Spectral Peak Frequency Research Articles

Characterization of Falcon 9 launch vehicle noise from far-field measurements.

This study investigates source-related noise characteristics of the Falcon 9, a modern launch vehicle with a high operational tempo. Empirical prediction of the noise characteristics of launched rockets has long been a topic of study; however, there are relatively few comparisons with high-fidelity, far-field data, and historical inconsistencies persist. Various quantities are considered: overall directivity, overall sound power, maximum overall sound pressure level (OASPL), and peak frequency. The noise directivity of the Falcon 9 vehicle is shown to be between two disparate ranges given in the historical literature, but the observed peak directivity angle is well represented using convective Mach number concepts. A comparison between mechanical and acoustic power yields a radiation efficiency is consistent with the literature. Two independent methods of predicting maximum OASPL produce results accurate within 2 dB, even at distances of several kilometers. Various scaling parameters are calculated for observed spectral peak frequency and connect these measurements with prior observations. Finally, the impact of terrain shielding on levels and spectra is assessed. These determined source characteristics of the Falcon 9 vehicle provide a connection to prior launch vehicle acoustics studies, which helps identify useful models and methods for understanding rocket noise.

Correlating Beta Oscillations from Intraoperative Microelectrode and Postoperative Implanted Electrode in Patients Undergoing Subthalamic Nucleus Deep Brain Stimulation for Parkinson Disease; A Feasibility Study

We sought to investigate the feasibility of intraoperative local field potential (LFP) recording from the microelectrode during deep brain stimulation surgery for patients with Parkinson disease. Sixteen subthalamic nucleus recordings from 10 Parkinson disease patients who underwent deep brain stimulation surgery were included in this study. Signals from microelectrodes were amplified and differently filtered to display real-time single-unit neuronal activity and LFP simultaneously during surgery. LFP recordings were also recorded postoperatively from the implanted macroelectrodes and, power spectral density and peak frequency of beta oscillation of LFP (beta LFP) between 2 conditions were compared. Stable intraoperative beta LFP were observed in 68.75% (11 of 16) cases. There was no significant difference of peak frequency between intraoperative and postoperative beta-LFP but significant difference of mean percentage of beta LFP was noted between 2 conditions. Despite low signal-to-noise ratio and susceptibility to noises from external sources, this study shows that intraoperative recording of beta LFP using microelectrode is feasible. And, given that no significant difference in peak frequency of beta LFP between intraoperative and postoperative LFP was found, we suggest that not only intraoperative beta LFP can be used as a reliable surrogate for postoperative beta LFP, but it can also provide us an information for estimating the location with maximal power of beta oscillation within the subthalamic nucleus.

A study on the relationship between non-epileptic fast (40 – 200 Hz) oscillations in scalp EEG and development in children

ObjectivePhysiological gamma and ripple activities may be linked to neurocognitive functions. This study investigated the relationship between development and non-epileptic, probably physiological, fast (40–200 Hz) oscillations (FOs) including gamma (40 – 80 Hz) and ripple (80 – 200 Hz) oscillations in scalp EEG in children with neurodevelopmental disorders. MethodsParticipants were 124 children with autism spectrum disorder (ASD) and/or attention deficit/hyperactivity disorder (ADHD). Gamma and ripple oscillations were explored from 60-second-long sleep EEG data in each subject using a semi-automatic detection tool supplemented with visual confirmation and time–frequency analysis. ResultsGamma and ripple oscillations were detected in 25 (20.2%) and 22 (17.7%) children, respectively. The observation of one or more occurrence(s) of ripple oscillations, but not gamma oscillations, was significantly related to lower age at EEG recording (odds ratio, OR: 0.727 [95% confidence interval, CI: 0.568–0.929]), higher intelligence/developmental quotient (OR: 1.041, 95% CI: 1.002–1.082), and lack of a diagnosis with ADHD (OR: 0.191, 95% CI: 0.039 – 0.937) according to a binominal logistic regression analysis that included diagnosis with ASD, sex, history of perinatal complications, history of febrile seizures, and use of a sedative agent for the EEG recording as the other non-significant parameters. Diagnostic group was not related to frequency or power of spectral peaks of FOs. ConclusionThe production of non-epileptic scalp ripples was confirmed to be associated with brain development and function/dysfunction in childhood. Further investigation is necessary to interpret all of the information on higher brain functions that may be embedded in scalp FOs.

