IR spectral density of weak H-bonds involving indirect damping. I. A new approach using non-Hermitean effective Hamiltonians

Models for the distribution of the wall-pressure under a turbulent boundary layer often estimate the coherence of the cross-spectral density in terms of a product of two coherence functions. One such function describes the coherence as a function of separation distance in the mean-flow direction, the other function describes the coherence in the cross-stream direction. Analysis of data from a large-eddy simulation of a turbulent boundary layer reveals that this approximation dramatically underpredicts the coherence for separation directions that are neither aligned with nor perpendicular to the mean-flow direction. These models fail even when the coherence functions in the directions parallel and perpendicular to the mean flow are known exactly. A new approach for combining the parallel and perpendicular coherence functions is presented. The new approach results in vastly improved approximations for the coherence.

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Complex Coherence Constraint for the Definition of the Spectral Density Matrix

Journal of the IEST ◽

10.17764/1098-4321.61.1.7 ◽

2018 ◽

Vol 61 (1) ◽

pp. 7-19

Author(s):

Zhihua Liu ◽

Chenguang Cai ◽

Yan Xia ◽

Ming Yang

Keyword(s):

Density Matrix ◽

Spectral Density ◽

Random Vibration ◽

Multiple Input Multiple Output ◽

New Approach ◽

Spectral Density Matrix ◽

Multiple Input ◽

Input Multiple Output ◽

Recursive Formulas ◽

Definition Of

Abstract The cross spectral density (CSD) for a multiple-input/multiple-output (MIMO) random vibration is typically defined by the complex coherence consisting of the modulus and the phase. The purpose of this paper is to present a constraint for the complex coherence to allow the CSD to be defined more easily. The study of the complex coherence constraint is based on Cholesky decomposition of the spectral density matrix (SDM). The complex coherence must be bounded in the interior or on the boundary of a constraint circle to ensure a physically realizable random vibration. This paper proposes a new approach to define the complex coherences of the SDM by using recursive formulas based on the constraint circle.

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Condition Monitoring of Fatigue Cracks in Machinery Blades

Noise & Vibration Worldwide ◽

10.1260/095745605775220970 ◽

2005 ◽

Vol 36 (11) ◽

pp. 18-23

Author(s):

L. Gelman

Keyword(s):

Spectral Density ◽

Power Spectral Density ◽

Crack Detection ◽

Traditional Approach ◽

Fatigue Cracks ◽

Diagnostic Features ◽

New Approach ◽

Numerical Examples ◽

Power Spectral ◽

The Fourier Transform

A novel generic approach to fatigue crack diagnostics in machinery blades is proposed and employed. The approach consists of simultaneously using two new diagnostic features: the real and imaginary parts of the Fourier transform of vibroacoustical signal generated from a blade. This approach is more generic than traditional approach based on the power spectral density; the power spectral density is a particular case of the proposed approach. Numerical examples are given based on the processing of signals generated using a nonlinear model of a blade. The signals generated are the resonant vibroacoustical oscillations of cracked and uncracked blades under narrowband vibration excitation. The numerical examples show that the crack detection is more effective when using the new approach than when using the power spectral density approach. The presented experimental results are matched with the numerical results. The proposed approach offers an effectiveness improvement over the traditional approach based on power spectral density.

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A new approach to nonparametric spectral density estimation

10.32920/ryerson.14648322.v1 ◽

2021 ◽

Author(s):

Sudeshna Pal

Keyword(s):

Spectral Density ◽

Density Estimation ◽

Frequency Resolution ◽

Spectrum Estimation ◽

New Approach ◽

Spectral Density Estimation ◽

Noise Interference ◽

Novel Approach ◽

Power Spectral ◽

Noisy Signals

A novel approach to nonparametric spectral density estimation has been proposed. The approach is based on a new evaluation criterion called autocorrelation mean square error (AMSE) for power spectral density (PSD) estimates of available finite length data. Minimization of this criterion not only provides the optimum segmentation for existing PSDE approaches , but also provides a new optimum windowing within the segments that can be combined additionally to the existing methods of nonparametric PSDE. Furthermore, the problem of frequency resolution in existing PSDE methods for noisy signals has been analyzed. In the existing approaches, the additive noise and the finiteness of data which are the causes of the original loss of the frequency resolution are not treated separately. The suggested new approach to spectrum estimation takes advantage of these two different causes of the problem and tackles the problem of resolution in two steps. First, the method optimally reduces noise interference with the signal via minimum noiseless description length (MNDL). The new power spectrum estimation MNDL-Periodogram of the denoised signal is then computed via conventional indirect periodogram to improve frequency resolution.

