Spectral analysis of Doppler ultrasonic decompression data

Several aspects of spectral analysis of bubble transients in Doppler ultrasonic decompression data are discussed. The computation of energy density spectra, using fast Fourier transform techniques for analyzing bubble transients, is described. Spectral analysis of data from probes implanted within animals, using a conventional Fourier analyzer, provided good visual indications of bubble events and interesting changes in spectral structure. A new transient spectral analysis technique that is suitable for quantitative real-time monitoring of small decompression bubbles is described. In a feasibility study using data from an implanted probe, an increase of 900% in bubble signal/noise ratio was observed.     

微型化多通道滤光片光谱串扰模型的建立和评价

多光谱成像可以从背景中凸显出目标物,但微型多通道滤光片在不同通道之间存在光谱串扰问题,影响目标的识别。通过光谱串扰分析,建立光谱串扰模型,提出光谱串扰系数,通过灰度值统计的方法定量评价光谱串扰。对已加工的一种光谱串扰程度约为16.74%的微型多通道滤光片获取的多光谱图像进行了对比分析,经过串扰模型处理后的图像与原始图像相比,其对比度有了显著的提高。实验分析结果表明,该模型对评价多通道微型多光谱滤光片的光谱串扰具有很强的针对性,对提高多光谱图像目标识别效果明显。     

The analysis of data obtained with time to amplitude converter and multichannel analyser systems

An exact general formula is derived relating the data obtained from t.a.c-m.c.a. systems to the input signal distribution; it is shown how the latter is modified by the measuring process. A general method of data correction is given, together with important approximations, which evaluates the input signal distribution from the data without any loss of signal. A simple and accurate method of system calibration based only on counting and not requiring the use of calibrated delay lines is also given. Paper G6 presented at 3rd Internat'l Conf. Positron Annihilation, Otaniemi, Finland (August 1973).     

An ESPI apparatus with multichannel data acquisition

An ESPI (Electronic Speckle Pattern Interferometry) apparatus employing a linear photodiodes array for multichannel data acquisition is described. The technique is applied for measurements of normal displacements of surfaces when time and space resolutions are required.     

Improved Lanczos algorithms for blackbox MRS data quantitation

Magnetic resonance spectroscopy (MRS) has been shown to be a potentially important medical diagnostic tool. The success of MRS depends on the quantitative data analysis, i.e., the interpretation of the signal in terms of relevant physical parameters, such as frequencies, decay constants, and amplitudes. A variety of time-domain algorithms to extract parameters have been developed. On the one hand, there are so-called blackbox methods. Minimal user interaction and limited incorporation of prior knowledge are inherent to this type of method. On the other hand, interactive methods exist that are iterative, require user involvement, and allow inclusion of prior knowledge. We focus on blackbox methods. The computationally most intensive part of these blackbox methods is the computation of the singular value decomposition (SVD) of a Hankel matrix. Our goal is to reduce the needed computational time without affecting the accuracy of the parameters of interest. To this end, algorithms based on the Lanczos method are suitable because the main computation at each step, a matrix-vector product, can be efficiently performed by means of the fast Fourier transform exploiting the structure of the involved matrix. We compare the performance in terms of accuracy and efficiency of four algorithms: the classical SVD algorithm based on the QR decomposition, the Lanczos algorithm, the Lanczos algorithm with partial reorthogonalization, and the implicitly restarted Lanczos algorithm. Extensive simulation studies show that the latter two algorithms perform best.     

Subspace-based MRS data quantitation of multiplets using prior knowledge

Accurate quantitation of Magnetic Resonance Spectroscopy (MRS) signals is an essential step before converting the estimated signal parameters, such as frequencies, damping factors, and amplitudes, into biochemical quantities (concentration, pH). Several subspace-based parameter estimators have been developed for this task, which are efficient and accurate time-domain algorithms. However, they suffer from a serious drawback: they allow only a limited inclusion of prior knowledge which is important for accuracy and resolution. In this paper, a new method is presented: KNOB-SVD and its improved variant KNOB-TLS. KNOB-SVD is a recently proposed method, based on the Singular Value Decomposition (SVD), which allows the use of more prior knowledge about the signal parameters than previously published subspace-based methods. We compare its performance in terms of robustness and accuracy with the performance of three commonly used methods for signal parameter estimation: HTLS, a subspace-based method which does not allow any inclusion of prior knowledge, except for the model order; HTLSPK(Delta fd(eq)), a subspace-based method obtained by incorporating in HTLS the prior information that the frequency differences between doublet components are known and the damping factors are equal; and AMARES, an interactive maximum likelihood method that allows the inclusion of a variety of prior knowledge. Extensive simulation and in vivo studies, using (31)P as well as proton MRS signals, show that the new method outperforms HTLS and HTLSPK(Delta fd(eq)) in robustness, accuracy, and resolution, and that it provides parameter estimates comparable to the AMARES ones.     

New data processing for multichannel FIR laser interferometer

Usually, both the probing and reference signals received by LATGS detectors of FIR interferometer pass through hardware phase discriminator and the output phase difference--hence the electron line densities is collected for analysis and display with a computerized data acquisition system(DAS). In this paper, a new numerical method for computing the phase difference in software has been developed instead of hardware phase discriminator, the temporal resolution and stability is improved. An asymmetrical Abel inversion is applied to processing the data from a seven-channel FIR HCN laser interferometer and the space-time distributions of plasma electron density in the HT-6M tokamak are derived.     

