Largest Spectral Peak Research Articles

Perceptual sensitivity to spectral properties of earlier sounds during speech categorization.

Recent sounds can change what speech sounds we hear later. This can occur when the average frequency composition of earlier sounds differs from that of later sounds, biasing how they are perceived. These "spectral contrast effects" are widely observed when sounds' frequency compositions differ substantially. We reveal the lower limit of these effects, as +3 dB amplification of key frequency regions in earlier sounds was enough to bias categorization of the following vowel or consonant sound. Speech categorization being biased by very small spectral differences across sounds suggests that spectral contrast effects occur frequently in everyday speech perception.

Localization of beta and high-frequency oscillations within the subthalamic nucleus region.

Parkinsonian bradykinesia and rigidity are typically associated with excessive beta band oscillations in the subthalamic nucleus. Recently another spectral peak has been identified that might be implicated in the pathophysiology of the disease: high-frequency oscillations (HFO) within the 150–400 Hz range. Beta-HFO phase-amplitude coupling (PAC) has been found to correlate with severity of motor impairment. However, the neuronal origin of HFO and its usefulness as a potential target for deep brain stimulation remain to be established. For example, it is unclear whether HFO arise from the same neural populations as beta oscillations. We intraoperatively recorded local field potentials from the subthalamic nucleus while advancing DBS electrodes in 2 mm steps from 4 mm above the surgical target point until 2 mm below, resulting in 4 recording sites. Data from 26 nuclei from 14 patients were analysed. For each trajectory, we identified the recording site with the largest spectral peak in the beta range (13–30 Hz), and the largest peak in the HFO range separately. In addition, we identified the recording site with the largest beta-HFO PAC. Recording sites with largest beta power and largest HFO power coincided in 50% of cases. In the other 50%, HFO was more likely to be detected at a more superior recording site in the target area. PAC followed more closely the site with largest HFO (45%) than beta power (27%). HFO are likely to arise from spatially close, but slightly more superior neural populations than beta oscillations. Further work is necessary to determine whether the different activities can help fine-tune deep brain stimulation targeting.

Doppler-based motion compensation algorithm for focusing the signature of a rotorcraft

A computationally efficient algorithm was developed and tested to compensate for the effects of motion on the acoustic signature of a rotorcraft. For target signatures with large spectral peaks that vary slowly in amplitude and have near constant frequency, the time-varying Doppler shift can be tracked and then removed from the data. The algorithm can be used to preprocess data for classification, tracking, and nulling algorithms. The algorithm was tested on rotorcraft data. The average instantaneous frequency of the first harmonic of a rotorcraft was tracked with a fixed-lag smoother. Then, state space estimates of the frequency were used to calculate a time warping that removed the effect of a time-varying Doppler shift from the data. The algorithm was evaluated by analyzing the increase in the amplitude of the harmonics in the spectrum of a rotorcraft. The results depended upon the frequency of the harmonics and the processing interval duration. Under good conditions, the results for the fundamental frequency of the target (~11 Hz) almost achieved an estimated upper bound. The results for higher frequency harmonics had larger increases in the amplitude of the peaks, but significantly lower than the estimated upper bounds.

Non-destructive stiffness detection of utility wooden poles using wireless MEMS sensor

This paper presents the design of a portable wireless measurement system for the non-destructive stiffness detection of wooden poles using MEMS sensor. Low cost capacitive micro-machined accelerometer is mounted on the surface of wooden poles and data collected from the vibrating wooden poles are used for the stiffness analysis of wooden poles. Fast Fourier transform is applied to the collected acceleration data records and the largest spectral peak is identified based on the estimated frequency spectrum. The relationship between the stiffness of a wooden pole and the largest spectral peak is provided. Health conditions of wooden poles are then derived based on the identified spectral peak. Fuzzy logic is also used to solve the problem of small samples. Experimental results and the accuracy of the method are also presented.

