Wavelet Spectrograms Research Articles

Application of brain electrical activity burst analysis method for detection of EEG characteristics in the early stage of Parkinson's disease

To develop a mathematical method of analysis and visualization of EEG based on the ROC analysis of burst electrical activity in the cerebral cortex. Using a new method of analysis of EEG burst activity, the frequency parameters of brain electrical activity have been investigated in patients in the first stage of Parkinson's disease (PD) defined by the Hoehn and Yahr scale. Patients were right-handed, with disease onset in either the right or the left side. The burst term is used in neurophysiology for the description of wave activity in EEG signals. Bursts are reflected in the local peaks of wavelet spectrograms, some of the parameters of which have been analyzed. Electrical activity of the left and right central cortex areas was investigated. The results were compared with those obtained from healthy volunteers. In PD patients, burst activity was changed in alpha- and beta bands. Compared to healthy volunteers, it was higher in alpha band 8-9 Hz and lower in upper alpha band 11-13 Hz and beta band 18-24 Hz. With regard to asymmetry of the brain in PD patients, there was the change in burst activity in both brain hemispheres. Diagrams of burst activity showed the difference between the patients with tremor onset in the left hand and tremor onset in the right hand. This suggests differences in brain electrical activity changes in patients with left-sided and right-sided disease onset. The initial results of the study demonstrate that the method of analysis and visualization based on the evaluation of certain parameters of EEG bursts is promising for the analysis of EEG features in PD patients.

Wavelet analysis of transonic buffet on a two-dimensional airfoil with vortex generators

We visualized the shock buffets on a two-dimensional transonic airfoil with and without vortex generators (VGs) by using a fast-framing focusing schlieren imaging. The focusing schlieren visualization showed that the flow three-dimensionality around the airfoil became remarkable with installing the VGs. This implies that narrow depth of focus of imaging systems was a key to accurately capture the characteristics of the shock oscillation due to the buffet for the cases with VGs. The time-resolved imaging also revealed that non-periodic components were included in the shock oscillation due to the buffet for the cases with VGs. This prevented Fourier analysis from being applied. We used wavelet analysis to extract the characteristic of the shock oscillation for the cases with VGs. The wavelet spectrograms revealed that the low-frequency oscillation having the buffet frequency was still included intermittently in the shock oscillation even when VG controlled the buffet. The rate of appearing the low-frequency oscillation increased with increasing both the interval between VGs and the angle of attack.

El Niño-southern oscillation and cassava production in Tanzania and Brazil

Konzo epidemics occur during droughts in East, Central, and Southern Africa, where the population depends almost exclusively on poorly processed cassava. Warm phases of El Nino-Southern Oscillation (ENSO) and Pacific decadal Oscillation (PDO) are associated with droughts in these areas of Africa, but with increase rainfall in South America. To further understanding of the relationship of droughts, cassava production, and konzo epidemics, this study was done to determine if there is coherence of spectra of ENSO, PDO and cassava production. Annual time series of cassava production in Tanzania and Brazil, multivariate ENSO index (MEI), and the Pacific Decadal Oscillation index (PDO) from 1961–2013 were compared. Wavelet and cross wavelet analyses of cassava production, ENSO, and PDO were performed. Warm phases of ENSO and PDO were associated with high cassava production in Tanzania, but with low cassava production in Brazil. Spectrogram of cassava showed significantly high production at periodicities of 3–9 years in Tanzania, but with significantly low production at periodicities of 2–6 years in Brazil. Cross wavelet spectrograms showed coherence of cassava production, ENSO and PDO in Tanzania and Brazil. Time-varying cyclical cassava production in Tanzania and Brazil are coupled to ENSO and PDO modes. Occurrence of droughts, high cassava production, and konzo epidemics in Tanzania are attributable to the impact of climate variability, which should be the focus of public health policies to control konzo epidemics.

AN ANALYSIS OF MAGNETOHYDRODYNAMIC INVARIANTS OF MAGNETIC FLUCTUATIONS WITHIN INTERPLANETARY FLUX ROPES

A statistical analysis of magnetic flux ropes, identified by large-amplitude, smooth rotations of the magnetic field vector and a low level of both proton density and temperature, has been performed by computing the invariants of the ideal magnetohydrodynamic (MHD) equations, namely the magnetic helicity, the cross-helicity, and the total energy, via magnetic field and plasma fluctuations in the interplanetary medium. A technique based on the wavelet spectrograms of the MHD invariants allows the localization and characterization of those structures in both scales and time: it has been observed that flux ropes show, as expected, high magnetic helicity states (|σ m | [0.6: 1]), but extremely variable cross-helicity states (|σ c | [0: 0.8]), which, however, are not independent of the magnetic helicity content of the flux rope itself. The two normalized MHD invariants observed within the flux ropes tend indeed to distribute, neither trivially nor automatically, along the curve, thus suggesting that some constraint should exist between the magnetic and cross-helicity content of the structures. The analysis carried out has further showed that the flux rope properties are totally independent of their time duration and that they are detected either as a sort of interface between different portions of solar wind or as isolated structures embedded in the same stream.

On the calculation of the Morlet wavelet used for the analysis of the dynamics of electroencephalogram signal responses

The function describing the Morlet wavelet transform used for calculating spectrograms characterizing cerebrum brain electroencephalograms is analytically integrated. It is shown that the exact integration reduces the spurious signal level, a circumstance that facilitates obtaining ridges of wavelet spectrograms.

Wavelet Transform for Spectroscopic Analysis: Application to Diols in Water.

Wavelet transform has been used to correlate spectroscopic and structural properties from trajectories obtained by ab initio molecular dynamics simulations. This method has been applied to hydrogen bond dynamics of glycols in heavy water solutions, showing how the stretching frequency of the intramolecular O-H bond changes with the intermolecular hydrogen-bond distance. The resulting wavelet spectrograms have been interpreted according to H-bond strength and stability.

Specific features of electrocardiographic information analysis based on wavelet transform

Wavelet transform is a new tool for analysis of electrocardiographic information. In this work, we consider the procedure for selection of the mother wavelet on the basis of special criteria and substantiate an improved method for ECG analysis based on wavelet transform. An algorithm for selection of mother wavelet and synthesized wavelet providing optimal wavelet transform of ECG signal is developed. It is shown that 3D wavelet spectrograms should be constructed to increase the efficiency of assessment of the state of cardiovascular system.

A comparison of three concert halls using impulse response spectrograms

Three concert halls, Symphony Hall (Boston), Concert Hall at Otis A. Singletary Center for the Arts (Univ. Kentucky, Lexington), and Konserthuset (Gothenburg, Sweden) have been investigated. The floor plans and sections of these halls are fundamentally different as are the scattering properties of the walls and ceilings of the halls. Impulse responses were recorded in a number of positions in each hall. These impulse responses were then analyzed using FFT and Wavelet spectrograms to study to what extent the obvious geometrical differences could be traced in the impulse responses. The spatial distribution of the sound in the halls was studied using a ‘‘running’’ short‐time interaural cross‐correlation technique based on the impulse responses recorded using a dummy‐head. Results show that the wavelet spectrogram yields graphs which may be slightly easier to analyze than conventional FFT spectrograms. The expected differences due to geometry are visible in the spectrograms. The short‐time interaural cross‐correlation graphs add information which also agrees with expectations.