Talbot interferometry in measurements of the parameters of an axisymmetric turbulent jet

The Talbot effect has been adapted to measurement of the parameters of mixing in an axisymmetric turbulent helium jet flowing out into a submerged air space. A two-dimensional array of angles of refraction of light has been determined from the displacement of the image of unit Talbot elements in the reproduction plane of the time-averaged talbogram. The distribution of the average refractive index of a medium and the concentration of helium in the flow field have been calculated by means of the Abel transformation. Based on an analysis of the intensity distribution at the maxima of the Talbot image, it has been shown that the turbulence of this jet is locally inhomogeneous and anisotropic. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 94–99, September–October, 2006.     

阵列信号维纳滤波用于主动声呐图像增强处理

声呐图像的噪声背景抑制是提高水下目标检测能力的重要问题.针对声呐图像背景斑点噪声强、目标轮廓模糊、目标回波对比度低等问题,利用确定性目标回波信号与随机分布的干扰噪声之间的相关统计特性差异,采用基于最小均方差准则的阵列信号维纳滤波器,通过主动最小方差无畸变响应(Minimum Variance Distortionles...     

Region-of-interest reconstruction from noisy projections using fractal models and Wiener filtering

In this paper, we present a method for region-of-interest (ROI) tomography using noisy projections. A wavelet decomposition down to the coarsest level is done on the noisy signal. The signal at various levels is estimated using a Wiener filter. By assuming that the projections are 1/f processes, the Wiener filtering reduces to a scalar multiplication. Using the Wiener filter and regularity property of the wavelets, we combine the estimation and localisation of the noisy projections for ROI imaging. Experimental results are shown on Shepp-Logan phantom and actual CT images. The validity of the 1/f model for projections of real life images is also shown. The names of the authors are in alphabetical order     

Wind speed measurements of Doppler-shifted absorption lines using two-beam interferometry

Wind speed can be measured remotely, with varying degrees of success, using interferometry of Doppler-shifted optical spectra. Under favorable conditions, active systems using laser pulse backscatter are capable of high resolution; passive systems, which measure Doppler shifts of atmospheric emission lines in the mesosphere, have also been shown. Two-beam interferometry of Doppler-shifted absorption lines has not been previously investigated; we describe such an effort here. Even in a well-defined environment, measuring absorption line Doppler shifts requires overcoming several technical hurdles in order to obtain sensitivity to wind speeds on the order of 10 m/s. These hurdles include precise knowledge of the shape of the absorption line, tight, stable filtering, and understanding precisely how an interferometer phase should respond to a change in the absorption profile. We discuss the instrument design, a Michelson interferometer and Fabry-Perot filter, and include an analysis of how to choose the optimal optical path difference of the two beams for a given spectrum and filter. We discuss two beam interferometric measurements of emission line and absorption line Doppler shifts, and include an illustration of the effects of filtering on LIDAR Doppler interferometry. Finally, we discuss the construction and implementation of a Michelson interferometer used to measure Doppler shifts of oxygen absorption lines and present results obtained with 5 m/s wind speed measurement precision. Although the theoretical shot noise limited Doppler wind speed measurement of the system described can be less than 1 m/s, the instrument's resolution limit is dominated by residual filter instability. Application of absorption line interferometry to determine atmospheric wind speeds remains problematic.     

Optimal burn-in policy by using an integrated Wiener process

The conventional burn-in test, which only collects go/no go (or time-to-failure) data over short testing periods becomes rather ineffective for highly reliable products. This decision problem can be solved if there exists a suitable quality characteristic whose degradation over time can be related to the product's lifetime. An innovative approach to determine the burn-in policy by using a suitable degradation model has been suggested in the literature. However, a major disadvantage of this procedure is that it only uses information contained in current degradation data, and it ignores any information given by the entire sequence of observations. Thus, it becomes relatively insensitive to detecting weak items if the degradation path of the product degrades very slowly. To remedy this weakness, similar to the CUSUM control charting scheme in statistical process control, we propose an integrated Wiener process to model the cumulative degradation path of the product's quality characteristic. Then the optimal burn-in policy can be easily obtained. In addition, we also use an analytic approach to compare the efficiency of our proposed procedure with the method that is previously reported in the literature.     

Dispersion measurements of water with white-light interferometry

We measure the second- and third-order dispersion coefficients, d(2)k/domega(2) and d(3)k/domega(3), of water for wavelengths from 0.45 to 1.3 mum using a Michelson white-light interferometer. In this interval, the second-order dispersion ranges from 0.068 to -0.1 fs(2)/mum, and the third-order dispersion ranges from 0.048 to 1.18 fs(3)/mum. We observe an oscillation in d(2)k/domega(2) near 1.1 mum that is due to water absorption features near that wavelength. From the dispersion coefficients, derivatives of the index of refraction of water are calculated and compared with available equations. These measured values of d(2)n/dlambda(2) and d(3)n/dlambda(3) should be useful in the evaluation and improvement of existing equations for n(lambda) in water.     

Adaptive noise filtering using an error-backpropagation neuralnetwork

A neural network of the feedforward-error backpropagation type proposed by D.E. Rumelhart et al. (1986) was applied to filter noise from spectral data commonly encountered in infrared absorption of molecular transitions. The purpose was to gain insight into the way a neural network can be trained to remove noise from a noise-corrupted signal with implications for signal processing in general. The neural network simulation was implemented in Fortran and run on a VAX 8800. Training of the neural network occurred on a set of spectral data with random transitions and line shape parameters. Preliminary results of the performance of the adopted neural network are reported and discussed along with observed limitations. Future improvements on noise filtering using a neural network are proposed     

Measurement of strain concentration factor of composites plate using moiré interferometry

In this paper, using a 1200 lines/mm replicated grating, the moiré interferometry method was applied to study the strain concentration factor of a carbon fibre composites plate with a central hole. The rules of strain concentration factors were determined under different loads.     

