共查询到20条相似文献,搜索用时 375 毫秒
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利用二维粒子模拟程序EPOCH验证了超快电子束探针诊断受激拉曼散射产生的静电波的可行性。结果表明,电子束探针穿过静电波电场后会在电子束探针的横向上产生密度调制,密度调制呈周期性分布且沿静电波的传播方向移动,密度调制的波数对应静电波的波数且移动速度对应静电波的相速度,因此特定条件下可用于反推电子的温度、密度等信息。在诊断静电波的过程中,电子束探针的束长必须小于静电波的波长或者诊断设备的曝光时间必须小于静电波的周期。本研究提供了一种新型的直接诊断静电波和电子温度、密度的方法,对于推动受激拉曼散射等激光等离子体不稳定性的实验研究具有重要意义。 相似文献
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对长度为45 cm的短放电管螺旋波放电等离子体进行了Langmuir探针、原子发射光谱以及集成电荷耦合检测器(ICCD)检测诊断,研究螺旋波等离子体的放电特性.Langmuir探针数据显示电子密度在射频功率增加过程中出现两次大幅增长,由此确认了放电模式的转换及螺旋波放电模式的出现.发射光谱测量结果与Langmuir探针测量的电子密度数据一致,发现Ar原子和Ar离子的谱线强度与放电模式变化有着密切相关性.而通过对不同放电模式的ICCD测量,获得射频功率吸收因放电模式转变而变化的方式,认为放电模式转换时电子行为和能量传递方式也发生着变化. 相似文献
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使用PSD作为大口径光学元件表面加工质量的评价参数,针对不同的波前调制进行了初步的模拟计算,得到了不同调制频率和不同调制深度情况下的PSD曲线变化情况。当调制频率不同时,PSD曲线的突变部分会发生相应的频移,调制频率高则突变发生在空间频率较高的频段,同时PSD峰值不变。相对应调制深度不同时,PSD曲线的突变部份峰值发生变化,调制深度大则峰值大,与此同时峰值出现的位置不会发生变化。计算和分析结果表明PSD分析结果能够在频率域反应出元件表面受到的不同程度的调制信息。 相似文献
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Queralt-Martín M Pradas M Rodríguez-Trujillo R Arundell M Corvera Poiré E Hernández-Machado A 《Physical review letters》2011,106(19):194501
Rare events appear in a wide variety of phenomena such as rainfall, floods, earthquakes, and risk. We demonstrate that the stochastic behavior induced by the natural roughening present in standard microchannels is so important that the dynamics for the advancement of a water front displacing air has plenty of rare events. We observe that for low pressure differences the hydrophobic interactions of the water front with the walls of the microchannel put the front close to the pinning point. This causes a burstlike dynamics, characterized by series of pinning and avalanches, that leads to an extreme-value Gumbel distribution for the velocity fluctuations and a nonclassical time exponent for the advancement of the mean front position as low as 0.38. 相似文献
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《Physica D: Nonlinear Phenomena》2003,174(1-4):168-175
Recent theoretical work has shown that so-called pulled fronts propagating into an unstable state always converge very slowly to their asymptotic speed and shape. In the light of these predictions, we reanalyze earlier experiments by Fineberg and Steinberg on front propagation in a Rayleigh–Bénard cell. In contrast to the original interpretation, we argue that in the experiments the observed front velocities were some 15% below the asymptotic front speed and that this is in rough agreement with the predicted slow relaxation of the front speed for the time scales probed in the experiments. We also discuss the possible origin of the unusually large variation of the wavelength of the pattern generated by the front as a function of the dimensionless control parameter. 相似文献
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Cellular cell pattern evolution of cylindrically-diverging detonations is numerically simulated successfully by solving two-dimensional Euler equations implemented with an improved two-step chemical kinetic model. From thesimulation, three cell bifurcation modes are observed during the evolution and referred to as concave front focusing, kinked and wrinkled wave front instability, and self-merging of cellular cells. Numerical research demonstrates that the wave front expansion resulted from detonation front diverging plays a major role in the cellular cell bifurcation, which can disturb the nonlinearlyself-sustained mechanism of detonations and finally lead to cell bifurcations. 相似文献
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Jeroen A.S. Witteveen 《Journal of computational physics》2010,229(7):2719-2739
