Instantaneous Distortions Research Articles

Empirical mode decomposition and Hilbert–Huang transform-based eccentricity fault detection and classification with demagnetization in 120 kW interior permanent magnet synchronous motors

Permanent magnet synchronous motors (PMSMs) are extensively used in electric vehicles (EVs) owing to their high power density and efficiency. However, their safety and reliability have not been verified sufficiently. Failure of PMSMs in EVs can cause performance degradation, increased maintenance costs, and catastrophic accidents. Therefore, early detection of faults in PMSMs is necessary for an efficient and safe operation. In this study, static, dynamic, and mixed eccentricity faults in 120 kW interior permanent magnet synchronous motors (IPMSMs) were diagnosed and distinguished from uniform demagnetization fault by monitoring the Hilbert spectrum of the stator current. Experiments were carried out for different speeds, loads, and fault severities to analyze the effect of operating conditions on the proposed fault detection method. The phase current data were decomposed into set of intrinsic mode functions (IMFs) with empirical mode decomposition (EMD) method and Hilbert transform was applied for each IMFs to calculate the instantaneous frequency and energy. The resultant Hilbert spectrum exhibited instantaneous frequency distortions with an instantaneous energy surge under an eccentricity fault. The effect of thresholding in EMD was analyzed to improve the accuracy of the proposed method under high-load and high-speed conditions. Also, the experimental results showed that eccentricity and uniform demagnetization faults can be classified by monitoring the overall instantaneous energy.

Modelling the Delayed Nonlinear Fiber Response in Coherent Optical Communications

Fiber nonlinearities, that lead to nonlinear signal interference (NLI), are typically regarded as an instantaneous material response with respect to the optical field. However, in addition to an instantaneous part, the nonlinear fiber response consists of a delayed contribution, referred to as the Raman response. The imaginary part of its Fourier transform, referred to as the Raman gain spectrum, leads to inter-channel stimulated Raman scattering (ISRS). ISRS is a nonlinear effect that redistributes optical power from high to lower frequencies during propagation. However, as the nonlinear fiber response is causal, the Raman spectrum obeys the Kramers-Kronig relations resulting in the real part of the complex valued Raman spectrum. While the impact of the imaginary part (i.e. ISRS) is well studied, the direct implications of its associated real part on the NLI are unexplored. In this work, a theory is proposed to analytically quantify the impact of the real Raman spectrum on the nonlinear interference power. Starting from a generalized Manakov equation, an extension of the ISRS Gaussian Noise (GN) model is derived to include the real Raman spectrum and, thus, to account for the complete nonlinear Raman response. Accurate integral expressions are derived and approximations in closed-form are proposed. Different formulations for the case of single -and dual polarized signals are derived and novel analytical approximations of the real Raman spectrum are proposed. Moreover, it is analytically shown that the real Raman spectrum scales the strength of the instantaneous nonlinear distortions depending on the frequency separation of the interacting frequencies. A simple functional form is derived to assess the scaling of the NLI strength. The proposed theory is validated by numerical simulations over C-and C+L band, using experimentally measured fiber data.

Discount Rate Regulation for Canadian Private Defined Benefit Pension Plans

Due to scarcity of long-term market instruments, valuation of private defined-benefit (DB) pension liabilities requires an extrapolation of yield curve. In Canada, corporate yields are adopted to discount private DB pension liabilities, but issue on how to extrapolate yield curve beyond market liquid point has not been clearly addressed in regulatory guidance. This paper introduces a macroeconomic extrapolation method called the Canadian ultimate forward rate to complete yield curve. The new method effectively reduces valuation volatility for it is robust against interpolation models and instantaneous market distortions.

Sub-50 fs excited state dynamics of 6-chloroguanine upon deep ultraviolet excitation.

