Estimating the subsolar magnetopause position from soft X-ray images using a low-pass image filter

The Lunar Environment heliospheric X-ray Imager(LEXI)and Solar wind Magnetosphere Ionosphere Link Explorer(SMILE)missions will image the Earth’s dayside magneto pause and cusps in soft X-rays after their respective launches in the near future,to specify glo bal magnetic reconnection modes for varying solar wind conditions.To suppo rt the success of these scientific missions,it is critical to develop techniques that extract the magnetopause locations from the observed soft X-ray images.In this research,we introduce a new geometric equation that calculates the subsolar magnetopause position(RS)from a satellite position,the look direction of the instrument,and the angle at which the X-ray emission is maximized.Two assumptions are used in this method:(1)The look direction where soft X-ray emissions are maximized lies tangent to the magnetopause,and(2)the magnetopause surface near the subsolar point is almost spherical and thus RSis nea rly equal to the radius of the magneto pause curvature.We create synthetic soft X-ray images by using the Open Geospace General Circulation Model(OpenGGCM)global magnetohydrodynamic model,the galactic background,the instrument point spread function,and Poisson noise.We then apply the fast Fourier transform and Gaussian low-pass filte rs to the synthetic images to re move noise and obtain accurate look angles for the soft X-ray pea ks.From the filte red images,we calculate RS and its accuracy for different LEXI locations,look directions,and solar wind densities by using the OpenGGCM subsolar magnetopause location as ground truth.Our method estimates RS with an accuracy of<0.3 RE when the solar wind density exceeds>10 cm-3.The accuracy improves for greater solar wind densities and during southward interplanetary magnetic fields.The method ca ptures the magnetopause motion during southwa rd interplaneta ry magnetic field turnings.Consequently,the technique will enable quantitative analysis of the magnetopause motion and help reveal the dayside reconnection modes for dynamic solar wind conditions.This technique will suppo rt the LEXI and SMILE missions in achieving their scientific o bjectives.

On low-pass digital filters in oceanography

-Two types of filters are widely used to remove semidirunal and diurnal tidal signals and other high frequency noises in oceanography. The first type of filters uses moving average with weights in time domain, and can be easily operated. Some data will be lost at each end of the time series, especially for the low low-pass filters. The second type of filters uses the discrete Fourier transform filter (DFTF) which operates in the frequency domain, and there are no data loss at the ends for the forward transform. However, owing to the Gibbs phenomenon and the discrete sampling (Nyquist effect) , ringing appears in the inverse transformed data, which is especially serious at each end. Thus some data at the ends are also discarded. The present study tries to find out what causes the ringing and then to seek for methods to overcome the ringing. We have found that there are two kinds of ringings, one is the Gibbs phenomenon, as defined before. The other is the 'Nyquist'ringing due to sampling Nyquist critical frequency. The former is due to the abrupt transition in frequency band. The Gibbs and Nyquist effects show the ringing at each end of the filtered time series. Thus, the use of a cosine taper or a linear taper on the window in the frequency domain makes the transition band smooth, so that the Gibbs phenomenon will be minimized. Before applying the Fast Fourier Transform (FFT), the original time series at each end is properly tapered by a split cosine bell that reduces significant ringing since this method limits the energy transfer from outside of the Nyquist frequency. Thus, the DFTF can be a powerful tool to suppress the signals in which we are not interested, with sharp peaks in low frequency variation and less data loss at each end.

Uncertainties of landslide susceptibility prediction: Influences of random errors in landslide conditioning factors and errors reduction by low pass filter method

