Estimation of the in vivo decay rate of EPR signals for a nitroxide radical in rat brains by a region-selected intensity determination method

The region-selected intensity determination (RSID) method was proposed to obtain the temporal changes in electron paramagnetic resonance (EPR) signal intensity from a selected region by a stationary magnetic field gradient. To select the region, the subtraction field that was derived from the distance between the center and the projection of the selected region to the direction of the field gradient was applied to the main field. The directions of the stationary magnetic field gradient at a constant strength were systematically changed in a three-dimensional space after each acquisition of the spectrum. All spectra under the field gradient were accumulated and the resultant spectrum was deconvoluted by a spectrum without the field gradient. The center height of the deconvoluted spectrum indicates the signal intensity of the selected region. To verify this method, a phantom or in vivo study was conducted on a 700 MHz radio-frequency EPR spectrometer equipped with a bridged loop-gap resonator. In the temporal EPR measurements of phantoms including a nitroxide radical aqueous solution with and without ascorbic acid, the selected regions were alternatively changed at the position of the two phantoms. The signal intensity derived from the one phantom showed an exponential decay, and for the other phantom, no temporal changes. The spatial resolution of this method was estimated to be 2.7 mm by using a pinpoint phantom that included diphenylpicrylhydrazyl powder. In the in vivo temporal EPR measurements, the selected regions were alternatively changed at the cerebral cortex and the striatum of rats that had received a blood-brain barrier-permeative nitroxide radical. The decay rate of the signal intensity at each region obtained by this method was consistent with those previously reported.     

固定干扰源存在下的管道泄漏检测和准确定位

为了解决固定位置的声/振动干扰源引起的管道泄漏声检测的虚警或者漏点定位错误问题,利用泄漏信号源和固定干扰源之间的独立性,通过盲卷源分离算法得到泄漏信号在一定代价函数下的最优估计,并将该估计作为输入信号从检测信号中自适应预测得到泄漏信号,这样就可以保留泄漏信号中的时延信息。对实际检测信号的处理表明,应用提出来的方法可以有效的去除检测信号中来自固定干扰源的噪声,同时不损失泄漏信号中的时延信息,可在固定干扰源存在时实现管道泄漏有效检测和准确定位。      

CCD成像系统信号处理过程的软件仿真与参数优化

对CCD成像系统的AGC(Automatic Gain Control)、背光补偿、伽玛校正等信号处理过程进行了理论分析,在此基础上,讨论了CCD成像系统信号处理过程的仿真与参数优化方法,编写了相关仿真软件。实验结果表明:所讨论的方法能够实现CCD成像系统信号处理过程的软件仿真,并同时实现相关控制参数的优化。     

随机共振法估计二水听器时延差

针对二元阵航船目标方位估计问题,提出了一种基于随机共振滤波的航船辐射噪声双水听器时延差估计方法。设计了一种随机共振滤波器,提取航船螺旋桨旋转噪声在水听器接收信号中出现的本地时间,并通过滤波结果的互相关来估计目标辐射噪声分别到达两个水听器的时延差。在5 dB的输入信噪比下进行200次仿真,提出方法时延估计的归一化均方误差要低于互谱方法一个数量级。对于海试中的非合作航船,提出的方法可以在1 km距离下准确估计出目标辐射噪声到达双水听器的时延差,从而为在二元阵上实现对航船目标的准确测向提供基础。      

Absolute determination of the X‐ray absorption coefficient of barium in the L region using a liquid absorption cell

A method of absolute measurement of X‐ray absorption coefficient is proposed, on the basis of the use of an adjustable pathlength liquid cell and a solution of the investigated element. A variational analysis of the measured data is developed to remove some sources of systematic error. A check of the exponential attenuation with thickness is used to suppress beam harmonics admixture and dark current drifts. The method is illustrated by a measurement on Ba in the L edge region, using aqueous solution of Ba nitrate. Measured data provide information on detailed energy dependence of the absorption beyond the Victoreen‐like trends reproduced in compilations. The proposed method provides a way to measure the absorption data for practically all elements and a wide range of photon energies. Copyright © 2012 John Wiley & Sons, Ltd.     

