High resolution processing techniques for ultrasound doppler velocimetry in the presence of colored noise. Part I: Nonstationary methods

Real-time flow velocity measurement is a practical issue in industrial and biomedical applications. Because their good frequency resolution, parametric methods such as autoregressive (AR) modeling and time-frequency distributions (TFD) are generally preferred to Fourier analysis. However, these methods become highly inaccurate in the presence of colored noise. We review here the principal parametric and nonparametric techniques and show their limitations in the estimation of Doppler frequency in the presence of strong colored noise. Different solutions to overcome these limitations are then proposed and compared using synthetic Doppler signals with colored noise.     

Microstructural effects on properties and new processing techniques of Silicon Nitride. Part II: New processing techniques of silicon nitride

In part I of this paper the relationship between microstructure and various mechanical, thermal and thermo-mechanical properties of hot-pressed and reaction-bonded silicon nitride, such as fracture strength, thermal diffusivity and thermal shock resistance, was discussed. On the basis of this correlation today's limits of silicon nitride regarding a broader application and the possibilities for optimizing this material group were outlined. This discussion demonstrates the necessity of further improving some important properties and of developing new processing techniques. In part II the development lines of these new techniques for silicon nitride processing are discussed and a survey is given of recent progresses in the use of those techniques. As an example of a new processing technique, results of hot-isostatic pressing of reaction-bonded silicon nitride are presented in more detail.     

Strategies for enhancing noise immunity in measurement of the average frequency of secondary doppler signals

We analyze algorithms for measurement of the average frequency of the secondary Doppler signal which possess much higher noise immunity than the traditional maximum likelihood method.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 25–29, June, 1995.     

Correlation measurement of the velocity of ultrasound in sheet materials

Conclusions The newly developed correlation method makes it possible to measure the velocity of ultrasound in moving flexible sheet materials in the presence of intense acoustic noise. A high measurement accuracy is achieved through the use of a noisy ultrasonic signal with a large base length. The method is practical for continuous testing of the mechanical properties of sheet materials under industrial conditions.Translated from Izmeritel'naya Tekhnika, Vol. 19, No. 6, pp. 88–90, June, 1976.     

Reconstructing the parameters of geofields taking measurement noise into account. Part II. Techniques for identification,regularization, and soft computing

Various methods for reconstructing the parameters of geofields taking measurement noise into account are analyzed. Program packages for nonspecialists in the theory of programming are discussed. Recommendations are given regarding the correct choice of method and control parameters for approximating and modelling geofields. The advantages and disadvantages of these methods in different stages of the recovery of the parameters of geofields are examined. It is proposed that fuzzy neural networks be utilized in the early stage when the data are uncertain and limited.     

A novel beamformer design method for medical ultrasound. Part II: Simulation results

For pt.I see ibid., vol.50, no.1, p.15 (2003). In the first part of this work, we introduced the minimum sum squared error (MSSE) technique of ultrasound beamformer design. This technique enables the optimal design of apertures to achieve arbitrary system responses. In the MSSE technique, aperture weights are calculated and applied to minimize the sum squared error (SSE) between the desired and actual system responses. In this paper, we present the results of simulations performed to illustrate the implementation and validity of the MSSE technique. Continuous wave (CW) and broadband simulations are presented to demonstrate the application of the MSSE method to obtain arbitrary system responses (within fundamental physical limitations of the system). We also describe CW and broadband simulations that implement the MSSE method for improved conventional depth of field (DOF) and for improved correlation DOF in translated aperture geometries. Using the MSSE technique, we improved the conventional DOF by more than 200% in CW simulations and more than 100% in broadband simulations. The correlation DOF in translated aperture geometries was improved by more than 700% in both CW and broadband simulations.     

Use of modulated excitation signals in medical ultrasound. Part II: Design and performance for medical imaging applications

In the first paper, the superiority of linear FM signals was shown in terms of signal-to-noise ratio and robustness to tissue attenuation. This second paper in the series of three papers on the application of coded excitation signals in medical ultrasound presents design methods of linear FM signals and mismatched filters, in order to meet the higher demands on resolution in ultrasound imaging. It is shown that for the small time-bandwidth (TB) products available in ultrasound, the rectangular spectrum approximation is not valid, which reduces the effectiveness of weighting. Additionally, the distant range sidelobes are associated with the ripples of the spectrum amplitude and, thus, cannot be removed by weighting. Ripple reduction is achieved through amplitude or phase predistortion of the transmitted signals. Mismatched filters are designed to efficiently use the available bandwidth and at the same time to be insensitive to the transducer's impulse response. With these techniques, temporal sidelobes are kept below 60 to 100 dB, image contrast is improved by reducing the energy within the sidelobe region, and axial resolution is preserved. The method is evaluated first for resolution performance and axial sidelobes through simulations with the program Field II. A coded excitation ultrasound imaging system based on a commercial scanner and a 4 MHz probe driven by coded sequences is presented and used for the clinical evaluation of the coded excitation/compression scheme. The clinical images show a significant improvement in penetration depth and contrast, while they preserve both axial and lateral resolution. At the maximum acquisition depth of 15 cm, there is an improvement of more than 10 dB in the signal-to-noise ratio of the images. The paper also presents acquired images, using complementary Golay codes, that show the deleterious effects of attenuation on binary codes when processed with a matched filter, also confirmed by presented simulated images.     