Robust spectral analysis of videocapsule images acquired from celiac disease patients

BackgroundDominant frequency (DF) analysis of videocapsule endoscopy images is a new method to detect small intestinal periodicities that may result from mechanical rhythms such as peristalsis. Longer periodicity is related to greater image texture at areas of villous atrophy in celiac disease. However, extraneous features and spatiotemporal phase shift may mask DF rhythms.MethodThe robustness of Fourier and ensemble averaging spectral analysis to compute DF was tested. Videocapsule images from the distal duodenum of 11 celiac patients (frame rate 2/s and pixel resolution 576 × 576) were analyzed. For patients 1, 2, ... 11, respectively, a total of 10, 11, ..., 20 sequential images were extracted from a randomly selected time epoch. Each image sequence was artificially repeated to 200 frames, simulating periodicities of 0.2, 0.18, ..., 0.1Hz, respectively. Random white noise at four different levels, spatiotemporal phase shift, and frames with air bubbles were added. Power spectra were constructed pixel-wise over 200 frames, and an average spectrum was computed from the 576 × 576 individual spectra. The largest spectral peak in the average spectrum was the estimated DF. Error was defined as the absolute difference between actual DF and estimated DF.ResultsFor Fourier analysis, the mean absolute error between estimated and actual DF was 0.032 ± 0.052Hz. Error increased with greater degree of random noise imposed. In contrast, all ensemble average estimates precisely predicted the simulated DF.ConclusionsThe ensemble average DF estimate of videocapsule images with simulated periodicity is robust to noise and spatiotemporal phase shift as compared with Fourier analysis. Accurate estimation of DF eliminates the need to impose complex masking, extraction, and/or corrective preprocessing measures.

Chaos and generalised multistability in a mesoscopic model of the electroencephalogram

We present evidence for chaos and generalised multistability in a mesoscopic model of the electroencephalogram (EEG). Two limit cycle attractors and one chaotic attractor were found to coexist in a two-dimensional plane of the ten-dimensional volume of initial conditions. The chaotic attractor was found to have a moderate value of the largest Lyapunov exponent (3.4 s −1 base e ) with an associated Kaplan–Yorke (Lyapunov) dimension of 2.086. There are two different limit cycles appearing in conjunction with this particular chaotic attractor: one multiperiodic low amplitude limit cycle whose largest spectral peak is within the alpha band (8–13 Hz) of the EEG; and another multiperiodic large-amplitude limit cycle which may correspond to epilepsy. The cause of the coexistence of these structures is explained with a one-parameter bifurcation analysis. Each attractor has a basin of differing complexity: the large-amplitude limit cycle has a basin relatively uncomplicated in its structure while the small-amplitude limit cycle and chaotic attractor each have much more finely structured basins of attraction, but none of the basin boundaries appear to be fractal. The basins of attraction for the chaotic and small-amplitude limit cycle dynamics apparently reside within each other. We briefly discuss the implications of these findings in the context of theoretical attempts to understand the dynamics of brain function and behaviour.

Underwater and in-air sounds from a small hovercraft

Underwater and in-air recordings were made from a boat anchored near Prudhoe Bay, Alaska, while a Griffon 2000TD hovercraft drove by at or near full power on four passes. At the closest point of approach (CPA, 6.5m), underwater broadband (10–10000Hz) levels reached 133 and 131dB re: 1μPa at depths of 1 and 7m, respectively. In-air unweighted and A-weighted broadband (10–10000Hz) levels reached 104 and 97dB re: 20μPa, respectively. The hovercraft produced sound at a wide range of frequencies. Both underwater and in air, the largest spectral peak was near 87Hz, which corresponded to the blade rate of the thrust propeller. In addition, the spectral composition included several harmonics of this frequency. The shaft or blade rate of the lift fan was barely detectable underwater despite its proximity to the water. The hovercraft was considerably quieter underwater than similar-sized conventional vessels and may be an attractive alternative when there is concern over underwater sounds.