The photophysical properties of natural nucleobases and their respective nucleotides are ascribed to the sub-picosecond lifetime of their first singlet states in the UV-B region (260-350 nm). Electronic transitions of the ππ* type, which are stronger than those in the UV-B region, lie at the red edge of the UV-C range (100-260 nm) in all isolated nucleobases. The lowest energetic excited states in the UV-B region of nucleobases have been investigated using a plethora of experimental and theoretical methods in gas and solution phases. The sub-picosecond lifetime of these molecules is not a general attribute of all nucleobases but specific to the five primary nucleobases and a few xanthine and methylated derivatives. To determine the overall UV photostability, we aim to understand the effect of more energetic photons lying in the UV-C region on nucleobases. To determine the UV-C initiated photophysics of a nucleobase system, we chose a halogen substituted purine, 6-chloroguanine (6-ClG), that we had investigated previously using resonance Raman spectroscopy. We have performed quantitative measurements of the resonance Raman cross-section across the Bb absorption band (210-230 nm) and constructed the Raman excitation profiles. We modeled the excitation profiles using Lee and Heller's time-dependent theory of resonance Raman intensities to extract the initial excited state dynamics of 6-ClG within 30-50 fs after photoexcitation. We found that imidazole and pyrimidine rings of 6-ClG undergo expansion and contraction, respectively, following photoexcitation to the Bb state. The amount of distortions of the excited state structure from that of the ground state structure is reflected by the total internal reorganization energy that is determined at 112 cm(-1). The contribution of the inertial component of the solvent response towards the total reorganization energy was obtained at 1220 cm(-1). In addition, our simulation also yields an instantaneous response of the first solvation shell within an ultrafast timescale of less than 30 fs following photoexcitation.

English

When a light beam propagates through the turbulent atmosphere, the wavefront of the beam is distorted, which affect the image quality of ground based telescopes. Adaptive optics is a means for real time compensation of the wavefront distortions. In an adaptive optics system, wavefront distortions are measured by a wavefront sensor, and then using an active optical element such as a deformable mirror the instantaneous wavefront distortions are corrected. In this paper, the physical background of imaging through turbulence, using Kolmogorov statistics, and the Polarization Shearing Interferometry techniques to sense and to correct the wavefront aberrations with adaptive optics have been discussed. Simulations of the interferometric records were carried out using Matlab for the study of aberrations in an optical system and the effect of the atmospheric turbulence in the interferograms. The data was reduced from the interferogram using Fourier Transform Technique and the wavefront was reconstructed from the wavefront slope data

Finite temperature effects on the X-ray absorption spectra of lithium compounds: first-principles interpretation of X-ray Raman measurements.

We elucidate the role of room-temperature-induced instantaneous structural distortions in the Li K-edge X-ray absorption spectra (XAS) of crystalline LiF, Li2SO4, Li2O, Li3N, and Li2CO3 using high resolution X-ray Raman spectroscopy (XRS) measurements and first-principles density functional theory calculations within the eXcited electron and Core Hole approach. Based on thermodynamic sampling via ab initio molecular dynamics simulations, we find calculated XAS in much better agreement with experiment than those computed using the rigid crystal structure alone. We show that local instantaneous distortion of the atomic lattice perturbs the symmetry of the Li 1s core-excited-state electronic structure, broadening spectral line-shapes and, in some cases, producing additional spectral features. The excellent agreement with high-resolution XRS measurements validates the accuracy of our first-principles approach to simulating XAS, and provides both accurate benchmarks for model compounds and a predictive theoretical capability for identification and characterization of multi-component systems, such as lithium-ion batteries, under working conditions.

Local structure correlations in plastic cyclohexane—a reverse Monte Carlo study

Two solid phases of cyclohexane have been investigated over a temperature range spanning 13–266 K on a powdered, perdeuterated sample using neutron total scattering. Phase II has an ordered structure (C2/c) that forms below 186 K. Between 186 and 280 K it exists as a plastic solid—phase I (Fm3m), where the molecules are rotationally disordered about the lattice points of the face-centred cubic cell. Data-dependent atomistic configurations that represent the ‘instantaneous’ crystal structure have been generated from the total scattering data using reverse Monte Carlo refinement. Analysis of the local structure reveals that instantaneous distortions in phase I resemble the average structure of phase II.

