Characterization of Mayer wave oscillations in functional near-infrared spectroscopy using a physiologically informed model of the neural power spectra

Significance: Mayer waves are spontaneous oscillations in arterial blood pressure that can mask cortical hemodynamic responses associated with neural activity of interest. Aim: To characterize the properties of oscillations in the fNIRS signal generated by Mayer waves in a large sample of fNIRS recordings. Further, we aim to determine the impact of short-channel correction for the attenuation of these unwanted signal components. Approach: Mayer wave oscillation parameters were extracted from 310 fNIRS measurements using the Fitting Oscillations & One-Over-F (FOOOF) method to compute normative values. The effect of short-channel correction on Mayer wave oscillation power was quantified on 222 measurements. The practical benefit of the short-channel correction approach for reducing Mayer waves and improving response detection was also evaluated on a subgroup of 17 fNIRS measurements collected during a passive auditory speech detection experiment. Results: Mayer wave oscillations had a mean frequency of 0.108 Hz, bandwidth of 0.075 Hz, and power of 3.5 μM2/Hz. The distribution of oscillation signal power was positively skewed, with some measurements containing large Mayer waves. Short-channel correction significantly reduced the amplitude of these undesired signals; greater attenuation was observed for measurements containing larger Mayer wave oscillations. Conclusions: A robust method for quantifying Mayer wave oscillations in the fNIRS signal spectrum was presented and used to provide normative parameterization. Short-channel correction is recommended as an approach for attenuating Mayer waves, particularly in participants with large oscillations.

The Branching Redesign Technique Used for Upgrading Steel-Pipes-Based Hydraulic Systems: Re-Examined

The branching technique demonstrated an effective ability to attenuate severe hydraulic-head magnitudes into existing steel-pipes-based hydraulic systems. However, there was no detailed exploration of circumferential-stress, radial-strain, and wave-oscillation period behaviors, which are equally embedded in the design stage of hydraulic systems. Accordingly, this paper examined these last parameters to provide relevant information on the entire design key parameters. The numerical solver used the Method of Characteristics for discretizing the extended one-dimensional water-hammer model incorporating the Vitkovsky and the Kelvin–Voigt formulations along with the discrete gas cavity model to represent column separation. The plastic short-penstock material types utilized in this study included high- or low-density polyethylene (HDPE or LDPE). Results demonstrated that the branching technique is promising in terms of hydraulic-head attenuation waves; however, this research emphasized the limitation of this technique, not previously delineated, including the amplification of the radial-strain peaks or crests and the spreading of the wave-oscillation period. Ultimately, a methodology was suggested for optimizing the plastic short-penstock diameter and length parameters.