Use of modulated excitation signals in medical ultrasound. Part III: High frame rate imaging

This paper, the last from a series of three papers on the application of coded excitation signals in medical ultrasound, investigates the possibility of increasing the frame rate in ultrasound imaging by using modulated excitation signals. Linear array-coded imaging and sparse synthetic transmit aperture imaging are considered, and the trade-offs between frame rate, image quality, and SNR are discussed. It is shown that FM codes can be used to increase the frame rate by a factor of two without a degradation in image quality and by a factor of 5, if a slight decrease in image quality can be accepted. The use of synthetic transmit aperture imaging is also considered, and it is here shown that Hadamard spatial encoding in transmit with FM emission signals can be used to increase the frame rate by 12 to 25 times with either a slight or no reduction in signal-to-noise ratio and image quality. By using these techniques a complete ultrasound-phased array image can be created using only two emissions.     

Reconstructing the parameters of geofields taking measurement noise into account. Part I. Techniques for smoothing,filtration, and regularization

Various methods of interpolation (approximation, smoothing, and filtering types) which take measurement noise into account (piecewise polynomial approximation, smoothing splines, kriging, filters, etc.) are analyzed. It is found that regularization methods are used in all of them. The advantages and disadvantages of these methods are pointed out and prospects for the use of program packages by nonspecialists in mathematics and information technology are examined. Recommendations regarding the proper choice of estimation techniques, quality criteria, and parameters for monitoring them are made in the case where geofields are to be approximated and modelled.     

Methodological approaches for histamine quantification using derivatization by chloroethylnitrosourea and ELISA measurement. Part II: Optimisation of the derivatization step

In a previous paper (part I), new strategy was used for raising antibodies against hapten (< 300 Da) and the quantification of these hapten by ELISA using derivatization by chloroethyl nitrosourea (CENU). After raising antibodies against histamine, they were characterized and used for ELISA measurements. Optimal detection conditions were determined for the histamine quantification by ELISA method. The present study investigates the derivatization step of the histamine by chloroethylnitrosourea (CENU). Five factors (2 qualitative: nature of the solvent and nature of the antibodies and 3 quantitative: pH, % of solvent and time of derivatization) have been considered. Optimal reaction conditions were established by calculation of a validated model.     

Synthesis of carbon nanotube films by thermal CVD in the presence of supported catalyst particles. Part II: the nanotube film

Carbon nanotube films have been grown at 750° and 900 °C by thermal chemical vapor deposition (CVD) with acetylene (C₂H₂) and hydrogen on silicon (0 0 2) wafers supporting preformed (Fe,Si)₃O₄ particles. The reduction of the (Fe,Si)₃O₄ particles during CVD at 750 °C was accompanied by a disintegration leading to the formation of a high density of smaller (predominantly 5–15 nm) iron silicide (₁-Fe₂Si) particles that catalyzed the growth of a dense and aligned multi-wall carbon nanotube film. The tubes did not contain any inclusions apart from the catalytic particles present in the bottom part of the film, and it was concluded that the nanotubes grew via a base-growth mechanism. CVD at 900 °C resulted in a random growth of predominantly multi-wall carbon nanotubes. The film contained an increased number of amorphous carbon, or graphite, clusters containing particles that had been carbonized, the larger ones to cementite, -Fe₃C. Nanotubes were observed to grow from some of these clusters. Multi-wall carbon nanotube tips contained after CVD at 900 °C encapsulated -Fe₃C, or in a few cases - or -Fe, particles.     

Effect of composition and processing parameters on the characteristics of tannin-based rigid foams. Part II: Physical properties

The present work is the continuation of the previous one published in the same issue of this journal, but now focuses on some selected physical properties of tannin-based rigid foams and derived glasslike carbon foams. Such materials are new, lightweight, cellular solids, prepared from 95% natural precursors: bark extracts and furfuryl alcohol, as detailed in the companion paper. After a few structural characteristics are briefly recalled, physical properties like compressive strength, permeability to fluids, solvent absorption, and electrical conductivity are measured, discussed and modelled. The effects of changing a few experimental parameters that have been varied in the synthesis of the foam: amounts of blowing agent, strengthener and nanofillers, shape of the moulds and restricted foaming are discussed in relation with the pore structure observed in the companion paper. Slightly anisotropic properties are evidenced, in agreement with the orientation of the cells, as expected for foams grown vertically in cylindrical moulds.     

Optical beating of polychromatic light and its impact on time-resolved spectroscopy. Part II: Strategies for spectroscopic sensing in the presence of optical beating

Time-resolved spectroscopy can be compromised by optical beating, which is inherent to polychromatic light sources and signals. For incoherent light sources, the random interference can partially or completely mask the spectroscopic signature of interest if the time dynamics of the interference are similar to or faster than that of the signature. Part I of this review focused on the theory of this process with an emphasis on thermal light sources, and in this part, four methods to mitigate or circumnavigate the detrimental impact of interference on time-resolved spectroscopy are reviewed: use of light with a controlled, non-stochastic phase, use of narrow-bandwidth light, averaging, and pulse referencing.     