Electronic signature of the instantaneous asymmetry in the first coordination shell of liquid water

Interpretation of the X-ray spectra of water as evidence for its asymmetric structure has challenged the conventional symmetric nearly tetrahedral model and initiated an intense debate about the order and symmetry of the hydrogen-bond network in water. Here we present new insights into the nature of local interactions in water obtained using a novel energy-decomposition method. Our simulations reveal that although a water molecule forms, on average, two strong donor and two strong acceptor bonds, there is a significant asymmetry in the energy of these contacts. We demonstrate that this asymmetry is a result of small instantaneous distortions of hydrogen bonds, which appear as fluctuations on a time scale of hundreds of femtoseconds around the average symmetric structure. Furthermore, we show that the distinct features of the X-ray absorption spectra originate from molecules with high instantaneous asymmetry. Our findings have important implications as they help reconcile the symmetric and asymmetric views on the structure of water.

Anomalous Wetting Layer at the Au(111) Surface

In this paper we present a microscopic picture of the interface between liquid water and a Au(111) surface at room temperature conditions, as obtained from ab initio molecular dynamics simulations. We find that the first wetting layer has peculiar structural and electronic features that can be revealed only by considering the dynamical evolution of the system. Surface phonons and molecular vibrations lead to instantaneous charge density distortions that are pivotal to explain the features of such an atypical wetting layer, and, in turn, the surface hydrophilicity.

Capturing and Analyzing the Excited-State Structure of a Cu(I) Phenanthroline Complex by Time-Resolved Diffraction and Theoretical Calculations

Time-resolved crystallography and density functional theory calculations are used to analyze the geometric and electronic changes that occur upon photoexcitation of [Cu(I)(dmp)(dppe)](+) in crystalline [Cu(I)(dmp)(dppe)][PF(6)] [dmp = 2,9-dimethyl-1,10-phenanthroline; dppe = 1,2-bis(diphenylphosphino)ethane]. In the pump-probe experiment, laser and X-ray pulses are synchronized to capture an image of the instantaneous molecular distortions in the transient triplet state. Parallel theoretical calculations, with the phenyl groups replaced by methyl groups, yield information on the distortion of the isolated cation and the change in electron density upon excitation. The experimental distortions are significantly less than the calculated values and are different for the two independent molecules in the asymmetric unit; these findings are attributed to the constraining influence of the crystal matrix. The calculations indicate that the electron transfer upon excitation is mostly from the dmpe ligand to the dmp ligand, while the Cu atomic charge changes by only approximately +0.1e, although the charge distribution on Cu is significantly affected. As found for homoleptic [Cu(I)(dmp)(2)](+), the change in the population of the Cu atom is close to the calculated difference between the corresponding Cu(II) and Cu(I) complexes. Charge density difference maps confirm these conclusions and show a large rearrangement of the electron density on the Cu atom upon excitation.

Practical Considerations in Restoring Images from Phase‐Diverse Speckle Data

ABSTRACTWe discuss practical problems and solutions associated with the “phase‐diverse” speckle (PDS) imaging technique for reconstruction of high‐resolution images from ground‐based telescope data. The PDS method uses an ensemble of short‐exposure images obtained simultaneously from multiple cameras to jointly estimate the object and the sequence of instantaneous phase distortions observed by each camera. Different known static phase aberrations are imposed on each optical channel; the known aberrations then function as constraints in the estimation problem. In this paper, we extend a previously derived model and present new data calibration techniques to compensate for various undesirable effects present in real‐world PDS data. These effects include relative tip‐tilt and image magnification changes between the diversity channels. The extended model and its associated (modified) objective functions lead to a new nonlinear optimization problem. Solution methods, software, and results using real telescope data are discussed.

Lattice fluctuations and inhomogeneous charge states of high-Tc superconductors

We have used x-ray absorption spectroscopy as a tool to study instantaneous local lattice distortions of the CuO2 plane in high-Tc superconductors and we have investigated the inhomogeneous charge states of these materials. The temperature-dependent Cu K-edge extended x-ray absorption fine structure (EXAFS) has been used to determine the correlated Debye–Waller factor of the Cu–O bonds, measuring local lattice fluctuations. The Debye–Waller factor of the Cu–O bonds shows an order-parameter-like behaviour across the charge stripe ordering temperature. The EXAFS results are supported by a temperature-dependent Cu K-edge x-ray absorption near edge structure (XANES) revealing a particular change in the local lattice displacements at the charge stripe ordering. The experimental Cu K-edge XANES results are well reproduced by full multiple scattering calculations including different distortions of the CuO2 plane showing particular lattice displacements which are consistent with the EXAFS results. The particular distortion mode as a response function to the charge stripe ordering has been discussed with several examples. The results are consistent with an inhomogeneous charge distribution in the high-Tc cuprates suggesting an intimate relationship between the charge stripe ordering, local lattice fluctuations and high-Tc superconductivity in the cuprates.

