Oblique chirp sounding of the modified ionosphere. Experiment and simulation

We present the results of experimental studies of the influence of artificial ionospheric disturbances on HF signals used for oblique sounding of the disturbed volume. The measurements have been performed by a chirp ionosonde over the path Yoshkar-Ola-“Sura”-niznhy Novgorod with length 234 km. We found the 2F2 mode to disappear (attenuation up to 20 dB) when the ionosphere is influenced by a vertical powerful radiation in the ordinary mode with long (15 min each) heating and pause intervals. Modeling of the observed effect was carried out. The calculations agree well with experimental data if the traveling ionospheric disturbances (TID) with vertical and horizontal scales l_z∼20 km and l_x∼50 km, respectively, and the relative disturbance of the electron density δN∼0.2–0.3 are amplified (generated) during the ionosphere heating. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 4, pp. 303–313, April 1999.     

遗传算法与最小二乘法在实验数据处理中的对比研究

采用遗传算法拟合甘油的黏度随温度的变化公式,并将得到的经验公式与采用传统的最小二乘法得到的公式比较.发现在处理某些非线性拟合问题时,采用最小二乘法并非最好,遗传算法得到的结论更优,方法也更简单.     

A least squares quantization table method for direct reconstruction of MR images with non-Cartesian trajectory

The direct Fourier transform method is a straightforward solution with high accuracy for reconstructing magnetic resonance (MR) images from nonuniformly sampled k-space data, given that the optimal density compensation function is selected and the underlying magnetic field is sufficiently uniform. The computation however is very time-consuming, making it impractical especially for large-size images. In this paper, the least squares quantization table (LSQT) method is proposed to accelerate the direct Fourier transform computation, similar to the recently proposed methods such as using look-up table (LUT) or equal-phase-line (EPL). With LSQT, all the image pixels are first classified into several groups where the Lloyd-Max quantization scheme is used to ensure the minimal classification error. The representative value of each group is stored in a small-size LSQT in advance to reduce the computational load. The pixels in the same group receive the same contribution, which is calculated only once for each group instead of for each pixel, resulting in the reduction of computation because the number of groups is far smaller than the number of pixels. Finally, each image pixel is mapped into the nearest group and its representative value is used to reconstruct the image. The experimental results show that the LSQT method requires far smaller memory size than the LUT method and fewer multiplication operations than the LUT and EPL methods. Moreover, the LSQT method can perform large-size reconstructions that achieve comparable or higher accuracy as compared to the EPL and gridding methods when the appropriate parameters are given. The inherent parallel structure also makes the LSQT method easily adaptable to a multiprocessor system.     

基于拉曼光谱和最小二乘支持向量机的橄榄油掺伪检测方法研究

为实现橄榄油中掺伪油类型的识别和掺伪量预测,对掺入葵花籽油、大豆油、玉米油的橄榄油共117个样品进行拉曼光谱检测,并用基于多重迭代优化的最小二乘支持向量机模型对掺入油的类型进行识别,综合识别率为97%。同时分别采用最小二乘支持向量机、人工神经网络模型、偏最小二乘回归建立橄榄油中葵花籽油、大豆油、玉米油含量的拉曼光谱定标模型,结果显示最小二乘支持向量机具有最优的预测效果,其预测均方根误差(RMSEP)在0.007 4～0.014 2之间。拉曼光谱结合最小二乘支持向量机可为橄榄油掺伪检测提供一种精确、快速、简便、无损的方法。     

Optical transmission inspection of the basis weight using the piecewise least squares method and quality capability of process

This article explores a method of optical transmission inspection of the basis weight on-line, by combining the modified least squares and optical processing technique. This process is developed to significantly target toward improving the mass quality analysis of the nonwoven material. The real-time scanning width piecewise least squares method and area-based strategy for determining based on the process quality of nonwoven manufacturing. To avoid the influence of ambient factors, the compensation controls device are adopted and successfully showed. Subsequently, the modified least squares method is used to obtain the suitable parameter transformation between the measured voltage and the nonwoven fabrics basis weight. The piecewise least squares method was obtained as the parameter transfer equation. We consider estimating and testing C_pk with the presence of on-line basis weight measurement errors. To obtain the true process precision C_p and integrated process capability index C_pk are presented to practitioners for their factory applications.     