聚甲基丙烯酸甲酯间隔的金纳米立方体与金膜复合结构的表面增强拉曼散射研究

金属纳米颗粒与金属薄膜的复合结构由于其局域表面等离子体和传播表面等离子体间的强共振耦合作用,可作为表面增强拉曼散射(SERS)基底,显著增强吸附分子的拉曼信号.本文提出了一种聚甲基丙烯酸甲酯(PMMA)间隔的90 nm金纳米立方体与50 nm金膜复合结构的SERS基底,通过有限元方法数值模拟,得到PMMA的最优化厚度为15 nm.实验制备了PMMA间隔层厚度为14 nm的复合结构,利用罗丹明6G (R6G)为拉曼探针分子, 633 nm的氦氖激光器作为激发光源,研究了复合结构和单一金纳米立方体的SERS效应,发现复合结构可以使探针分子产生比单一结构更强的拉曼信号.在此基础上,研究了不同浓度金纳米立方体水溶液条件下复合结构中R6G的拉曼光谱.结果表明,当金纳米立方体水溶液浓度为5.625μg/mL的条件下复合结构中R6G的拉曼信号最强,且可测量R6G的最低浓度达10~(–11) mol/L.     

Retrieval of the quasi-optimal signal activating the excitable systems using preceding noise samples

We propose a method for obtaining a signal leading to the activation of an excitable dynamic system for a signal energy close to minimal. The efficiency of this technique, which is based on recording and processing of noise samples preceding the activation was tested using the FitzHugh–Nagumo, Hodgkin–Huxley, and Luo–Rudy models as examples. It is shown that the proposed procedure gives good results when the noise intensity is smaller than or close to the system activation energy. The criteria of “low” and “high” intensities of fluctuations are proposed. The method of increasing the stability of the excitable system with respect to “low-intensity” noise by filtering or another way of suppression of the spectral components that make the main contribution to the energetically optimal activation signal is justified. The relation between eigenvalues of the linearized system of the Hamiltonian equations, which describe the optimal trajectories and the activation signal, and eigenvalues of the excitable system linearized near the initial equilibroum state is found.     

Signal processing for radiation dosimetry using EPR in dental enamel: comparison of three methods

We are reporting an alternative method of extracting useful dose information from complex EPR spectra of dental enamel. Digital differentiation of the initial first derivative spectrum followed by filtering is used to clearly distinguish the radiation-induced signal from the native background signal. The peak-to-peak height of the resulting second derivative of the signal is then measured as an indication of absorbed dose. This method does not require preliminary elimination of the native background signal, and is not effected by any uncertainty in the determination of the background signal or by errors resulting from the subtraction of two signals of comparable magnitude. Ten enamel samples were irradiated with known doses in the range of 250–10⁵ mGy. There was agreement for all the samples, within the typical experimental error of ±10% for EPR dosimetry in dental enamel, between the doses determined by two common techniques using native signal subtraction and the doses determined by the new second derivative method proposed here.     

Measurement of the spin-lattice relaxation time in the NQR of light nuclei

This work proposed a method for increasing the signal/noise ratio in NQR by preliminary magnetization of the sample in a constant magnetic field B₀ and its subsequent adiabatic demagnetization. The proposed method for the measurement of spin-lattice relaxation times is verified experimentally with a number of compounds. The results agree well with published data.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 88–91, July, 1987.     