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Correlations obtained from optical spectra of Fe-pnictides using an extended Drude-Lorentz model

10.21203/rs.3.rs-701960/v1 ◽

2021 ◽

Author(s):

Seokbae Lee ◽

Yu-Seong Seo ◽

Seulki Roh ◽

Dongjoon Song ◽

Hirosh Eisaki ◽

...

Keyword(s):

Spectral Density ◽

Density Function ◽

High Temperature Superconductors ◽

Optical Spectra ◽

Spectral Density Function ◽

Density Functions ◽

Lorentz Model ◽

Analysis Model ◽

New Approach ◽

Spectral Density Functions

Abstract We introduce an analysis model, an extended Drude–Lorentz model, and apply it to Fe-pnictide systems to extract their electron–boson spectral density functions (or correlation spectra). The extended Drude–Lorentz model consists of an extended Drude mode for describing correlated charge carriers and Lorentz modes for interband transitions. The extended Drude mode can be obtained by a reverse process starting from the electron–boson spectral density function and extending to the optical self-energy, and eventually, to the optical conductivity. Using the extended Drude–Lorentz model, we obtained the electron–boson spectral density functions of K-doped BaFe 2 As 2 (Ba-122) at four different doping levels. We discuss the doping-dependent properties of the electron–boson spectral density function of K-doped Ba-122. We also can include pseudogap effects in the model using this new approach. Therefore, this new approach is very helpful for understanding and analyzing measured optical spectra of strongly correlation electron systems, including high-temperature superconductors (cuprates and Fe-pnictides).

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A new approach to nonparametric spectral density estimation

10.32920/ryerson.14648322 ◽

2021 ◽

Author(s):

Sudeshna Pal

Keyword(s):

Spectral Density ◽

Density Estimation ◽

Frequency Resolution ◽

Spectrum Estimation ◽

New Approach ◽

Spectral Density Estimation ◽

Noise Interference ◽

Novel Approach ◽

Power Spectral ◽

Noisy Signals

A novel approach to nonparametric spectral density estimation has been proposed. The approach is based on a new evaluation criterion called autocorrelation mean square error (AMSE) for power spectral density (PSD) estimates of available finite length data. Minimization of this criterion not only provides the optimum segmentation for existing PSDE approaches , but also provides a new optimum windowing within the segments that can be combined additionally to the existing methods of nonparametric PSDE. Furthermore, the problem of frequency resolution in existing PSDE methods for noisy signals has been analyzed. In the existing approaches, the additive noise and the finiteness of data which are the causes of the original loss of the frequency resolution are not treated separately. The suggested new approach to spectrum estimation takes advantage of these two different causes of the problem and tackles the problem of resolution in two steps. First, the method optimally reduces noise interference with the signal via minimum noiseless description length (MNDL). The new power spectrum estimation MNDL-Periodogram of the denoised signal is then computed via conventional indirect periodogram to improve frequency resolution.

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Feasibility Study of a Spectral Density Modeling of Thermal Fluctuations in Mixing Tees

Fatigue, Fracture and Damage Analysis, Volume 2 ◽

10.1115/pvp2002-1326 ◽

2002 ◽

Author(s):

C. Vindeirinho

Keyword(s):

Spectral Density ◽

Temperature Difference ◽

Thermal Stresses ◽

Thermal Fluctuations ◽

Fluid Temperature ◽

Flow Rates ◽

New Approach ◽

Qualitative And Quantitative ◽

The Subject ◽

Density Modeling

In mixing tees, hot and cold fluids meet at a nozzle with different flow rates. The resulting temperature fluctuations create mechanical and thermal stresses on the pipes. Predicting the subsequent fatigue is the subject of on-going research. A new approach was developed in order to obtain a qualitative and quantitative estimate of the damage caused by a flow without necessarily acquiring measures, which is often difficult when studying flows in nuclear plant piping. Several time-series of fluid temperature from mock-up tests were studied. Four specific profiles were recognized. Internal stress was computed and fatigue was calculated according to an algorithm. The influences of the profiles, and of the temperature difference between hot and cold legs, were studied. Finally, an approach was proposed, whereby thermal fluctuations are modeled by an envelope spectral density which is transposed to the characteristics of the studied flow (standard deviation, mean temperature, cold and hot legs temperature difference, flow rate). The use of the envelope signal gives a good estimate of the thermal fluctuations but the damage is over-estimated. On-going calculations are attempting to modify the envelope spectral density to attain more realistic values.

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