Interacting brains coming in sync through their minds: an interbrain neurofeedback study.

Neurophysiological evidence shows that interpersonal action coordination is accompanied by interbrain synchronization (IBS). However, the functional significance of this association remains unclear. Using two experimental designs, we explored whether IBS is amenable to neurofeedback (NFB). Feedback was provided either as two balls approaching each other (so-called ball design), or as two pendula, each reflecting the oscillatory activity of one of the two participants (so-called pendulum design). The NFB was provided at delta (i.e., 2.5 Hz) and theta (i.e., 5Hz) electroencephalography frequencies, and manipulated by enhanced and inverse feedback. We showed that the participants were able to increase IBS by using NFB, especially when it was fed back at the theta frequency. Apart from intra- and interbrain coupling, other oscillatory activities (e.g., power spectral density, peak amplitude, and peak frequency) also changed during the task compared with the rest. Moreover, all the measures showed specific correlations with the subjective postsurvey item scores, reflecting subjective feeling and appraisal. We conclude that the use of IBS for NFB might help in specifying the contribution of IBS to interpersonal action coordination and in providing important information about the neural mechanisms of social interaction and the causal dimension of IBS.

Multi-wave band Synchrotron Polarization of Gamma-Ray Burst Afterglows

Abstract Multi-wave band synchrotron linear polarization of gamma-ray burst (GRB) afterglows is studied under the assumption of an anisotropic turbulent magnetic field with a coherence length of the plasma skin-depth scale in the downstream of forward shocks. We find that for typical GRBs, in comparison to optical polarization, the degree of radio polarization shows a similar temporal evolution but a significantly smaller peak value. This results from differences in observed intensity image shapes between the radio and optical bands. We also show that the degree of the polarization spectrum undergoes a gradual variation from the low- to the high-polarization regime above the intensity of the spectral peak frequency, and that the difference in polarization angles in the two regimes is zero or 90°. Thus, simultaneous multi-wave band polarimetric observations of GRB afterglows would be a new determinative test of the plasma-scale magnetic field model. We also discuss theoretical implications from the recent detection of radio linear polarization in GRB 171205A with the Atacama Large Millimeter/submillimeter Array and other models of magnetic field configuration.

A set of composite, non-redundant EEG measures of NREM sleep based on the power law scaling of the Fourier spectrum

Features of sleep were shown to reflect aging, typical sex differences and cognitive abilities of humans. However, these measures are characterized by redundancy and arbitrariness. Our present approach relies on the assumptions that the spontaneous human brain activity as reflected by the scalp-derived electroencephalogram (EEG) during non-rapid eye movement (NREM) sleep is characterized by arrhythmic, scale-free properties and is based on the power law scaling of the Fourier spectra with the additional consideration of the rhythmic, oscillatory waves at specific frequencies, including sleep spindles. Measures derived are the spectral intercept and slope, as well as the maximal spectral peak amplitude and frequency in the sleep spindle range, effectively reducing 191 spectral measures to 4, which were efficient in characterizing known age-effects, sex-differences and cognitive correlates of sleep EEG. Future clinical and basic studies are supposed to be significantly empowered by the efficient data reduction provided by our approach.

Insights Into the Internal Dynamics of Natural Lahars From Analysis of 3-Component Broadband Seismic Signals at Volcán de Colima, Mexico

Lahar monitoring on active volcanoes is challenging, and the ever changing environment leads to inconsistent results that hamper a warning systems ability to characterize the flow event properly. Therefore, more data, new methods, and the use of different sensors needs to be tested, which could lead to improvements in warning capabilities. Here, we present data from a 3-component broadband seismometer and video camera installed 3 m from the Lumbre channel on Volcán de Colima, Mexico to understand rheology differences within multiple lahar events that occurred in late 2016. We examine differences in frequency and directionality from each seismic component. Results indicate an increase in peak frequency above background in each component when a lahar nears the sensor, and a decrease in overall peak frequency when transitioning from a streamflow to a higher concentration flow. The seismic frequency distribution for the cross-channel component for the streamflow has a wider range compared with the lahar events. In contrast, the peak spectral frequency of the streamflow is narrower in comparison to the lahar events in the flow parallel and vertical directions. Estimated directionality ratios (cross-channel signal divided by flow parallel signal) yielded further evidence for a rheologic change between streamflow and lahars. Directionality ratios >1 were calculated for each lahar, and <1 for streamflow. Finally, we demonstrate from component analyses that channelization or freedom of movement in the cross-channel, bedload transport in the flow parallel, and bed composition in the vertical directions are possibly the main drivers in the peak spectral frequency output of lahars. The results described here indicate that using all three components may provide important information about lahar dynamics, which may be useful for automatic detection and warning systems, and using all three components should be encouraged.