Three-dimensional visualization of objects in scattering medium using integral imaging and spectral analysis

This paper presents a three-dimensional visualization method of 3D objects in a scattering medium. The proposed method employs integral imaging and spectral analysis to improve the visual quality of 3D images. The images observed from 3D objects in the scattering medium such as turbid water suffer from image degradation due to scattering. The main reason is that the observed image signal is very weak compared with the scattering signal. Common image enhancement techniques including histogram equalization and contrast enhancement works improperly to overcome the problem. Thus, integral imaging that enables to integrate the weak signals from multiple images was discussed to improve image quality. In this paper, we apply spectral analysis to an integral imaging system such as the computational integral imaging reconstruction. Also, we introduce a signal model with a visibility parameter to analyze the scattering signal. The proposed method based on spectral analysis efficiently estimates the original signal and it is applied to elemental images. The visibility-enhanced elemental images are then used to reconstruct 3D images using a computational integral imaging reconstruction algorithm. To evaluate the proposed method, we perform the optical experiments for 3D objects in turbid water. The experimental results indicate that the proposed method outperforms the existing methods.     

一种消除测速模糊的梳状谱信号设计方法

相比于传统信号,梳状谱具有更好的混响抑制能力,但其容易产生多普勒测速模糊。为了解决这一问题,设计了一种新的几何梳状谱信号,通过分析测速模糊产生的原因,在传统频点计算方法的基础上,利用在信号频点计算中加入一组抗多普勒频率间隔的方法,以降低频点的重合。仿真分析证明,提出的梳状谱信号设计方法有效的减少了速度搜索时频谱重叠的程度,无论在噪声还是混响限制条件下均可以获得一个明显的输出峰值,避免了测速模糊的问题,可以获得比传统信号更好的检测性能。     

Chatter detection in band sawing based on discriminant analysis of sound features

In the paper chatter detection in band sawing is considered as a signal processing and classification problem. A multi-sensory experimental setup was established on an industrial band saw including sound, acceleration and cutting force, and measurements. Based on an experimental analysis sound signal is shown to be the most appropriate for chatter detection, therefore a sound-based online chatter detection method is proposed. The method consists of a sound signal pre-processing with Short-Time Fourier Transform, extraction of features in frequency space with optimal threshold and application of Quadratic Discriminant Analysis for chatter detection. The proposed method tested with twofold cross validation yields over 96% success of chatter detection.     

Statistical methods for detecting activated regions in functional MRI of the brain

Two statistical tests for detecting activated pixels in functional MRI (fMRI) data are presented. The first test (t-test) is the optimal solution to the problem of detecting a known activation signal in Gaussian white noise. The results of this test are shown to be equivalent to the cross-correlation method that is widely used for activation detection in fMRI. The second test (F test) is the optimal solution when the measured data are modeled to consist of an unknown activation signal that lies in a known lower dimensional subspace of the measurement space with added Gaussian white noise. A model for the signal subspace based on a truncated trigonometric Fourier series is proposed for periodic activation–baseline imaging paradigms. The advantage of the second method is that it does not assume any information about the shape or delay of the activation signal, except that it is periodic with the same period as the activation–baseline pattern. The two models are applied to experimental echo-planar fMRI data sets and the results are compared.     

Modeling the recorded spectrum and reconstructing the transfer function of the wideband ionospheric HF radio channel in the case of chirp sounding

We model theoretically the received spectrum in the case of sounding of the ionospheric HF radio channel by a chirp signal. It is shown that the result of processing of an individual time sample of the received signal is equivalent to the sounding of the radio channel by a complex narrow-band pulsed signal such that the group delays of its propagation modes determine the maxima in the received spectrum. We analyze the quadrature components of realizations of the received signal at the intermediate frequency at the bandpass-filter output in the receiving channel of the chirp ionosonde. The results of our analysis show the possibility of reconstructing the transfer function of a HF radio channel in the sounding-frequency band for the delay range determined by the characteristics of the intermediate-frequency bandpass filter. We propose a method for reconstructing the transfer function of the ionospheric radio channel, which involves supplementing the circuit of primary processing of the signal by a corrective digital filter with specified amplitude-frequency and phase-frequency characteristics. The proposed method can be used for all operating regimes of the chirp ionosonde in the case of digital recording and processing of signals. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 5, pp. 387–395, May 2007.     