In the existing landslide susceptibility prediction(LSP)models,the influences of random errors in landslide conditioning factors on LSP are not considered,instead the original conditioning factors are directly taken as the model inputs,which brings uncertainties to LSP results.This study aims to reveal the influence rules of the different proportional random errors in conditioning factors on the LSP un-certainties,and further explore a method which can effectively reduce the random errors in conditioning factors.The original conditioning factors are firstly used to construct original factors-based LSP models,and then different random errors of 5%,10%,15% and 20%are added to these original factors for con-structing relevant errors-based LSP models.Secondly,low-pass filter-based LSP models are constructed by eliminating the random errors using low-pass filter method.Thirdly,the Ruijin County of China with 370 landslides and 16 conditioning factors are used as study case.Three typical machine learning models,i.e.multilayer perceptron(MLP),support vector machine(SVM)and random forest(RF),are selected as LSP models.Finally,the LSP uncertainties are discussed and results show that:(1)The low-pass filter can effectively reduce the random errors in conditioning factors to decrease the LSP uncertainties.(2)With the proportions of random errors increasing from 5%to 20%,the LSP uncertainty increases continuously.(3)The original factors-based models are feasible for LSP in the absence of more accurate conditioning factors.(4)The influence degrees of two uncertainty issues,machine learning models and different proportions of random errors,on the LSP modeling are large and basically the same.(5)The Shapley values effectively explain the internal mechanism of machine learning model predicting landslide sus-ceptibility.In conclusion,greater proportion of random errors in conditioning factors results in higher LSP uncertainty,and low-pass filter can effectively reduce these random errors.

Comparative Study of Low-Pass Filter and Phase-Locked Loop Type Speed Filters for Sensorless Control of AC Drives

High quality speed information is one of the key issues in machine sensorless drives,which often requires proper filtering of the estimated speed.This paper comparatively studies typical low-pass filters(LPF)and phase-locked loop(PLL)type filters with respect to ramp speed reference tracking and steady-state performances,as well as the achievement of adaptive cutoff frequency control.An improved LPF-based filter structure with no ramping and steady-state errors caused by filter parameter quantization effects is proposed,which is suitable for applying LPF for sensorless drives of AC machines,especially when fixed-point digital signal processor is selected e.g.in mass production.Furthermore,the potential of adopting PLL for speed filtering is explored.It is demonstrated that PLL type filters can well maintain the advantages offered by the improved LPF.Moreover,it is found that the PLL type filters exhibit almost linear relationship between the cutoff frequency of the PLL filter and its proportional-integral(PI)gains,which can ease the realization of speed filters with adaptive cutoff frequency for improving the speed transient performance.The proposed filters are verified experimentally.The PLL type filter with adaptive cutoff frequency can provide satisfactory performances under various operating conditions and is therefore recommended.

Research on SINS Alignment Algorithm Based on FIR Filters

An inertial frame based alignment (IFBA) method is presented, especially for the applications on a rocking platform, e.g., marine applications. Defining the initial body frame as the inertial frame, the IFBA method achieves the alignment by virtue of a cascade of low-pass FIR filters, which attenuate the disturbing acceleration and maintain the gravity vector. The aligning time rests with the orders of the FIR filter group, and the method is suitable for large initial misalignment case. An alignment scheme comprising a coarse phase by the IFBA method and a fine phase by a Kalman filter is presented. Both vehicle-based and ship-based alignment experiments were carried out. The results show that the proposed scheme converges much faster than the traditional method at no cost of precision and also works well under any large initial misalignment.

基于Butterworth滤波和Haar小波变换的干涉图像齿面域分割

干涉图像中反映齿面形貌信息的齿面域被背景噪声包围,其分割精度对相位解包裹、图像配准等后续的处理步骤存在较大的影响,直接关系到最终测量结果的精度。针对齿面干涉图像边界存在杂散条纹的现象,通过分析齿面干涉条纹的分布规律,提出了一种结合Butterworth滤波和Haar小波的齿面域分割方法。最后,在本文实验条件下,通过与时域分割方法进行对比,该方法可以将齿面干涉图像的边界杂散条纹区域内解包裹相位值有错误的地方排除在有效测量区域外并且能够对其进行有效校正,证明了基于频域信息的分割方法能够有效地提高干涉图像齿面域分割的精度。

Performance Analysis of Analog Butterworth Low Pass Filter as Compared to Chebyshev Type-I Filter, Chebyshev Type-II Filter and Elliptical Filter

A signal is the entity that carries information. In the field of communication signal is the time varying quantity or functions of time and they are interrelated by a set of different equations, but some times processing of signal is corrupted due to adding some noise in the information signal and the information signal become noisy. It is very important to get the information from corrupted signal as we use filters. In this paper, Butterworth filter is designed for the signal analysis and also compared with other filters. It has maximally flat response in the pass band otherwise no ripples in the pass band. To meet the specification, 6th order Butterworth filter was chosen because it is flat in the pass band and has no amount of ripples in the stop band.