A second order front tracking method is developed for solving the hyperbolic system of Euler equations of inviscid fluid dynamics numerically. Meshless front tracking methods are usually limited to first order accuracy, since they are based on a piecewise constant approximation of the solution. Here second order convergence is achieved by deriving a piecewise linear reconstruction of the piecewise constant front tracking solution. The linearization is performed by decomposing the front tracking solution into its wave components and by linearizing the wave solutions separately. In order to construct a physically correct linearization, the physical phenomena of the front are taken into account in terms of the front types of the previously developed improved front interaction model. This front interaction model is also extended to include front numbers used in the wave decomposition. It is illustrated numerically for Sod’s Riemann problem, the two interacting blast waves problem, and a two-dimensional supersonic airfoil flow validation study that the proposed front tracking method achieves second order convergence also in the presence of strong discontinuities and their interactions. 相似文献
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Presented are results of studying the dynamics of evaporation front propagation in mixtures of R21/R114 freons with the concentration of volatile component R114 in the range of 0–0.22 under saturation, as well as at subcooling to 20 K. The dependence of the front velocity on the temperature difference with a stepwise heat release is obtained; spectral analysis of oscillation characteristics of the evaporation front interfacial boundary is performed. It is shown that the difference in the dynamics of the evaporation front in these experiments depends on the development of instability at the interfacial boundary of the front. 相似文献
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The problem of front propagation in a stirred medium is addressed in the case of cellular flows in three different regimes: slow reaction, fast reaction and geometrical optics limit. It is well known that a consequence of stirring is the enhancement of front speed with respect to the nonstirred case. By means of numerical simulations and theoretical arguments we describe the behavior of front speed as a function of the stirring intensity, U. For slow reaction, the front propagates with a speed proportional to U(1/4), conversely for fast reaction the front speed is proportional to U(3/4). In the geometrical optics limit, the front speed asymptotically behaves as U/ln U. (c) 2002 American Institute of Physics. 相似文献
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We investigate flux front penetration in a disordered type-II superconductor by molecular dynamics simulations of interacting vortices and find scaling laws for the front position and the density profile. The scaling can be understood by performing a coarse graining of the system and writing a disordered nonlinear diffusion equation. Integrating numerically the equation, we observe a crossover from flat to fractal front penetration as the system parameters are varied. The value of the fractal dimension indicates that the invasion process is described by gradient percolation. 相似文献
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静态傅里叶变换红外光谱仪的公差分析 总被引:1,自引:0,他引:1
由于光谱分辨率或光谱信噪比只能作为光谱仪干涉系统的性能评价指标,但不能用于光学系统的公差分析与优化,所以将系统分为三个子系统:前置光学系统、干涉系统与后置光学系统,分别采用不同的评价标准分析系统公差。前置光学系统采用波像差为评价标准,给出波像差与光谱噪声的关系,分析误差对波像差的影响,间接给出各种误差对系统性能的影响。干涉系统直接采用光谱噪声作为评价标准,可直接给出各种误差对系统性能的影响。后置光学系统采用光斑尺寸作为评价标准。通过这种方法,计算出三个子系统的灵敏度矩阵,并且给出了前置光学系统与后置光学系统的公差分配。 相似文献
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The local heating of an absorbing medium by an ultrasonic beam with a conjugate wave front has been experimentally demonstrated. Plastisol, which is a polymeric material close in acoustic properties to biological tissue, is used as the medium. An ultrasonic heating of 7.2°C has been obtained in a time of about 100 s when the sample equipped with a thermocouple is placed between a focused piezoelectric transducer emitting a “probe wave” with a frequency of 5.0 MHz and a system that reverses the ultrasonic wave front with amplification. The characteristic features of heating by ultrasonic beams with the conjugate front, as well as the prospects of applications of this effect in medicine and other fields, have been discussed. 相似文献