Viewing the effective k-space coverage of MR images: phantom experiments with fast Fourier transform

The purpose of this experimental study was to evaluate whether the effective k-space coverage of MR images can in principle be viewed after multidimensional Fourier transform back to k-space.     

液氢加注系统中过滤器漏热故障仿真与分析

液氢管道输送需要在极低温度下进行,需要较高的保温措施,而且出现漏热故障的时候将十分危险.发生漏热后的液氢会迅速产生气液两相流,其对加注系统中的器件造成很大的冲击与危害,造成加注系统损坏等事故.因此,对液氢加注系统进行仿真研究有着重要的作用.而过滤器漏热的影响大约是管道漏热的三倍,所以研究过滤器漏热更具有防范风险的指导意义.本文依据AMEsim工程仿真软件,对液氢加注系统进行建模与仿真,并置入过滤器故障仿真进行对比与分析.     

热敏电阻温度特性仿真实验的教学分析

大学物理仿真实验是把实验设备,教学内容,教师指导和学习者的思考、操作有机融合为一体,为物理实验改革提供了有力的途径;学生运用多媒体和计算机模拟技术,进行模拟操作、数据处理和分析思考,理解和掌握实验原理和方法.但同时仿真实验也存在有一定的弊端.通过仿真实验热敏电阻温度特性的典型教学,以及调查和分忻,得出了仿真实验在实验教学中的消极影响,并提出了一些需要注意的问题,为大学物理实验改革提供新思路.     

Scatterer size estimation in pulse-echo ultrasound using focused sources: calibration measurements and phantom experiments

In a companion paper [T. A. Bigelow and W. D. O'Brien Jr., J. Acoust. Soc. Am. 116, 578 (2004)], theory, supported by simulations, showed that accurate scatterer size estimates could be obtained using highly focused sources provided that the derived generalized attenuation-compensation function was used and the velocity potential field near the focus could be approximated as a three-dimensional Gaussian. Herein, the theory is further evaluated via experimental studies. A calibration technique is developed to find the necessary equivalent Gaussian dimensions for a focused source using reflections obtained from a rigid plane scanned through the focus. Then, the theoretical analysis of focused sources is validated experimentally using three spherically focused ultrasound transducers to estimate the radius of glass beads imbedded in tissue mimicking phantoms. Both the impact of focusing (f/1, f/2, and f/4) and the effect of scatterer type (comparing glass bead results to simulation results that used scatterers with Gaussian impedance distributions) were tested. The simulated differences agree with the measured differences to within 2.5% provided that the comparison is made between the same scatterer type and sources with the same equivalent Gaussian dimensions. The improvement provided by the generalized attenuation-compensation function is greatly influenced by the type of scatterer whose size is being estimated and decreases as the wavelength dependence of the Gaussian depth of focus is reduced.     

Manipulation of nanoparticles using dynamic force microscopy: simulation and experiments

82 , M = Sc, Y, La) are discussed. The first ¹³C hyperfine structure has been analyzed in detail and at least seven electronically different groups of carbon atoms could be assigned by simulations of the ESR spectra. The strong similarity of the ¹³C satellite structure suggests the preference of one cage isomer for the scandium group C₈₂ endohedrals. The geometric structure and the electronic structure of all nine fullerene cage isomers of La@C₈₂ were studied by approximate density-functional-based theoretical calculations. A C_3v isomer was found as the most stable one. The manifold of ¹³C hyperfine coupling constants could be interpreted on the basis of the calculated spin density distributions. Received: 15 September 1997/Accepted: 16 October 1997     