Implementing method of optimum front-end conditioner based on Butterworth filter

The front-end conditioner is an essential part of digital systems of nuclear spectrometer, which functions in two ways: (1) prevents saturation of the subsequent ADC; (2) limits the bandwidth of frequency to realize anti-aliasing. To realize the above-mentioned functions, an optimum front-end conditioner for a resistive feedback charge-sensitive preamplifier is designed. In the conditioner, the pole-zero compensation (P/Z compensation) tech- nique was used to effectively filter signals from the preamplifier. The Butterworth filter was improved after the pole-zero position was optimally set up to shape the wave of output, which tallied with the whole system. The front-end conditioner can resolve the aberration of waveform of nuclear signals in a regular Butterworth filter. Com- pared with the traditional triple-pole filtering circuitry, the circuitry of this conditioner is more compact and flexible. Moreover, its output waveform is more symmetrical and the signal-to-noise ratio (SNR) is higher. The improvement in the resolution of spectrometer is also significant.

Design of low-pass filter based on a novel defected ground structure

A novel defected ground structure （DGS） for the microstrip line is proposed in this paper. The DGS lattice has more defect parameters so that it can provide better performance than the conventional dumbbell-shaped DGS. Selectivity is improved by 97.2% with a sharpness factor of 24.6%. The method is applied to the design of a low-pass filter to confirm validity of the proposed DGS.

Compact Metamaterial Microstrip Low-Pass Filter

Complimentary hexagonal-omega structures are used to design compact, low insertion loss (IL), low pass filter with sharp cut-off. It has been designed for improvement of roll-off performance based on both μ and ε negative property of the complimentary hex-omega structure while maintaining the filter pass-band performance. By properly designing and loading the hexagonal-omega structure in the ground of microstrip line not only improve the roll-off of the low pass filter, but also reduced the filter size. The simulated results indicate that the proposed filter achieves a flat pass band with no ripples as well as selectivity of 19.68 dB/GHz, corresponding to 5-unit cells hex-omega structures. This significantly exceeds the 5.6 dB/GHz selectivity of the conventional low pass filter design, due to sub-lambda dimensions of the hex-omega structure. A prototype filter implementing area is: 0.712λg x 0.263λg, λg being the guided wavelength at 3-dB cut-off frequency (fc). The proposed filter has a size smaller by 36.2%.

Microstrip Low-Pass Elliptic Filter Design Based on Implicit Space Mapping Optimization

It is a time-consuming and often iterative procedure to determine design parameters based on fine, accurate but expensive, models. To decrease the number of fine model evaluations, space mapping techniques may be employed. In this approach, it is assumed both fine model and coarse, fast but inaccurate, one are available. First, the coarse model is optimized to obtain design parameters satisfying design objectives. Next, auxiliary parameters are calibrated to match coarse and fine models’ responses. Then, the improved coarse model is re-optimized to obtain new design parameters. The design procedure is stopped when a satisfactory solution is reached. In this paper, an implicit space mapping method is used to design a microstrip low-pass elliptic filter. Simulation results show that only two fine model evaluations are sufficient to get satisfactory results.

压力采集滤波系统在铝合金电阻点焊中的研究及应用

为了采集铝合金点焊过程中的压力变化量,实现实时监测熔核状态,提高焊点质量,设计了一种铝合金点焊压力采集的滤波系统。第一步,设计采集电路,实现对压力信号的实时采集和电平转换;第二步,通过对压力信号干扰源的分析,设计硬件滤波和软件滤波相结合的方法,以解决压力信号受干扰的问题。实验结果表明,采用本系统得到的压力波形变化平稳,能够准确反映焊接过程中的压力变化和熔核状态。采用本系统后焊点熔核直径平均值提高了10%,而且焊点无裂纹,气孔也较少。

基于巴特沃斯滤波器的特殊人群防睡眠窒息提醒装置设计

有一种特殊人群,他们在晚上处于睡眠状态时,易出现睡眠窒息现象。一旦出现睡眠窒息,将会对人体生命构成威胁。针对此问题,文章设计了一种可在睡眠窒息初期发出声、光、振动报警提示信号的系统。通过及时报警,系统能够唤醒睡眠人员,解决特殊人群面临的健康安全隐患。