A study of protein oxidative products using a pyrolysis-membrane inlet quadrupole ion trap mass spectrometer with air as the buffer gas

Pyrolysis-membrane inlet mass spectrometry has been used to investigate the oxidative products of several peptides in an air buffered quadrupole ion trap mass spectrometer. Results indicate that ion-molecule reactions can occur with solvent species present, forming adducts in the mass spectrometer. In addition, products resulting from oxidative pyrolysis may appear to be ion-molecule additions. Using isotopically labeled standards, different buffer gases and tandem mass spectrometry, two major oxidation products were determined to occur from proteins. Tyrosyl and phenylalanyl residues present in peptides and proteins were found to produce p-methoxybenzaldehyde and benzaldehyde upon oxidative thermal degradation. Subsequent analyte enhancement by the membrane inlet produced large mass spectral peaks characteristic of these amino acid species, when present. This paper details the investigation into the source and mechanism leading to the formation of some of these products.

DPCM coding of spectral amplitudes without positive slope overload

The author considers the problem of coding the spectral amplitudes of a sinusoidal transform coding (STC) vocoder operating at 2400 b/s, which was previously considered by R.J. McAulay and T.F. Quatieri (1987). Differential pulse code modulation (DPCM) coding of spectral amplitudes in vocoders can cause formant clipping because of positive slope overload. The author presents a modified DPCM coder that prevents positive slope overload by anticipating large spectral peaks. When the vocoder is used on speech taken from a standard telephone set, a time-varying distortion of the low-end frequencies is observed. When the modified DPCM coder is applied to the telephone-set speech, its success was obvious. The time-varying distortion of the low-end frequencies is eliminated. Performance of the STC vocoder on the telephone-set speech is essentially identical to its performance on flat-frequency-response speech.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Angle Resolved Inverse Photoemission from Ag(111) and Pd(111)

Angle resolved inverse photoemission from Ag(111) and Pd(111) surfaces has been recorded in the isochromat mode at 9.8 and 10.8 eV photon energies. Unusually large spectral peaks are found in the energy range 10-20 eV above EF. It is shown that a good qualitative description of the results is provided by a simple model based on k-conserving transitions between free-electron like states. In particular we find no structures due to elastic diffuse scattering.

Spectral studies of geomagnetic pulsations with periods between 20 and 120 sec, and their relationship to the plasmapause region

Digital spectrograms have been computed for 18 days of geomagnetic pulsation activity at three UK Earth current stations ( L = 2.6−3.6). Three main conclusions are drawn: (1) There are days when the period of the dominant spectral amplitude is ordered according to the observatory latitude. The most frequently observed large amplitude spectral peaks are centred on 80, 60 and 45s for South Uist ( L = 3.6), Eskdalemuir ( L = 3.1) and East Anglia ( L = 2.6). respectively. (2) There are other days when the period of the dominant spectral amplitude is the same at all the observatories. (3) When Pc 3 and 4 period waves have been detected together, the latitude dependence of the amplitudes supports the theory that the shorter period pulsation is enhanced in the plasmatrough while the longer period wave is enhanced within the plasmasphere.

Correlated magnetic field and plasma observations of the Earth's bow shock

Ion spectrums and magnetograms obtained simultaneously when the Vela 3A satellite crossed the earth's bow shock have been correlated. An intermediate form of ion spectrum, representing neither solar wind nor magnetosheath, but characterized by an irregular envelope and occasional large flux peaks, is found to correspond to the appearance of large-amplitude (10-25 γ), irregular magnetic oscillations of 4-to 30-sec period. The large spectral flux peaks of the shock seem to result from localized transient accelerations and decelerations of the bulk of the solar wind protons. Smaller amplitude (<5 γ), longer period (20-60 seconds), generally more regular magnetic oscillations are seen in the solar wind outside the shock where the direction of flow of ion flux peaks is found to oscillate in close correlation with magnetic waves.