基于近红外的多相偏最小二乘模型组合分析实现茶叶原料品种鉴定与溯源的研究

为实现茶叶的品种溯源,以近红外光谱分析技术为基础,尝试采用PLS、欧氏距离等方法的组合来实现茶叶的特殊原料品种的鉴别、具体品种识别分析。结果表明:研究中以4个品种(龙井43,群体种、迎霜和乌牛早)的茶树鲜叶为制成的茶叶样本为材料,分别建立了4个不同原料加工成的茶叶样本的PLS鉴定模型,对定标集样本识别的准确率分别为89.8%,90.9%,96.1%和99.5%,验证集的识别准确率分别为87.1%,84.2%,96.1%和97.5%;而采用4个品种鉴定模型的组合分析初次识别并且结合欧氏距离法进行二次识别后,最终对4种不同品种茶叶样本的原料品种的识别准确率分别为90.3%(定标集)和83.5%(验证集)。该研究为实现特殊品种加工成茶叶的鉴定以及成品茶的品种溯源提供了一种参考方法。     

An analysis on the effect of the equalizer parameters in a direct-modulation optical communication system employing an all-pass filter to combat chirp and dispersion

We consider the effect of the equalizer parameters in the performance of a direct modulated high-bit-rate communication system where the degrading combination of fibre dispersion and source chip is compensated using an all-pass optical filter.     

Weighted least squares,polyad analyses,and theoretical consistency: A demonstrative example: The 12CH3F molecule

A comprehensive approach of the simultaneous analysis of several complex vibrational polyads in polyatomic molecules is presented. Specific points regarding theoretical models and weighted least-squares procedures are discussed with the aim of determining a unique set of parameter values for reproducing all available data on a given molecule. The simultaneous analysis of the dyad $\text{ν}{}_2\text{ν}{}_5$ and the pentad $\text{ν}{}_1\text{/ν}{}_4\text{/2ν}{}_2\text{/ν}{}_2\text{+}\text{ν}{}_5\text{2ν}{}_5$ of ¹²CH₃F using microwave and infrared data is reported as an illustration.     

Transient heat conduction analysis using the MLPG method and modified precise time step integration method

The meshless local Petrov–Galerkin (MLPG) method in conjunction with the modified precise time step integration method in the time domain is proposed for transient heat conduction analysis in this paper. The MLPG method is often referred to as a truly meshless method because it requires no elements or background cells for either field interpolation or background integration. Local weak forms are developed using weighted residual method locally from the partial differential equation of transient heat conduction. In order to simplify the treatment of essential boundary conditions, the natural neighbour interpolation (NNI) is employed for the construction of trial functions. Moreover, the three-node triangular FEM shape functions are taken as test functions to reduce the order of integrands involved in domain integrals. The semi-discrete heat conduction equation is solved numerically with modified precise time step integration method in the time domain. The availability and accuracy of the present method for transient heat conduction analysis are tested through numerical examples.     

A numerical simulation method and analysis of a complete thermoacoustic-Stirling engine

Thermoacoustic prime movers can generate pressure oscillation without any moving parts on self-excited thermoacoustic effect. The details of the numerical simulation methodology for thermoacoustic engines are presented in the paper. First, a four-port network method is used to build the transcendental equation of complex frequency as a criterion to judge if temperature distribution of the whole thermoacoustic system is correct for the case with given heating power. Then, the numerical simulation of a thermoacoustic-Stirling heat engine is carried out. It is proved that the numerical simulation code can run robustly and output what one is interested in. Finally, the calculated results are compared with the experiments of the thermoacoustic-Stirling heat engine (TASHE). It shows that the numerical simulation can agrees with the experimental results with acceptable accuracy.     