对称双屏Butterworth型频率选择表面的设计

分析了对称双屏频率选择表面(FSS)结构如何实现Butterworth型FSS和获得"平顶"和"陡截止"的"矩形化"滤波特性。结合平面波展开法与互导纳法,给出了缝隙阵列导纳和缝隙阵列之间的互导纳。以Y孔形单元为例,数值计算并分析了FSS屏与中间电介质对Butterworth型FSS的影响;然后在500 mm×500 mm聚酰亚胺基底镀15μm铜膜,制作出Y孔型FSS并将其粘贴于介质两侧。用自由空间法测试其传输特性,测试结果与仿真结果基本一致。当中间电介质电厚度为2.15 mm,单元周期为7.2 mm×6.235 2 mm,臂长为3.6 mm,臂宽为0.8 mm时,双屏FSS的互导纳与单屏FSS导纳的实部相等,从而得到Butterworth型FSS。当FSS单元周期增加0.6 mm,3 dB带宽由3.5 GHz缩减为2.1GHz时,截止度增加。分析认为,对称双屏Butterworth型FSS的设计应遵循以下原则,即在满足谐振尺寸的前提下采用无加载孔径型单元且单元周期小于0.4λ,其缝隙长宽比应小于5.5,中间电介质电厚度约为0.1λ。

基于冲击法的压电式力传感器灵敏度研究

为了开展冲击力校准装置下压电式力传感器动态灵敏度的校准,介绍了基于自由落体的落锤冲击力模型和基于空气轴承悬浮支撑的水平式质量块冲击碰撞的模型;通过4阶Butterworth低通滤波,研究加速度信号波形的滤波平滑,比较了不同截止频率的滤波效果;通过激光测振仪和标准加速度计测量加速度的对比试验,研究加速度绝对测量法与比较测量法对力传感器动态灵敏度校准精度的影响。试验结果表明,激光测振仪测量加速度须通过微分解调,要选择合适上限截止频率的4阶Butterworth低通滤波器进行滤波平滑处理;激光干涉绝对法复现的动态力精度为2%,加速度计比较法复现的动态力精度为4%;激光干涉绝对法校准的灵敏度波动性比加速度计比较法校准的灵敏度波动性小。

谷粒清选损失检测信号的Butterworth高通滤波器降噪

研究了提取强噪声背景下谷粒清选损失信号的方法及其硬件实现问题。提出运用Butterworth滤波器分离机组振动噪声与谷粒信号特征,根据信号过渡带宽度及阻带衰减量确定了满足滤波性能最低阶数,通过级联方式实现了以VCVS拓扑结构为基本单元的八阶Butterworth高通滤波器。利用EWB仿真软件对该滤波器进行了模拟分析,并在联合收获机上进行了清选试验。试验结果与仿真分析结果具有良好的一致性,表明该方法能从机组强噪声背景中提取出清选损失谷粒信号的频率信息。

一种采用Butterworth滤波器原理设计的具有高鲁棒性的状态反馈系统

本文提出了一种按照ButterworthFilter原理设计的最优状态反馈系统 ,该系统具有灵活的选择截止频率 ,滤去外部高频干扰的作用 ;同时又克服了传统最优状态反馈系统鲁棒性差这一致命缺点 ,通过理论推导和仿真试验 。

Butterworth滤波器在飞行控制系统设计中的应用

研究了基于Butterworth滤波器设计思想的控制器设计方法,将这种方法应用于某飞机纵向飞行控制的设计,并进行了鲁棒性仿真研究。结果表明:该方法设计简单,只需确定一个设计参数,就可对飞行控制系统进行初期阶段设计,具有较强的工程实用价值。

全数字逆变电源IIR Butterworth数字滤波

提出了一种改进的Butterworth滤波方法,能够对逆变焊机副边反馈电流进行有效的滤波,使电流型PWM控制器能够在强干扰、高电压和大电流的恶劣环境下高速稳定地工作。首先对信号进行快速傅里叶变换,得到有用信号和噪声的频谱分布。在综合考虑了FPGA硬件实现处理速度后,设计了IIR Butterworth滤波器,结合移动中值平均滤波的方法改善了单纯Butterworth滤波器启动速度和给定变化较大时跟踪速度慢的缺点。仿真和实验结果表明,滤波器具有很好的滤波效果,较小的相移,动态响应快,能够保证逆变焊机精确可靠地工作。