Application of Generalized Composite Multiscale Lempel–Ziv Complexity in Identifying Wind Turbine Gearbox Faults

Wind turbine gearboxes operate in harsh environments; therefore, the resulting gear vibration signal has characteristics of strong nonlinearity, is non-stationary, and has a low signal-to-noise ratio, which indicates that it is difficult to identify wind turbine gearbox faults effectively by the traditional methods. To solve this problem, this paper proposes a new fault diagnosis method for wind turbine gearboxes based on generalized composite multiscale Lempel–Ziv complexity (GCMLZC). Within the proposed method, an effective technique named multiscale morphological-hat convolution operator (MHCO) is firstly presented to remove the noise interference information of the original gear vibration signal. Then, the GCMLZC of the filtered signal was calculated to extract gear fault features. Finally, the extracted fault features were input into softmax classifier for automatically identifying different health conditions of wind turbine gearboxes. The effectiveness of the proposed method was validated by the experimental and engineering data analysis. The results of the analysis indicate that the proposed method can identify accurately different gear health conditions. Moreover, the identification accuracy of the proposed method is higher than that of traditional multiscale Lempel–Ziv complexity (MLZC) and several representative multiscale entropies (e.g., multiscale dispersion entropy (MDE), multiscale permutation entropy (MPE) and multiscale sample entropy (MSE)).     

Determination of Meloxicam Using Europium Sensitized Luminescence in the Presence of Co-Luminescence Reagents

A sensitive time- resolved luminescence method for the determination of meloxicam (MX) in methanol and in aqueous solution is described. The method is based on the luminescence sensitization of europium (Eu³⁺) by formation of ternary complex with MX in the presence of 1,10- phenanthroline as coligand, Tween-80 as surfactant and gadolinium ion as a co-luminescence reagent. The signal for Eu- MX-1, 10- phenanthroline is monitored at λ_ex = 360 nm and λ_em = 620 nm. Optimum conditions for the formation of the complex in aqueous system were 0.01 M TRIS buffer, pH 8.0, 1,10- phenanthroline (6.0 × 10⁻⁶ M) , Gd³⁺ (7.0 × 10⁻⁶ M), Tween-80 (0.28%) and 1.75 mM of Eu³⁺ which allows the determination of 20–800 ppb of MX with limit of detection (LOD) of 7 ppb. The relative standard deviations of the method range between 0.1 and 1.1% indicating excellent reproducibility of the method. The proposed method was successfully applied for the assay of MX in pharmaceutical formulations, plasma and in urine samples. Average recoveries of 99.8 ± 1.1%, 100.2 ± 0.9% and 100.9 ± 1.1% were obtained for MX in tablet, plasma and urine sample respectively.     

Evaluation of Transparent Optical Network Performance in Presence of Incoherent Homodyne Crosstalk

Abstract

A simple method to evaluate the performance of transparent optical networks (TON) that takes into account the incoherent homodyne crosstalk, signal distortion, inter-symbol interference (ISI), amplified spontaneous emission (ASE) noise, and arbitrary optical and electrical filters is proposed. This method combines the effect of the incoherent homodyne crosstalk with an exhaustive Gaussian approximation for the influence of ASE noise, signal distortion, and ISI. It is shown that the incoherent homodyne crosstalk penalty depends on the ASE noise accumulated in the TON, ISI, and extinction ratio. The proposed method estimates are compared with experimental results published by other authors. Good agreement is observed for one, two, and four incoherent homodyne crosstalk signals, revealing that the proposed method provides accurate estimates even when the methods based on a Gaussian approximation for the incoherent homodyne crosstalk fail. The proposed method is used to assess the performance of a TON composed by optical add-drop multiplexers based on arrayed waveguide gratings. Results reveal that incoherent homodyne crosstalk, ASE noise, and ISI impair the TON performance and, therefore, none can be neglected in the TON design.     