Characterization of a wavelength selection method using near-infrared spectroscopy and partial least squares with false nearest neighbors and its application in the detection of the chemical oxygen demand of waste liquid

Abstract

The spectral wavelength selection method is important in near-infrared spectroscopy. Eliminating redundant information and extracting useful information can improve the prediction accuracy and modeling efficiency of the quantitative analysis model for spectral analysis to obtain a near-infrared calibration model with strong predictability and good robustness. This paper proposes a wavelength selection method for near-infrared spectroscopy by combining the partial least squares and false nearest neighbor methods. In this method, the correlation between the characteristic wavelength variables and the measured index is assessed by means of a similarity-based distance measure of the characteristic wavelength variable, and the characteristic wavelength is selected according to the order of the correlation. The method was used to select characteristic wavelengths from the near-infrared spectrum of waste liquid to establish a prediction model for the chemical oxygen demand. Compared with the full-spectrum partial least squares and interval partial least squares based models, the number of characteristic wavelength variables is reduced from 1557 to 176, and the prediction accuracy of the model is improved. This method both simplifies the model and achieves higher prediction accuracy. Therefore, this study provides a novel solution for wavelength selection for multivariate calibration in near-infrared spectroscopy.     

Multispectral 3D phase-encoded turbo spin-echo for imaging near metal: Limitations and possibilities demonstrated by simulations and phantom experiments

To see improvements in the imaging performance near biomaterial implants we assessed a multispectral fully phase-encoded turbo spin-echo (ms3D-PE-TSE) sequence for artifact reduction capabilities and scan time efficiency in simulation and phantom experiments.For this purpose, ms3D-PE-TSE and ms3D-TSE sequences were implemented to obtain multispectral images (± 20 kHz) of a cobalt-chromium (CoCr) knee implant embedded in agarose. In addition, a knee implant computer model and the acquired ms3D-PE-TSE images were used to investigate the possibilities for scan time acceleration using field-of-view (FOV) reduction for off-resonance frequency bins and compressed sensing reconstructions of undersampled data. Both acceleration methods were combined to acquire a + 10 kHz frequency bin in a second experiment.The obtained ms3D-PE-TSE images showed no susceptibility related artifacts, while ms3D-TSE images suffered from hyper-intensity artifacts. The limitations of ms3D-TSE were apparent in the far off-resonance regions (±[10–20] kHz) located close to the implant. The scan time calculations showed that ms3D-PE-TSE can be applied in a clinically relevant timeframe (~ 12 min), when omitting the three central frequency bins. The feasibility of CS acceleration for ms3D-PE-TSE was demonstrated using retrospective reconstructions before combining CS and rFOV imaging to decrease the scan time for the + 10 kHz frequency bin from ~ 10.9 min to ~ 3.5 min, while also increasing the spatial resolution fourfold. The temporally resolved signal of ms3D-PE-TSE proved to be useful to decrease the intensity ripples after sum-of-squares reconstructions and increase the signal-to-noise ratio.The presented results suggest that the scan time limitations of ms3D-PE-TSE can be sufficiently addressed when focusing on signal acquisitions in the direct vicinity of metal implants. Because these regions cannot be measured with existing multispectral methods, the presented ms3D-PE-TSE method may enable the detection of inflammation or (pseudo-)tumors in locations close to the implant.     

Fatigue in thin-film ferroelectrics: simulation by a modified diffusion-limited aggregation model with drift

Fatigue in thin-film ferroelectrics has been simulated by using a two-dimensional modified diffusion-limited aggregation model with drift representing the applied alternating electric field. It is shown that the fatigue process follows a power law at early times and speeds up dramatically at later times. Besides, it was found revealed that the fatigue rate can be lower when the drift strength becomes higher. This curious result, which has some experimental evidences, has been explained by noting that the fatigued units pattern for a higher drift strength has a larger fractal dimension.     

On the iteration of a rational function: Computer experiments with Newton's method

Using Newton's method to look for roots of a polynomial in the complex plane amounts to iterating a certain rational function. This article describes the behavior of Newton iteration for cubic polynomials. After a change of variables, these polynomials can be parametrized by a single complex parameter, and the Newton transformation has a single critical point other than its fixed points at the roots of the polynomial. We describe the behavior of the orbit of the free critical point as the parameter is varied. The Julia set, points where Newton's method fail to converge, is also pictured. These sets exhibit an unexpected stability of their gross structure while the changes in small scale structure are intricate and subtle.