在摄像式塞曼效应实验装置上实现光学多道方式光谱测量

在采用CCD摄像方式的微机塞曼效应实验装置上,不改变原有硬件,只利用计算机技术编制程序,将在干涉环图像上用画圆方式测量数据的方法转换为用光学多道方法来测量数据,完善了数据的测量方法,提高了实验装置的性能.     

On the use of multichannel data acquisition of impedance spectra

Impedance spectroscopy is a powerful technique for electrical and electrochemical characterisation of ionic conductors and other electroceramics. Thus, one might tempted to use multichannel data acquisition to allow the utilisation of expensive LCR meters for simultaneous measurements. This work shows results for YSZ and strontium titanate ceramics, obtained with a multi-channel data acquisition system, to demonstrate the limitations of this approach and the applicability of some corrections. Impedance spectra are affected under multi-channel conditions, mainly in the high frequency contributions, and this is approximately described by a stray capacitance. The bulk contribution of the spectra is most affected. Contributions of internal interfaces (e.g. grain boundaries) are relatively well characterised, mainly after the proposed corrections. The characterisation of electrode processes is not affected. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002.     

Effect of locking of photon echo signals in multichannel data recording

The effect of locking of a long-lived photon echo is investigated in the case where nonresonant laser radiation (a standing or traveling wave with an artificially created spatial inhomogeneity) serves as an inhomogeneous external perturbation, which results in random shifts or splitting of the initial monochromatic components of the inhomogeneously broadened line. The use of the mutual spatial orientation of the gradients of electric fields as an associative key of access to recorded information allows one to produce a large number of independent channels of data recording. It is demonstrated that the proposed scheme for recording and associative sampling of information has the advantage that, in each channel, information is recorded simultaneously at all optical centers (the whole inhomogeneously broadened resonance line), which does not decrease the intensity of the response from each channel. Moreover, the echo holographic information coded in the wavefronts of the exciting pulses can also be recorded in each channel, which does not affect the independence of individual channels of data recording.     

Spectral analysis informs the proper frequency in the sampling of financial time series data

Applied econometricians tend to show a long neglect for the proper frequency to be considered while sampling the time series data. The present study shows how spectral analysis can be usefully employed to fix this problem. The case is illustrated with ultra-high-frequency data and daily prices of four selected stocks listed on the Sao Paulo stock exchange.     

Spectral and energetic characteristics of passing vibrationally excited SF6 molecules through a cooled multichannel plate

We study the spectral and energetic characteristics of SF₆ molecules excited in a pulsed molecular beam by intense IR laser radiation into high-lying vibrational states (with the energy E _v ≥ 0.3–2.0 eV) that pass through a multichannel metal plate that is cooled to T _s ? 80–85 K and is inclined to the beam axis. From comparison of the measured characteristics with the spectral and energetic characteristics of the IR multiphoton absorption of these molecules, we find that they correlate rather well with each other. The results obtained allow us to conclude that, due to different probabilities of passing vibrationally excited and unexcited molecules through the multichannel plate, it is possible to separate molecules in the beam with respect to their isotopic (component) composition.     

Spectral analysis of uranium glasses

A Taylor-series expansion of the intermediate coupling energy levels for the U⁴⁺(5f²) has been developed for the first time by using the mathematical procedures of Racah. The partial derivatives, eigenvalues and eigenfunctions reported in this paper will be of great use in analysing the optical spectral properties of the tetravalent uranium doped crystalline or non-crystalline materials. The usefulness of the Taylor serier expansion has been verified by examining the optical absorption results of the U⁴⁺ doped fluoride glasses. The physical properties, namely the refractive index and density, were also determined.Our thanks are due to Prof. S. V. J. Lakshman for his kind cooperation and support in the present work. We are also thankful to the technical staff of the Hull University, Physics Department, UK in the preparation and measurement of various physical properties of the U⁴⁺ doped alkali mixed heavy metal based fluoride glass systems.     

Spectral deconvolution of NMR cross polarization data sets

The COmponent-REsolved (CORE) strategy has been employed, for the first time to solid state NMR spectroscopy. CORE was used to extract two time-dependent spectral components in 24 ²⁹Si{¹H} NMR spectra, recorded on a meso-structured silica material under conditions of cross polarization evolution. No prior assumptions were made about the component bandshapes, which were both found to be skewed to higher chemical shifts. For the silica fragments close to protons this skewness could be rationalized by a distribution of the degree of condensation in the silica network; however, for the other component the non-Gaussian shape was unexpected. We expect that the same strategy could be applied to a range of experiments in solid-state NMR spectroscopy, where spectral distributions or kinetic parameters need to be accurately extracted.     

Properties of baryon resonances from a multichannel partial wave analysis

Properties of nucleon and Δ resonances are derived from a multichannel partial wave analysis of pion and photo-induced reactions off protons. This paper summarizes the latest results on masses, widths, and decay properties of nucleon and Δ resonances.