Ultrasonic distance and velocity measurement using a pair of LPM signals for cross-correlation method: improvement of Doppler-shift compensation and examination of Doppler velocity estimation

Real-time distance measurement of a moving object with high accuracy and high resolution using an ultrasonic wave is difficult due to the influence of the Doppler effect or the limit of the calculation cost of signal processing. An over-sampling signal processing method using a pair of LPM signals has been proposed for ultrasonic distance and velocity measurement of moving objects with high accuracy and high resolution. The proposed method consists of cross correlation by single-bit signal processing, high-resolution Doppler velocity estimation with wide measurement range and low-calculation-cost Doppler-shift compensation. The over-sampling cross-correlation function is obtained from cross correlation by single-bit signal processing with low calculation cost. The Doppler velocity and distance of the object are determined from the peak interval and peak form in the cross-correlation function by the proposed method of Doppler velocity estimation and Doppler-shift compensation. In this paper, the proposed method of Doppler-shift compensation is improved. Accuracy of the determined distance was improved from approximately within ±140 μm in the previous method to approximately within ±10 μm in computer simulations. Then, the proposed method of Doppler velocity estimation is evaluated. In computer simulations, accuracy of the determined Doppler velocity and distance were demonstrated within ±8.471 mm/s and ±13.87 μm. In experiments, Doppler velocities of the motorized stage could be determined within ±27.9 mm/s.     

简明分数阶傅里叶变换及其对线性调频信号的检测和参数估计

针对低信噪比下线性调频信号的检测问题,提出了一种简明分数阶傅里叶变换方法。该变换借助chirp相乘和傅里叶变换对时频平面上的频率轴进行旋转,以获取信号在各个角度下频率轴上的频谱分布。对时频分布呈直线状的线性调频信号,简明分数阶傅里叶变换能在特定角度上将信号能量聚集成尖锐的强能量峰,从而提高信噪比,实现对线性调频信号的可靠检测和参数估计。数值仿真和实验验证结果表明,简明分数阶傅里叶变换可对较低信噪比的线性调频信号实现有效检测,并由变换域峰值的位置对信号参数进行准确估计。相比于传统的分数阶傅里叶变换方法,简明分数阶傅里叶变换的复杂度更低,离散计算效率更高,在对噪声掩盖下的线性调频信号进行检测和参数估计时能更好地满足实时处理的要求。      

Influence of the lens effect in a sample with large dielectric constant in a loop-gap resonator on the EPR signal intensity at 700 MHz

The influence of the lens effect on the electron paramagnetic resonance (EPR) signal intensity was investigated in a loop-gap resonator (LGR) with an inner diameter of 41 mm. TheQ- value and EPR signal intensity were measured when the phantoms containing 3-carbamoyl-2,2,5,5-tetramethyl-pyrrolidin-l-yloxy dissolved in sodium chloride aqueous solutions were put in the LGR. TheQ- value and signal intensity reduced with increasing concentrations of sodium chloride in the phantom, indicating that the imaginary part of the dielectric constant is larger in the phantom with the higher concentration of sodium chloride. However, relationships betweenQ-values of the resonator and EPR signal intensities were not proportional and signal intensities were relatively higher compared with theQ-values. These findings suggest that the signal reduction due to lowQ is slightly compensated by the lens effect in the sample with the large real part of the dielectric constant. In the distribution of the signal intensities of a pinpoint sample made of diphenylpicrylhydrazyl in the agar medium containing sodium chloride in the LGR, it was found that the signal intensity decreased according to the distance from the center and the difference in the signal intensity within 10 mm from the center was about 20%, indicating the inhomogeneity of the alternating magnetic field at the center and marginal region in the sample with the large dielectric constant caused by the lens effect.