PLIF法定量测量甲烷-空气火焰二维温度场分布

利用平面激光诱导荧光(PLIF)技术,通过选择适合的OH自由基激励线,定量测量了甲烷-空气燃烧火焰的二维温度场分布。给出炉面中心上方火焰温度随离炉面高度的变化和距炉面12 mm高处沿炉面水平方向变化的实验测量结果并进行了讨论与分析。与利用相干反斯托克斯喇曼散射（CARS）技术进行测温的实验结果相比,该测量的相对不确定度优于5％。     

PLIF法定量测量甲烷-空气火焰二维温度场分布

利用平面激光诱导荧光(PLIF)技术,通过选择适合的OH自由基激励线,定量测量了甲烷-空气燃烧火焰的二维温度场分布。给出炉面中心上方火焰温度随离炉面高度的变化和距炉面12 mm高处沿炉面水平方向变化的实验测量结果并进行了讨论与分析。与利用相干反斯托克斯喇曼散射（CARS）技术进行测温的实验结果相比,该测量的相对不确定度优于5％。     

光场强度分布测量中CCD噪声的校正

为了有效抑制CCD测量噪声带给激光对比度分布测量的影响,基于对比度测量模型,利用CCD测量噪声的先验知识及其输出观测值,给出了CCD噪声的校正方法。与现有计算方法的比较表明,该方法可以有效抑制CCD测量噪声带给测量的影响,其扩展不确定度从0.6%降低至0.3%,降低了测量不确定度,提高了测量的置信度。     

光场强度分布测量中CCD噪声的校正北大核心CSCD

为了有效抑制CCD测量噪声带给激光对比度分布测量的影响,基于对比度测量模型,利用CCD测量噪声的先验知识及其输出观测值,给出了CCD噪声的校正方法。与现有计算方法的比较表明,该方法可以有效抑制CCD测量噪声带给测量的影响,其扩展不确定度从0.6%降低至0.3%,降低了测量不确定度,提高了测量的置信度。     

Acoustic noise simulation and measurement of a gradient insert in a 4 T MRI

High speed switching of current in gradient coils within high magnetic field strength magnetic resonance imaging (MRI) scanners results in high acoustic sound pressure levels (SPL) in and around these machines. Many studies have already been conducted to characterize the sound field in and around MRIs and various methods have been investigated to attenuate the noise generated. In the work presented here a computational vibro-acoustic model was developed based on an iteratively modified and validated finite element (FE) model to characterize the acoustic noise properties of the gradient coil. The simulation results from the computational model were verified through experimental noise measurement for the gradient coil insert in a 4 T MRI scanner by using swept sinusoidal time waveform inputs. Comparisons show that the computational model predicts the noise characteristic properties extremely accurately. There are three dominant frequency bands where the SPL is much higher than those at other frequencies. The SPL in the horizontal direction is much higher than that in the vertical direction due to the excitation to the horizontally placed X coil. The SPL to the inner surface of the coil is higher than far from the inner surface, which proves that the acoustic noise is radiated from the inner surface and primarily caused by the normal vibration of the inner surface. Further verification was conducted by using two types of trapezoidal sequence inputs usually used, which is to simulate real scanning sequences for small animals. Again the accuracy of the developed model is verified. The validated acoustic computational model could be used as an effective method to predict the noise that would be produced by a coil in the design stage. Modification of the structural design or the excitation pulse could be performed to reduce the acoustic noise when the gradient coil is in scanning.     

HIFU温度场可视化测量初探

本实验用蓖麻油模拟人体环境、热敏打印纸作为记录载体,测量高强度聚焦超声(HIFU)治疗系统焦点附近的温度分布情况。实验中热敏打印纸显影所指示的温度已经达到HIFU治疗所需要的温度,实验的结果对进一步研究HIFU温度场分布有借鉴作用。     

Acoustic characteristics of a rocket combustion chamber: Radial baffle effects

This paper describes methods used for determining the characteristic acoustic modes and frequencies of a liquid-propellant rocket-motor combustion chamber and effects of radial baffles on the chamber’s acoustic field. A multi-point sensing experimental setup, including stationary and moving sensors, was used to measure characteristic frequencies and mode shapes of a combustion chamber. A new technique based on the comparison of signal phase angles from stationary sensors to that of a moving sensor was used to map complex characteristic mode shapes of a combustor. A three-dimensional Helmholtz acoustic solver was also developed using an efficient finite volume approach for complex geometries to simulate the acoustic field inside a combustor. Using this approach the effects of the convergent section of the nozzle and the number of radial baffles on the chamber’s dominant acoustic modes with no mean flow were investigated. We have shown that the classical reduction of characteristic frequency of tangential modes caused by radial baffles is due to longitudinalization of tangential modes and is a function of the blade length and weakly dependent on the number of blades. Also, conjugate spinning modes are decoupled and do not spin in any baffled combustor, independent of the number of blades. On the other hand the converging nozzle section of a combustion chamber modifies pure longitudinal modes in the radial direction and pure tangential modes in the longitudinal direction. Existence of some mixed tangential-longitudinal modes in a combustor is dependent on the ratio of the nozzle throat diameter to the combustor head plate diameter.     