Improved method for estimation of the maximum instantaneous distortion values

In this article a statistical method for estimating the maximum instantaneous distortion values is developed further to estimate the maximum values of the instantaneous distortions in which the operation of peak values of dynamic pressures and correlation between them are involved. The effects of the correlation between fluctuating pressures on the estimation are discussed. Comparison between the estimated values and the experimental results shows that the developed method can quite accurately estimate the maximum value of the instantaneous distortion with operation of peak values of dynamic pressures involved, such as the distortion descriptor DC(sub theta). The accuracy estimation of maximum instantaneous distortion can generally be improved by considering the correlations between fluctuation pressures. However, when the mean correlation coefficient rho(bar) is less than 0.1, the estimation can be effected by dispensing with correlation. 4 refs.

Novel use of molecular dynamics simulation in studying structure–property relationships in the solid infrared laser medium Na+–Er3+β″-alumina

X-Ray diffraction studies have been made of the crystalline luminescent material Na+–Er3 +β″-alumina for three different erbium ion concentrations; equivalent to 100, 72 and 26% substitution of Na+ ions (Na1+y–3xErxMgyAl11–yO17, for x= 0.56, 0.40 and 0.14, respectively, and y= 2/3). The results form thereafter a structural basis for molecular dynamics (MD) simulations, which, in turn, are used to calculate crystal-field parameters needed for Judd–Ofelt analyses of the optical absorption spectra. The Er3+ ions behave somewhat differently from other rare-earth ions in the Na+β″-alumina host in that they can occupy two different sites in the conduction plane. Judd–Ofelt intensity parameters are calculated using a point-charge model for different concentrations and temperatures, and agree well with experimentally determined parameters. This agreement is because the local instantaneous distortions around the rare-earth ions are properly accounted for when using atomic positions taken from an MD simulation.

Estimation of the maximum instantaneous distortion

IN this synoptic, a new statistical method of estimating the maximum instantaneous inlet pressure distortion is described. By this method, the time average and root-meansquare (rms) values of the instantaneous pressure distortion index Ke, Krad, and KA2 can be obtained analytically from the measured inlet total steady-state pressure and rms values. The most probable maximum instantaneous distortion index that occurs in a given duration can also be obtained. Comparison between the estimated values and the experimental results shows that the described method can estimate accurately the maximum instantaneous distortion index with 3 s on an Intel 86/330 microcomputer. Contents In the evaluation of inlet and engine compatibility of a new aircraft, the maximum instantaneous pressure distortions of the intake are usually estimated in the earlier stages of the development to forecast whether they are greater than the allowable values of the engine. There are three well-known statistical estimating methods discussed in Ref. 1. In this paper, the time average and rms values of the instantaneous distortion index K6, Krad, and KA2 are obtained analytically from inlet total steady-state pressure and rms measurements beforehand. By assuming that the amplitude probability density distribution of the distortion index is Gaussian, the most probable probability with which the maximum instantaneous distortion value occurs in a given duration and the maximum instantaneous distortion itself are found. This method is of practical value if the distortion pattern that pertained to the maximum instantaneous distortion is not indispensable as in the preliminary design stage of the intake. The distortion index K can usually be expressed as

Ground Vortex–Limit to Engine/Reverser Operation

It has been commonly accepted that engine stalls during reverser operation are caused by the temperature distortion created by reingested exhaust gasses. Recent studies have shown that compressors respond to instantaneous inlet distortions of a time duration on the order of one engine revolution. This paper describes the results of a test of a high bypass ratio engine during reverse thrust operation which revealed, through the use of high response temperature and pressure measurement, that instantaneous distortions caused by an induced ground vortex were the cause of engine stalls.