Maximum likelihood for target location in the presence of substitutive noise

We consider the optimal likelihood algorithm for the estimation of a target location when the images are corrupted by substitutive noise. We show the relationship between the optimal algorithm and the sliced orthogonal nonlinear generalized (SONG) correlation. The SONG correlation is based on the application of a linear correlation to corresponding binary slices of both the input scene and the reference object with appropriate weight factors. For a particular case, we show that the optimal strategy is a function of only the number of pixels for which the gray values in the noisy image match the ones of the reference image when the substitutive noise is uniformly distributed. This is exactly what a particular definition of the SONG correlation does.     

Image recognition in the presence of non-Gaussian noise with unknown statistics.

We design receivers to detect a known pattern or a reference signal in the presence of very general and non-Gaussian types of noise. Three sources of input-noise degradation are considered: additive, multiplicative, and disjoint background. The detection process involves two steps: (1) estimation of the relevant noise parameters within the framework of hypothesis testing and (2) maximizing a certain metric that measures the likelihood of the target being at a given location. The parameter estimation portion is carried out by moment-matching techniques. Because of the number of unknown parameters and the fact that various types of input-noise processes are non-Gaussian, the methods that are used to estimate these parameters differ from the standard methods of maximizing the likelihood function. To verify the existence of the target at a certain location, we use l(p)-norm metric for p > or = 0 to measure the likelihood of the target being present at the location of interest. Computer simulations are used to show that for the images tested here, the receivers designed herein perform better than some existing receivers.     

He II常流体粘度实验测量技术研究进展

目前还没有现成的理论可以对He II粘度进行合理的说明和计算,在大多数情况下还只能依靠实验技术来满足其工程需要。本文对传统实验技术,目前出现的各种改进型实验技术进行了概述,事实表明不同的实验技术所得的结果之间偶有符合,但不能从根本上解决He II粘度对实验技术的依赖性,目前的实验技术还无法提供He II粘度数值的一致性结论。但是通过对He II粘度与温度之间的变化趋势、数值的数量级等方面的分析,证明了He II粘度在1.6 K~1.8 K之间形成了最小值区域。当温度继续低于1.6 K时,He II粘度会迅速增加,同样在温度高于1.8 K时,随着温度的增加,He II粘度也会迅速增加。     

Multiscale Computations of Parameters of Power Transformer Windings at High Frequencies. Part II: Large-Scale Level

In this part of the paper, we focus on implementation of a hierarchical multiscale approach for modeling high-frequency electromagnetic processes in power transformers. We present a large-scale 3D computer model for calculating magnetic fields in a transformer and evaluating effective parameters (inductance and resistance) of its windings and losses. The model accounts for complex, anisotropic, and frequency-dependent effective diamagnetic properties of the windings, which are obtained by solving small-scale 2D field problems as described in Part I of the paper. Results of the computations performed for a test transformer are analyzed in the frequency range 10 Hz-10 MHz. We discuss effects of windings conditions (open and short-circuited) and their location on the transformer core.     

Optimal transformations for optical multiplex measurements in the presence of photon noise

Hadamard multiplexing is a measurement strategy that yields best sensitivity improvements over scanning measurements for signal-independent detector noise. The presence of photon noise degrades the performance of Hadamard multiplexing because of the increase of photon noise by the superposition of multiple signals. I derive the reduction of the sensitivity gain of a Hadamard measurement and an upper limit for the gain of any cyclic multiplexing strategy in the presence of photon noise. This upper limit clearly exceeds the reduced Hadamard gain and can be achieved by multiplexing sequences that differ from Hadamard S sequences but also share some similarities with respect to their autocorrelation. Examples of such sequences are given. As the analysis shows, the presence of photon noise limits the gain of multiplexing strategies to a finite value, which depends on the ratio between photon noise and detector noise and cannot be exceeded by increasing the number of multiplexed channels. In addition, only switching multiplex schemes, which superpose either all the light or no light of individual channels, can achieve the upper limit of the gain.     

Image preprocessing for rotation-invariant pattern recognition in the presence of signal-dependent noise

I propose a new method that ensures efficient rotation-invariant pattern recognition in the presence of signal-dependent noise by combining the application of rotation-invariant correlation filters with preprocessing of the noisy input images. The preprocessing uses local suboptimal estimators derived from estimation theory and implies an a priori knowledge of a model describing the noise source. The image noise sources considered are speckle and film-grain noise. Pour different metrics are used to analyze the correlation performance of the circular-harmonic filter, the phase-only circular-harmonic filter, and the binary phase-only circular-harmonic filter, with and without a preprocessing. Computer simulations show that signal-dependent noise can seriously degrade the performance of the phase-only circular-harmonic filter and the binary phase-only circular-harmonic filter. The most severe indication of correlation-performance degradation is the occurrence of false alarms in 15% to 20% of noise realizations of the correlation. Preprocessing increases the correlation-peak signal-to-noise ratio significantly and reduces the false-alarm probability by one to two orders of magnitude.