DMUSIC algorithm for 2D NMR signals

Li, Y.; Razavilar, J.; Liu, K.J.R.

doi:10.1109/iembs.1995.575208

Cited by 5 publications

(8 citation statements)

References 1 publication

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“…The DMusic algorithm [20,21] is used to calculate spectrograms that allow us to identify modes in the phase contrast imaging (PCI), soft X-ray multi-camera tomography system (XMCTS) [24], and Mirnov measurements. The SSI tool (stochastic system identification) [22,23] can also detect common frequencies in an array of time signals and extract poloidal mode numbers.…”

Section: Analysis Toolsmentioning

confidence: 99%

“…The SSI tool (stochastic system identification) [18,19] can also detect common frequencies in an array of time signals and extract poloidal mode numbers. Shear Alfvén continua are computed by the CONTI [20] code. Given the knowledge of the location of the frequency gaps, we can use CKA [1] to find discrete eigenmodes in these gaps.…”

Section: Analysis Toolsmentioning

confidence: 99%

“…Recently, such tools (which already existed for other problems in mathematics, physics, or civil engineering) have been adapted for applications in plasma physics [19]. We present here the application of the DMusic algorithm [20,21], a powerful tool to generate spectrograms, to our experimental data. This tool provides a much better visibility of the signal in the frequency domain than an FFT-based method would.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of mode activity in NBI-heated experiments of Wendelstein 7-X

et al. 2020

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The 2018 operation phase (OP 1.2b) of the stellarator Wendelstein 7-X (W7-X) included, for the first time, neutral beam injection (NBI) to heat the plasma. Since the injection geometry at W7-X is not parallel, this generates both passing and trapped fast particles. During longer phases of NBI injection, with the primary purpose to study the heating efficiency of this system, Alfvén eigenmodes (AEs) were observed by a number of diagnostics, including the phase contrast imaging (PCI) system, the magnetic pick-up coils (Mirnov coils), and the soft X-ray multi-camera tomography system (XMCTS).Alfvén eigenmodes are of great interest for future fusion reactors as it has been shown that the resonant interaction of fast ions with self-excited AEs can lead to enhanced transport of fast ions and potentially to energy losses. This is especially true for so-called gap-modes, Alfvén eigenmodes with frequencies in gaps of the continuous spectrum, since they lack continuum damping. These modes are commonly known to be excited by fast ions, but other destabilizing mechanisms, e.g. the electron-pressure gradient are also possible.In this article we present a first analysis of the experimentally observed frequencies from the theoretical side. The calculation of shear Alfvén wave continua for selected cases and the assignment of observed frequencies to the gaps of the continuous spectra are presented. Using the ideal-MHD code CKA [1], we find gap modes that match the experimental measurements in terms of the observed frequencies. We emphasize the crucial roles played by the coupling of sound and Alfvén waves as well as of the Doppler shift arising as a consequence of the radial electric field in W7-X.We employ the perturbative gyrokinetic code CKA-EUTERPE [2], using a slowing-down distribution function for the fast ions as calculated by the Monte-Carlo particle following code ASCOT [3] to assess the fast-ion drive. We find that the fast-ion drive is insufficient to overcome the background-plasma damping. The fact that unstable modes were observed experimentally may point to problems with the modelling or indicate the existence of other destabilizing mechanisms, e.g. associated with the electron-pressure gradient [4] that sensitively depend on the profiles of the background plasma.

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Section: Analysis Toolsmentioning

confidence: 99%

Section: Analysis Toolsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigation of mode activity in NBI-heated experiments of Wendelstein 7-X

et al. 2020

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“…Damped MUSIC (DMUSIC) has been proposed as a two-dimensional super-resolution method for estimating the parameters of the DE model in the context of nuclear magnetic resonance (NMR) spectroscopy [14,15]. For such an application, the estimated frequencies and damping factors are usually used in determining the structure of organic compounds.…”

Section: Principlementioning

confidence: 99%

Subspace Leakage Suppression for Joint Parameter Estimation of Quality Factors and Time Delays in Dispersive Media

Chahine

Baltazart²,

Wang

2015

Circuits Syst Signal Process

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International audienceLinear prediction methods, based on a Hankel data matrix, suffer fromsubspace leakage and degraded resolution when applied to data models that do notresult in a mode matrix with Vandermonde structure, such as the constant-Q model.In the absence of noise, the Vandermonde structure ensures the equivalence betweenthe number of backscattered signals and the rank of the data matrix. This paper firstidentifies the origin of subspace leakage residing in subspace-based and linear predictionmethods when applied to data of the constant-Q model. Second, it proposesa frequency-distortion technique, based on the extension theorems, for suppressingthe leakage and preserving the time resolution performance of these methods. Theeffectiveness of the distortion technique is then demonstrated on GPR simulated databy extending the damped MUSIC algorithm to the joint parameter estimation of theconstant-Q model

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“…Additionally, they usually require the sources to be uncorrelated. In order to improve the availability of subspace methods in single snapshot (or single measurement vector, SMV) and/or correlated cases, spatial smoothing based techniques are introduced, such as the iterative spatial smoothing (ISS) algorithm [10], the weighted spatial smoothing (WSS) algorithm [11], the spatial difference smoothing (SDS) algorithm [12] and the damped MUSIC (DMUSIC) algorithm [37]. With smoothing, subspace methods work for correlated and/or SMV sources at the cost of reducing the effective array aperture size and hence sacrificing the resolution.…”

Section: Introductionmentioning

confidence: 99%

A Novel Gradient Descent Least Squares (GDLS) Algorithm for Efficient SMV Gridless Line Spectrum Estimation with Applications in Tomographic SAR Imaging

Shi¹,

Zhang²,

Qiu³

et al. 2022

Preprint

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This paper presents a novel efficient method for gridless line spectrum estimation problem with single snapshot, namely the gradient descent least squares (GDLS) method. Conventional single snapshot (a.k.a. SMV measurement) line spectrum estimation methods either rely on smoothing techniques that sacrifice the array aperture, or adopt the sparsity constraint and utilize compressed sensing (CS) method by defining prior grids and resulting in the off-grid problem. Recently emerged atomic norm minimization (ANM) methods achieved gridless SMV line spectrum estimation, but its computational complexity is extremely high; thus it is practically infeasible in real applications with large problem scales. Our proposed GDLS method reformulates the line spectrum estimations problem into a least squares (LS) estimation problem and solves the corresponding objective function via gradient descent algorithm in an iterative

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DMUSIC algorithm for 2D NMR signals

Cited by 5 publications

References 1 publication

Investigation of mode activity in NBI-heated experiments of Wendelstein 7-X

Investigation of mode activity in NBI-heated experiments of Wendelstein 7-X

Subspace Leakage Suppression for Joint Parameter Estimation of Quality Factors and Time Delays in Dispersive Media

A Novel Gradient Descent Least Squares (GDLS) Algorithm for Efficient SMV Gridless Line Spectrum Estimation with Applications in Tomographic SAR Imaging

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