献
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The size of the light-emitting region is a key parameter toward understanding the light-emitting processes in a sonoluminescing bubble. Here we present measurements of interference effects from particles with a diameter of approximately 2 microm situated 6-10 microm from a sonoluminescing bubble. From the angular size of the pattern and from an estimated distance to the particles we conclude that the light-emitting region of a sonoluminescing bubble is smaller than commonly believed [see, e.g., Nature (London) 398, 402 (1999)]. We argue that an upper limit of the size of the light-emitting region is approximately 200 nm. 相似文献
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Weninger KR Evans PG Putterman SJ 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》2000,61(2):R1020-R1023
Application of time correlated single photon counting to pulsed Mie scattering enables one to resolve changes in light scattering to better than 50 ps. This technique is applied to the highly nonlinear motion of a sonoluminescing bubble. Physical processes, such as outgoing shock wave emission, that limit the interpretation of the data are measured with a streak camera and microscopy. Shock speeds about 6 km/s have been observed. 相似文献
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提出了一个单气泡声致发光的简单计算模型.这个模型是在均匀压强近似下,考虑质量和温度在气泡内的非均匀分布,同时考虑了水蒸气在气泡壁上的凝结与蒸发以及水蒸气在气泡内相对惰性气体的质量扩散.通过Saha方程估算气体电离密度,利用电子与离子、电子与中性粒子的轫致辐射,电子与离子的复合辐射公式估算气泡的辐射强度.不考虑化学反应,计算了不同水温时的气泡发光强度,发现当水温在0 ℃时轫致辐射发光模型比较符合实验结果,水温升高时,如水温为20 ℃或以上,轫致辐射发光模型的计算与实验结果出现数量级差别.考虑化学反应,轫致辐射发光模型的计算则总是比实验结果低2个数量级. 相似文献
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Flannigan DJ Hopkins SD Camara CG Putterman SJ Suslick KS 《Physical review letters》2006,96(20):204301
The average pressure inside a sonoluminescing bubble in sulfuric acid has been determined by two independent techniques: (1) plasma diagnostics applied to Ar atom emission lines, and (2) light scattering measurements of bubble radius vs time. For dimly luminescing bubbles, both methods yield intracavity pressures approximately 1500 bar. Upon stronger acoustic driving of the bubble, the sonoluminescence intensity increases 10,000-fold, spectral lines are no longer resolved, and radius vs time measurements yield internal pressures > 3700 bar. Implications for a hot inner core are discussed. 相似文献
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《声学学报:英文版》2001,(1)
1 IntroductionThe phenomenon of Single Bubble Sonoluminescence (SBSL) has been discovered since1990[l], many eXPerimental results have been published[2--5], and these results show the basicimage of SBS as follows: An air bubble (typical radius is 5 pmLcan be trapped at the velocitynode of the acoustic standing wave in Water, and in a p.rha of sound wavet the bubble isexpanded (the radius can reach about 40 Urn), and then it is compressed rapidly, as compressedto near Van der Waals volume… 相似文献
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Previous works on single bubble sonoluminescence in sulfuric acid solutions have stressed the fact that the sonoluminescence (SL) emissions are the highest ever found, but at the same time the bubble moves in orbits. We have fixed the SL bubble spatially and at the same time we have reached higher SL emissions using another harmonic acoustic signal to produce the acoustic excitation. Multiple harmonic excitation produces up to a fourfold increase in SL emissions, reaching the peak value of about 40 microW for a moving bubble and 15 microW for a nonmoving bubble. The ability to have a bright stationary bubble also opens new research opportunities. In particular, we develop a new method to measure the absolute radius evolution of the bubble that exploits this stability. 相似文献
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Pulsed lasers are being widely used in industry for their high precision and low cost in material processing. In order to understand the laser machining mechanism, a thermal analysis of the process is of utmost importance. In the present study, heat transfer mechanisms relevant to pulsed laser heating is solved numerically using the Kinetic Theory approach for different types of laser pulses. A comparison between the temperature profiles developed due to different pulses is also carried out. In the heat transfer model, conduction and convection due to melting and evaporation are considered. The laser pulse profiles introduced in the analysis are selected as appropriate to laser machining processes. Stainless steel is selected as the heat transfer medium. 相似文献
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The dynamical motion of sonoluminescing bubbles formed from a mixture of water and hydrogen gas indicates that these bubbles contain hydrogen. Their spectrum is well matched by an ideal 6000 K blackbody radiating from a surface with a radius less than 1/4 microm. According to this model, the state of matter inside the collapsed bubble is so stressed that the photon mean free path is much smaller than 1 microm. Implications for various theories of the light-emitting mechanism and the role of chemical reactions are discussed. 相似文献
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Laser bubble detection based on optical photography is widely used in industrial areas such as air tightness measurements. However, the precision of detection is severely affected by the degradation of detecting images. In order to enhance the visual quality of bubble detection, an image semiblind restoration method with edge regularization is applied along with the estimation of the dynamic modulation transfer function. We use objective-image quality metrics to limit the deconvolution iterations of the semiblind deconvolution algorithm. We compare the performance of the binary morphology filter. Improvement by the proposed method can be seen from the experimental results. It can be concluded that the proposed approach can effectively enhance quality and edge details of the laser bubble detecting images, so that greater precision can be achieved. 相似文献
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A reliable analytical expression for the potential of plasma waves with phase velocities near the speed of light is derived. The presented spheroid cavity model is more consistent than the previous spherical and ellipsoidal model and it explains the mono-energetic electron trajectory more accurately, especially at the relativistic region. As a result, the quasi-mono-energetic electrons output beam interacting with the laser plasma can be more appropriately described with this model. 相似文献