Numerical simulations of gravitational waves from early-universe turbulence

We perform direct numerical simulations of magnetohydrodynamic turbulence in the early universe and numerically compute the resulting stochastic background of gravitational waves and relic magnetic fields. These simulations do not make the simplifying assumptions of earlier analytic work. If the turbulence is assumed to have an energy-carrying scale that is about a hundredth of the Hubble radius at the time of generation, as expected in a first-order phase transition, the peak of gravitational wave power will be in the mHz frequency range for a signal produced at the electroweak scale. The efficiency of gravitational wave (GW) production varies significantly with how the turbulence is driven. Detectability of turbulence at the electroweak scale by the planned Laser Interferometer Space Antenna (LISA) requires anywhere from 0.1% to 10% of the thermal plasma energy density to be in plasma motions or magnetic fields, depending on the model of the driving process. Our results predict a new universal form below the spectral peak frequency that is shallower than previously thought. This implies larger values of the GW energy spectra in the low-frequency range. This extends the range where turbulence is detectable with LISA to lower frequencies, corresponding to higher energy scales than the assumed energy-carrying scale.

Similarity Model Development of Spar Floating Wind Turbine for Vibration Experimental Study

As the fixed foundation wind turbine no longer meets the design and cost requirements in deep sea power plant, and the offshore floating wind turbine (FOWT) suitable has been developed rapidly. The spar FOWT model is established in ANSYS-AQWA, and the influences of spectral peak frequency and incident angle for irregular waves on the vibration responses of FOWT are studied under five load cases. Under the guidance of similar theory, 1/150 scaled model has been simulated under typical load cases. The results show that the peak frequency of the spectrum has a significant effect on the vibration responses of FOWT, the incident angle also has a slight effect. By comparing the maximum and standard deviation (SD) of the tower top fore-aft displacement (TTDspFA) with the physical model and the experimental model, the minimum errors are 3.60% and 3.56%, respectively. This work will lay a foundation for experimental study on vibration of the floating wind turbine.

Development of a Data Assimilation Method Using Vibration Equation for Large‐Eddy Simulations of Turbulent Boundary Layer Flows

AbstractIn order to improve the simulation accuracy, it is effective to use a data assimilation technique which is capable of reproducing more realistic simulated states by incorporating observational data into simulation models. One of the simplest ones among data assimilation techniques is a Newtonian relaxation‐type nudging method which has been widely used in mesoscale meteorological models. In this study, we proposed a data assimilation method using a vibration equation which can incorporate turbulence winds toward target mean winds while maintaining small‐scale turbulent fluctuations as a different approach from the conventional nudging method. First, we conducted test simulations in which nudging is applied in a basic turbulent boundary layer (TBL) flow toward a target one. It is shown that the basic TBL flow can be reasonably nudged toward the target one while maintaining the turbulent fluctuations well when prescribing the natural frequency in the vibration equation smaller than the spectral peak frequency in the TBL flow. Then, we applied the proposed nudging method by incorporating data obtained from meteorological observations located in the actual city of Kyoto. The mean wind velocity profiles were reasonably nudged toward the target observed profile and the turbulence statistics were also favorably maintained. It is concluded that the data assimilation method using the vibration equation successfully nudges toward the target mean winds while maintaining small‐scale turbulent fluctuations well.