Measurement of air turbulence for on-machine interferometry

There is increasing demand for in situ shape measurements performed on ultraprecision processing machines. One major source of error during interferometric measurements performed on machines is fringe displacement due to external disturbances. We have developed an interferometer equipped with an electro-optic phase modulator that measures the phase of interference fringes before they are displaced by air turbulence. The frequency characteristics of air turbulence induced by a heat source are derived from successive measurements of a test surface. Experimental results show that the phase of the interference fringes can be accurately measured in the presence of air turbulence when the intensity of the fringes is sampled at a speed of several hundred hertz.     

Removing spurious signals from glow curves using an optimal Wiener filter

During readout, the signal of the TLD is occasionally polluted with spurious signals. These most often take the shape of a spike on the glow curve. Often these spikes are only a few milliseconds wide but can have a height that significantly influences the outcome of the dose evaluation. The detection of spikes relies generally on comparing the raw glow curve with a smoothed version of it. A spike is detected when the height of the glow curve exceeds that of the smoothed curve, using criteria based on the absolute and relative differences. The procedure proposed is based on smoothing by an optimal Wiener filter, which is, on its turn, based on Fourier analysis for which numerically very efficient methods are available. Apart from having easy to understand tuning parameters, an attractive bonus is that, with only little additional computational effort, estimates of the position of peak maxima are found from second and third derivatives: a useful feature for glow curve quality control.     

Characterization of air entraining admixtures in concrete using surface tension measurements

Air entraining admixtures (AEA) are generally used for increasing the workability and resistance to freezing and thawing in concrete. These admixtures generate air bubbles with diameters ranging from 10 μm to 1 mm, providing spaces for the expansion of ice, and therefore facilitate frost protection. In this study, performances of AEAs were investigated based on surface tension measurements, accounting for the effect of AEAs on surface tension. For this purpose, a new test method was developed which depends on surface tension measurements according to the Du Nouy ring method. All types of AEAs used in the scope of this research presented a substantial influence on the surface tension. It was observed that a significant relationship between the air void system and surface tension exists. The surface tension method was found as a useful tool to determine the AEA type and content to obtain the desired air void system in concrete.     

Accurate velocity measurements of AFM-cantilever vibrations by Doppler interferometry

Doppler velocimetry is widely used in the measurement of nanometre resonance vibrations of micro-electromechanical systems (MEMS). It has excellent sensitivity and precision, but typical engineering applications do not require traceability of these velocity measurements to the SI system. While Doppler velocimetry is, in principle, easy to make traceable to the velocity of light, in practice a frequency-to-voltage conversion in common commercial instruments breaks this traceability unless calibrated. Typically, though, calibration is performed at a much lower frequency than those typical of MEMS devices, without the guarantee that the calibration is applicable in this higher frequency regime.

We present a method of traceable measurement of velocity in terms of the velocity of light, valid for the range of frequency and nanometre amplitudes typical of MEMS devices driven to resonance vibration. This is achieved by analysis of sideband amplitudes in the interference spectrum before demodulation of the Doppler signal. These sideband amplitudes can conveniently be measured using a benchtop spectrum analyser, a piece of widely available electrical test equipment. We illustrate the method with measurements on individual AFM cantilevers. In combination with cantilever calibration methods based on MEMS devices this method enables traceable calibration of those cantilevers employed for the measurement of pico- and nanonewton forces between individual biomolecules.     

Transport of vacuum arc plasma through an off-plane double bend filtering duct

A new magnetic macroparticle filter design consisting of an off-plane double-bend (OPDB) filter is described. The transport of the vacuum arc plasma through this OPDB filter is investigated using Langmuir and deposition probes. Films of amorphous hard carbon have been deposited using a 90° single bend and the OPDB filter and the macroparticle contents of the films are compared. The experimental results were found to be in good agreement with the simulations results based on an improved drift approximation model. The results demonstrate that OPDB filter has a relatively better transmission efficiency than the 90° single bend filter, lower macroparticle counts and is suitable for preparation of diamond-like carbon coatings with high quality.     

An experimental study of transpiration and combination cooling with turbulent flow of air through a round tube

We present the results from an experimental investigation into transpiration and combination cooling in the turbulent flow of air through a round tube; in addition, we present the empirical relationships derived on the basis of experimental data.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 16, No. 3, pp. 417–422, Marcy, 1969.     

Friction drag of turbulent finely dispersed air mixtures

On the basis of a theoretical analysis of the turbulent stresses due to momentum transfer the author determines the excess drag coefficient in a finely dispersed air-mixture flow. The results obtained are checked against the experimental data.     

Propagation of a partially coherent beam from an unstable resonator through turbulent atmosphere

The influence of atmospheric turbulence on the propagation of a partially coherent beam from an unstable resonator was studied numerically. The resonant mode of the unstable resonator is obtained by iterative calculation using the Huygens–Fresnel formula. Also, using the extended Huygens–Fresnel integral, the intensity distribution of a propagating laser beam is calculated for different conditions. The influence of turbulence on the profile of partially coherent beams of an unstable resonator is studied. The effects of geometrical parameters of the resonator on the far-field beam profile are investigated. The results show that an unstable resonator with higher magnification has a superior far-field beam profile under partial coherency and turbulence conditions.