非均匀海洋环境噪声中的匹配场处理舰船辐射噪声级估计方法

在实际舰船辐射噪声测量过程中,受非均匀海洋环境噪声的影响,导致常规测量方法的性能急剧下降,基于此,提出了一种非均匀海洋环境噪声背景中的垂直阵舰船辐射噪声测量方法。根据水声信道传播理论,建立了由海面多个空时独立均匀分布噪声源构成的非均匀背景噪声场模型,推导了非均匀海洋环境噪声场中垂直阵舰船辐射噪声估计的理论公式。针对典型的浅海水声信道,进行计算机仿真实验,分析了该方法的测量性能并与常规匹配场测量方法进行对比,结果表明:(1)该方法能有效克服非均匀海洋环境噪声对测量结果的影响,测量误差较小;(2)相同测量条件下,该方法测量性能优于常规匹配场舰船辐射噪声级测量方法;(3)当信噪比满足一定要求时,测量得到的声源级与实际声源级相比,误差小于1 dB。     

非均匀海洋环境噪声中的匹配场处理舰船辐射噪声级估计方法

在实际舰船辐射噪声测量过程中,受非均匀海洋环境噪声的影响,导致常规测量方法的性能急剧下降,基于此,提出了一种非均匀海洋环境噪声背景中的垂直阵舰船辐射噪声测量方法。根据水声信道传播理论,建立了由海面多个空时独立均匀分布噪声源构成的非均匀背景噪声场模型,推导了非均匀海洋环境噪声场中垂直阵舰船辐射噪声估计的理论公式。针对典型的浅海水声信道,进行计算机仿真实验,分析了该方法的测量性能并与常规匹配场测量方法进行对比,结果表明:(1)该方法能有效克服非均匀海洋环境噪声对测量结果的影响,测量误差较小;(2)相同测量条件下,该方法测量性能优于常规匹配场舰船辐射噪声级测量方法;(3)当信噪比满足一定要求时,测量得到的声源级与实际声源级相比,误差小于1 dB。     

Energy diffusion in a strong noise field

It is shown that, under the action of a perturbation with a continuous frequency spectrum, the rate of the energy diffusion of a quantum oscillator is described by an expression that formally follows from the Fermi golden rule, even when the conditions of the validity of this rule are violated, that is, in the parameter range where the transition rate is comparable to the frequency of transition between the system levels or exceeds it. This circumstance provides the quantum-classical correspondence for the energy diffusion rate in the quasi-classical domain.     

Finite temperature field theory and quantum noise in inductively coupled LRC circuits

Finite temperature (0 ⩽ T < ∞) field (FTF) theory with an effective spectral lagrangian density formulation is used to study quantum noise in inductively coupled LRC circuits. Analytical solutions and numerical results for the finite second moments at temperature T which satisfy the uncertainty principle bound are given. From the numerical results, one can see the presence of a squeezed quantum state which depends upon the strength of the mutual inductance between the coupled circuits.     

声强测量技术在水下结构辐射噪声近场测量中的应用

本文介绍了强测量技术在水下结构辐射近场测量中的实际测量系统，特别是水下声系统的扫描平面的实现方法及定位误差控制方法，最后讨论和分析了实际测量结果，从而说明该系统用水下声强测量是可行的。     

Acoustic streaming in a sound field near a free boundary

Stationary acoustic streaming that occurs near the free boundary of a compressible viscous liquid in the field of a standing sound wave excited along this boundary is theoretically investigated.     

Acoustic transparency of organic conductors in a magnetic field

It is predicted that organic conductors have high acoustic transparency in high magnetic fields. The effect is shown to be due to the two-dimensional nature of the electron energy spectrum. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 12, 845–848 (25 December 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Acoustic excitation of a square plate by turbulent flow noise

An experiment was conducted to measure the characteristics of flow noise in a bounded system with forced circulation. The flow noise facility is described herewith. Vortex shedding in the conducting rectangular ducting was experimentally controlled by the insertion of cylinders of various diameter and pitch perpendicular to the flow. The sound pressure level exciting an instrumented square plate parallel with the flow direction was measured, as well as the plate response.