Surface wave spectral properties of centimeter to decameter wavelengths: variable spectral slope and non-equilibrium spectrum

Understanding the wave properties in centimeter to decameter (cmDm) wavelength range is of great interest to ocean remote sensing and air-sea interaction. For more than six decades, cmDm waves are generally considered to be in the equilibrium range, and its spectral function has a constant slope: − 5 or − 4 in the 1D frequency spectrum and − 3 or − 2.5 in the 1D wavenumber spectrum. Some variations of the equilibrium spectrum model include varying the frequency spectral slope from − 4 to − 5 at some multiple of the spectral peak frequency, or incorporating a threshold velocity in the reference wind speed. Extensive efforts are then devoted to quantifying the spectral coefficient of the equilibrium spectrum function. This paper emphasizes that the observed wave spectral slope in the ocean is mostly non-constant. Therefore, the wave properties in field observations are significantly different from those inferred from assuming a constant spectral slope. The variable spectral slope is indicative of a non-equilibrium nature of ocean surface waves. Furthermore, from signal-to-noise consideration, surface slope is much more suited than elevation for evaluating the spectral slope and for quantifying the cmDm wave properties. Microwave sensors are excellent instruments for providing the ocean surface slope measurements. Several large datasets of lowpass-filtered mean square slope (LPMSS) have been reported recently. Combining the LPMSS observations with a spectrum function that accommodates a variable spectral slope, several quantitative results on the variable spectral slope and cmDm wave properties are presented.

A Characterization of Periodicity in the Voltage Time Series of a Riometer

AbstractThis paper reveals unprecedented periodicity in the voltage series of relative ionospheric opacity meters (riometers) of the Canadian Riometer Array (CRA). In quiet times, the riometer voltage series is accurately modeled by a stochastic process whose components include both a six term expansion in harmonic functions and some amplitude modulated modes of lower signal to noise ratio (SNR). In units of cycles per sidereal day (cpsd), the frequencies of the six harmonic functions lie within 0.01 cpsd of an integer. Earth's rotation induces a splitting of the low SNR components, resulting in the appearance of nine multiplets in standardized power spectrum estimates of the considered CRA voltage series. A second feature of these spectrum estimates is a 6 min periodic element appearing in both the CRA voltage series and the proton mass density series of the Advanced Composition Explorer (ACE). Spectral peak frequencies have been detected, which lie near established solar mode frequency estimates. In addition, some of these peak frequency estimates are coincident with peak frequency estimates of the standardized power spectra for the time series of proton mass density and interplanetary magnetic field strength (IMF) at ACE.

Azimuthal anisotropy analysis applied to naturally fractured unconventional reservoirs: A Barnett Shale example

Studying the seismic responses of velocity and amplitude on wide-/full-azimuth seismic data is now common for unconventional reservoir characterization. Velocity variation with azimuth (VVAz) and amplitude variation with azimuth (AVAz) are two of the most popular tools to map not only the relative intensity and orientation of natural fractures but also the strength and orientation of the maximum horizontal stress SH. We prestack time migrated a wide-azimuth Barnett Shale survey in North Texas into eight azimuths and reduced noise on the gathers using prestack structure-oriented filtering. We then computed the envelope, spectral peak frequency, and prestack P-wave impedance attributes for each azimuthally limited seismic volume. We compensated the VVAz effects by flattening each sector along the Barnett Shale key horizons, thereby registering the gathers for subsequent AVAz analysis. The results indicate the intensity, orientation, and confidence of azimuthal anisotropy effects on seismic velocity and amplitude, which can be referred to smaller scale vertical cracks or natural fractures. Our analysis reveals four zones of high anisotropy intensity that can be tied to either the regional structures or paleo stress field. Analysis of production data indicate from the anisotropy interpretation results that vertical, sealed fractures are the dominant cause of anisotropy and those specific fractures inhibit production. This observation and results indicate that horizon-based azimuthal anisotropy analysis avoids the VVAz effect and can be applied to fractures and regional stress field prediction.

Estimation of Direction of Arrival of Biological Sound using Acoustic Vector Sensor Array in Shallow Water off Chennai

Mahanty, M.M.; Latha, G.; Sridhar, P.S.S.R., and Raguraman, G., 2020. Estimation of direction of arrival of biological sound using acoustic vector sensor array in shallow water off Chennai. In: Sheela Nair, L.; Prakash, T.N.; Padmalal, D., and Kumar Seelam, J. (eds.), Oceanic and Coastal Processes of the Indian Seas. Journal of Coastal Research, Special Issue No. 89, pp. 52-57. Coconut Creek (Florida), ISSN 0749-0208.The primary objective of this study is to estimate the direction of arrival (DOA) of biological sound by using an acoustic vector sensor array, deployed in the shallow waters off Chennai during the period 30th August-14th September, 2016. A vector sensor measures the scalar acoustic pressure along with acoustic particle velocity in three orthogonal directions. Based on the spectrogram analysis, Terapontidae fish chorus is identified in distinctive patterns associated with daily timing and frequency content throughout the recording. The chorus is species-specific with the spectral peak frequency extended over 0.6-1.5 kHz in each day after dusk, and indicates these sound signals are associated with spawning. The single call duration is about 0.35-0.45 s, and comprised of a series of pulses ranging from 35-40. By considering the single call as a sound source from the recorded Terapontidae fish chorus, the DOA is determined based on conventional beamforming technique with respect to dominant frequency of that particular sound source, and estimated both azimuth and elevation using vector sensor array components. The study clearly shows the application of the vector sensor array, and can be useful to estimate source localization of the biological sound and their movement in the marine environment in future work.

