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921.
In situ measurement on nonuniform velocity distributionin external detonation exhaust flow by analysis ofspectrum features using TDLAS 下载免费PDF全文
Instantaneous and precise velocity sensing is a critical part of research on detonation mechanism and flow evolution.This paper presents a novel multi-projection tunable diode laser absorption spectroscopy solution,to provide a real-time and reliable measurement of velocity distribution in detonation exhaust flow with obvious nonuniformity.Relations are established between overlapped spectrums along probing beams and Gauss velocity distribution phantom according to the frequency shifts and tiny variations in components of light-of-sight absorbance profiles at low frequencies analyzed by the fast Fourier transform.With simulated optical measurement using H2O feature at 7185.6 cm-1 carried out on a phantom generated using a simulation of two-phase detonation by a two-fluid model,this method demonstrates a satisfying performance on recovery of velocity distribution profiles in supersonic flow even with a noise equivalent absorbance up to 2×10-3.This method is applied to the analysis of rapidly decreasing velocity during a complete working cycle in the external flow field of an air-gasoline detonation tube operating at 25 Hz,and results show the velocity in the core flow field would be much larger than the arithmetic average from traditional tunable diode laser doppler velocimetry.This proposed velocity distribution sensor would reconstruct nonuniform velocity distribution of high-speed flow in low cost and simple operations,which broadens the possibility for applications in research on the formation and propagation of external flow filed of detonation tube. 相似文献
922.
C. F. Liu Y. Tang 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,70(2):193-199
We provide a mixing model to explore the metastable state
and the macroscopic quantum tunneling (MQT) of binary mixtures. For , we first observe the two condensates form the
symmetry-breaking state (SBS) and then suddenly transfer to the
symmetry-preserving state (SPS) through the MQT. The SBS is shown to be the
metastable state in our system. We find the MQT does not spontaneously
arise. The inducement mechanism is the damping but not the excitations. The
damping mechanism can also control the lifetime and the tunneling decay rate
of the SBS. Finally, we further present the origin of these phenomena by
examining the energy of the system. 相似文献
923.
The rarefied effect of gas flow in microchannel is significant and cannot be well described by traditional hydrodynamic models. It has been known that discrete Boltzmann model(DBM) has the potential to investigate flows in a relatively wider range of Knudsen number because of its intrinsic kinetic nature inherited from Boltzmann equation.It is crucial to have a proper kinetic boundary condition for DBM to capture the velocity slip and the flow characteristics in the Knudsen layer. In this paper, we present a DBM combined with Maxwell-type boundary condition model for slip flow. The tangential momentum accommodation coefficient is introduced to implement a gas-surface interaction model.Both the velocity slip and the Knudsen layer under various Knudsen numbers and accommodation coefficients can be well described. Two kinds of slip flows, including Couette flow and Poiseuille flow, are simulated to verify the model.To dynamically compare results from different models, the relation between the definition of Knudsen number in hard sphere model and that in BGK model is clarified. 相似文献
924.
邹江 《原子与分子物理学报》2020,37(4)
采用基于密度泛函理论的第一性原理计算方法,对未掺杂及Ce掺杂CrSi2的电子结构和光学性质进行理论计算。计算结果表明,未掺杂CrSi2是间接带隙半导体,其禁带宽度为0.392 eV,掺杂Ce元素,仍然是间接半导体,带隙宽度下降为0.031eV。未掺杂CrSi2在费米能级附近主要由Cr-5d、Si-3p态贡献。Ce掺杂后在费米能级附近主要由Cr-5d轨道,Ce-4f轨道,C-2p,Si-3p轨道贡献,掺杂后电导率提高。未掺杂CrSi2有两个介电峰,掺杂后,只有一个介电峰。未掺杂CrSi2,在能量为6.008处吸收系数达到最大值,掺杂后在能量为5.009eV处,吸收系数达到最大值。 相似文献
925.
介绍了 HL-2M 装置冷却水系统的组成以及各子系统的循环流程、运行原理和运行参数。 相似文献
926.
A stable increase by as much as 108 in the conductivity of amorphous indium oxide to σ≥ 103Ω-1 cm−1 can be achieved by ultraviolet photoreduction. This treatment also increases the absorption coefficient, α(hυ), by up to
a factor of 103 for hυ <1.5 eV due to free carrier absorption and causes a 0.1 eV shift of the absorption edge to the blue. These changes
are controlled by the Fermi level, EF, which is presumably determined by doping due to oxygen vacancies. A diffusion constant
D >3 x 10−12 cm2/s for oxygen at 300K is determined from a constant flow experiment. Oxygen diffusion is verified by secondary ion mass spectrometry
with 18O. The functions α(hυ) and σ(T) are simulated as EF is varied using a simple density of states model appropriate for amorphous semiconductors. These simulations qualitatively
agree with the experimental data if transitions from the conduction band tail to the conduction band are assumed to be forbidden. 相似文献
927.
928.
929.
930.
图像特征匹配是视觉里程计的重要环节,针对视觉图像序列特征点匹配中存在的匹配精度低问题,提出一种融合金字塔特征光流与角点特征的精确快速图像特征匹配算法。算法首先利用ORB(二进制定向简单描述符)算法快速提取图像特征点,然后融合金字塔Lucas-Kanade特征光流的追踪特性,使用局部特征窗口计算图像特征点位移矢量。接着针对图像特征的匹配对齐问题以及特征丢失问题,算法采用K最近邻半径搜索作为特征滤波器移除混淆的匹配,最后使用RANSAC(Random Sample Consensus)算法剔除冗余误匹配点对,提高匹配率。通过多组实验数据对比,该算法的图像特征匹配率可达到98%。对比传统的ORB特征匹配算法,该算法在实时性和图像特征匹配精度上均有显著提高。 相似文献