Impact damage detection in composites using a guided wave mixing technique

Combined harmonics at sum- or difference-frequencies can be generated by the cross-interactions of guided wave mixing in tested samples with material nonlinearity. However, it is also observed that there are multiple combined harmonic modes generated at various mixing frequencies during the guided wave mixing process. It is still difficult to select certain combined harmonic modes to identify damage because the acoustic nonlinear response is much more complicated than the damage itself. Considering that multiple mixing frequency components can be generated during guided wave mixing, this paper investigates the feasibility of detecting impact damage in composite laminates through the combination of a guided wave mixing technique and a mixing frequency peak counting approach. Experimental observation of the combined harmonics at the mixing frequency generated by guided wave mixing clearly identifies the existence of material nonlinearity in the specimen. The present results show a monotonic increase in the correlation of the value of the mixing frequency spectral peak count with respect to the impact energy induced in the specimens. The developed technique provides an alternative for practical application of guided wave mixing for nondestructive testing in a quantizable manner.

Snow Depth Estimation with GNSS-R Dual Receiver Observation

Two estimation methods using a dual GNSS (Global Navigation Satellite System) receiver system are proposed. The dual-frequency combination method combines the carrier phase observations of dual-frequency signals, whereas the single-frequency combination method combines the pseudorange and carrier phase observations of a single-frequency signal, both of which are geometry-free strictly combination and free of the effect of ionospheric delay. Theoretical models are established in the offline phase to describe the relationship between the spectral peak frequency of the combined sequence and the antenna height. A field experiment was conducted recently and the data processing results show that the root mean squared error (RMSE) of the dual-frequency combination method is 5.04 cm with GPS signals and 6.26 cm with BDS signals, which are slightly greater than the RMSE of 4.16 cm produced by the single-frequency combination method of L1 band with GPS signals. The results also demonstrate that the proposed two combination methods and the SNR method achieve similar performance. A dual receiver system enables the better use of GNSS signal carrier phase observations for snow depth estimation, achieving increased data utilization.

Interpreting observations of ion cyclotron emission from large helical device plasmas with beam-injected ion populations

Ion cyclotron emission (ICE) is detected from all large toroidal magnetically confined fusion (MCF) plasmas. It is a form of spontaneous suprathermal radiation, whose spectral peak frequencies correspond to sequential cyclotron harmonics of energetic ion species, evaluated at the emission location. In ICE phenomenology, an important parameter is the value of the ratio of energetic ion velocity to the local Alfvén speed . Here we focus on ICE measurements from heliotron-stellarator hydrogen plasmas, heated by energetic proton neutral beam injection (NBI) in the large helical device, for which takes values both larger (super-Alfvénic) and smaller (sub-Alfvénic) than unity. The collective relaxation of the NBI proton population, together with the thermal plasma, is studied using a particle-in-cell (PIC) code. This evolves the Maxwell–Lorentz system of equations for hundreds of millions of kinetic gyro-orbit-resolved ions and fluid electrons, self-consistently with the electric and magnetic fields. For LHD-relevant parameter sets, the spatiotemporal Fourier transforms of the fields yield, in the nonlinear saturated regime, good computational proxies for the observed ICE spectra in both the super-Alfvénic and sub-Alfvénic regimes for NBI protons. At early times in the PIC treatment, the computed growth rates correspond to analytical linear growth rates of the magnetoacoustic cyclotron instability (MCI), which was previously identified to underlie ICE from tokamak plasmas. The spatially localised PIC treatment does not include toroidal magnetic field geometry, nor background gradients in plasma parameters. Its success in simulating ICE spectra from both tokamak and, here, heliotron-stellarator plasmas suggests that the plasma parameters and ion energetic distribution at the emission location largely determine the ICE phenomenology. This is important for the future exploitation of ICE as a diagnostic for energetic ion populations in MCF plasmas. The capability to span the super-Alfvénic and sub-Alfvénic energetic ion regimes is a generic challenge in interpreting MCF plasma physics, and it is encouraging that this first principles computational treatment of ICE has now achieved this.

Sound change and coarticulatory variability involving English /ɹ/

English /ɹ/ is known to exhibit covert variability, with tongue postures ranging from bunched to retroflex, as well as various degrees of lip protrusion and compression. Because of its articulatory variability, /ɹ/ is often a focal point for investigating the role of individual variation in change. In the studies reported here, we examine the coarticulatory effects of alveolar obstruents with /ɹ/, presenting data from a collection of sociolinguistic interviews involving 162 English speakers from Raleigh, North Carolina, and a pilot corpus of ultrasound and lip video from 29 additional talkers. These studies reveal a mixture of assimilatory and coarticulatory patterns. For the sound changes in progress (/tɹ/ and /dɹ/ affrication, and /stɹ/ retraction), we find increases over apparent time, but no effect of covert variability in our laboratory data, consisting mostly of younger talkers. When a sound change has already become phonologized to a new phonemic target with a correspondingly different articulatory target, the original variability is obscured. In comparison, post-lexical coarticulation of word-final /s z/ before a word-initial /ɹ/ more closely resembles /s z/ in tongue posture, with an effect of anticipatory lip-rounding that introduces a low-mid frequency spectral peak during the sibilant interval, and greater reduction in the frequency of this peak for talkers who transition more rapidly to the /ɹ/. In order to uncover the role of covert variability in a sound change, we must look to sounds that exhibit synchronically stable articulatory variability.

P66-F Resting-state source-space MEG detects hippocampal hyperactivity in amyloid-positive amnestic MCI

Background Early detection of pathological hippocampal hyperactivity in persons with Mild Cognitive Impairment (MCI) and positive AD biomarkers (CSF/PET) is desirable, but no method is available. Here, we test MEG-based detection of hippocampal activity in MCI patients with positive biomarkers for AD, hypothesizing that their levels will be higher than in controls and AD patients. Method We used resting-state MEG recordings from 18 AD patients (age 63.8 ± 6.5, 9 females, mean MMSE 17.9), 18 amyloid-positive amnestic MCI patients (age 64.1 ± 6.2, 10 females, mean MMSE 25.8) and 18 persons with subjective cognitive decline (SCD, age 64.2 ± 6.1, 10 females, mean MMSE 27.6). Group and regional differences in spectral power and peak frequency were identified. Patient data was compared with computational model simulations of hyperactivity. Results Peak frequency was similar in SCD and MCI groups, but lower in AD patients. MCI showed a strong increase in absolute and relative lower alpha (8–10 Hz) power, strongest in the (right) hippocampus. Gamma (30–45 Hz) relative power decreased in MCI. In all groups, absolute hippocampal power was larger than the mean, especially in the (right) hippocampus. Group classification was most accurate using hippocampal power in the gamma band. Hyperactivity simulations produced changes fitting the MCI data, supporting hyperactivity as interpretation. Conclusion Our results support pathological neuronal activity increases in preclinical AD. Significant changes in the hippocampus and gamma band show the additional value of MEG. Besides diagnostic and trial patient selection relevance, this finding is valuable for activity-targeting therapy research in AD.

Wake dynamics and surface pressure variations on two-dimensional normal flat plates

The relationship between vortex dynamics and surface pressure fluctuations on the leeward face of a two-dimensional normal thin flat plate was studied using Direct Numerical Simulations for incompressible flow at a Reynolds number of 1200. The vortex shedding frequency was observed in the spectra of pressure fluctuations on both faces of the plate, while a lower frequency spectral peak was only evident on the leeward pressure fluctuations. Local sharp peaks of low pressure in the separated shear layers coincide with increases in the leeward face pressure fluctuations. These observations are tied to the vortex dynamics using the invariant Q, commonly used for vortex identification. Q is also proportional to the source term for the Poisson equation for the instantaneous pressure. The pressure, which is the only contributor to the plate drag, varies significantly in response to alterations to the vortex shedding, which can be observed in differences of vortex trajectories. At minimum drag, the pressure fluctuations are small, which is attributed to lower values of Q associated with weaker vortices.