intrinsic frequency
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2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Naoyuki Sato

AbstractRecent human studies using electrocorticography have demonstrated that alpha and theta band oscillations form traveling waves on the cortical surface. According to neural synchronization theories, the cortical traveling waves may group local cortical regions and sequence them by phase synchronization; however these contributions have not yet been assessed. This study aimed to evaluate the functional contributions of traveling waves using connectome-based network modeling. In the simulation, we observed stable traveling waves on the entire cortical surface wherein the topographical pattern of these phases was substantially correlated with the empirically obtained resting-state networks, and local radial waves also appeared within the size of the empirical networks (< 50 mm). Importantly, individual regions in the entire network were instantaneously sequenced by their internal frequencies, and regions with higher intrinsic frequency were seen in the earlier phases of the traveling waves. Based on the communication-through-coherence theory, this phase configuration produced a hierarchical organization of each region by unidirectional communication between the arbitrarily paired regions. In conclusion, cortical traveling waves reflect the intrinsic frequency-dependent hierarchical sequencing of local regions, global traveling waves sequence the set of large-scale cortical networks, and local traveling waves sequence local regions within individual cortical networks.


2022 ◽  
Author(s):  
Axel Gabriel

Abstract. The increase in amplitudes of upward propagating gravity waves (GWs) with height due to decreasing density is usually described by exponential growth; however, recent measurements detected a much stronger increase in gravity wave potential energy density (GWPED) during daylight than night-time (increase by a factor of about 4 to 8 between middle stratosphere and upper mesosphere), which is not well understood up to now. This paper suggests that ozone-gravity wave interaction in the upper stratosphere/lower mesosphere is largely responsible for this phenomenon. The coupling between ozone-photochemistry and temperature is particularly strong in the upper stratosphere where the time-mean ozone mixing ratio is decreasing with height; therefore, an initial uplift of an air parcel must lead to a local increase in ozone and in the heating rate compared to the environment, and, hence, to an amplification of the initial uplift. Standard solutions of upward propagating GWs with linear ozone-temperature coupling are formulated suggesting local amplitude amplifications during daylight of 5 to 15 % for low-frequency GWs (periods ≥4 hours), as a function of the intrinsic frequency which decreases if ozone-temperature coupling is included. Subsequently, for horizontal wavelengths larger than 500 km and vertical wavelengths smaller than 5 km, the cumulative amplification during the upward level-by-level propagation leads to much stronger amplitudes in the GW perturbations (factor of about 1.5 to 3) and in the GWPED (factor of about 3 to 9) at upper mesospheric altitudes. The results open a new viewpoint for improving general circulation models with resolved or parameterized GWs.


2021 ◽  
Author(s):  
Gwendal Marechal ◽  
Charly de Marez

Abstract. Recent altimeters and numerical studies have shown that wind waves interact strongly with small scale open ocean currents, and subsequently modify their amplitude, frequency, and direction. In the present paper we investigate the interactions of wind waves with a large realistic cyclonic eddy. This eddy is subject to instabilities leading to the generation of specific features both at mesoscale and submesoscale. We use the WAVEWATCH III framework to force wind waves in the eddy before and after instabilities occurred. Our findings show that the spatial variability of wave direction frequency and amplitude is very sensitive to the presence of underlying submesoscale structures resulting from the eddy destabilisation. As the surface current vorticity, the intrinsic frequency of incident waves is key in the wave response of the current modulation. Our findings also suggest that surface current gradients can be retrieved thanks to wave height gradients at scale where traditional altimeter measurements fail.


Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Rashid Alavi ◽  
Wangde Dai ◽  
Robert A Kloner ◽  
Niema M Pahlevan

Introduction: Intrinsic Frequency (IF) method is a recently developed systems-based method that extracts dynamics information about left ventricle function (LV), arterial dynamics, and the LV-arterial coupling from arterial waveforms. We have recently shown (Alavi et al. Circulation, 140 (2019), A12573-A12573) that IF can detect occurrence of an acute myocardial infarction (MI) using a single carotid pressure waveform. Here, we propose that the myocardial infarct size (area of necrosis over total LV area) can be approximated using a hybrid IF-artificial neural network (ANN) method. Methods: The standard MI model was used in anesthetized Sprague Dawley rats (n=27). The proximal left coronary artery was occluded for 30 minutes to ensure necrosis followed by 3 hours of reperfusion. The left ventricle slices were incubated in triphenyl tetrazolium chloride (TTC) to distinguish the necrotic (white) and the non-necrotic (dark red) areas (Fig.1a), thereby obtaining the size of MI through histopathology. IF parameters were computed from random carotid pressure waveforms 2 hours after the reperfusion. A 3-layer ANN model (4 input, 5 hidden, and 1 output node) was applied on IFs from 22 rats to design the ANN (18 for training, 4 for validation). The model was then tested on 5 different rats with the same MI procedure described above. Results: The results showed a significant correlation (R=0.64, P<0.0005) between our IF-artificial intelligence (IF-AI) model and the infarct size. The correlation was especially strong (R=0.84, P<0.0001) without the two outliers shown in Fig.1b. Conclusions: Our results suggest that a hybrid IF-AI method can predict the anatomic infarct size from an arterial waveform without advanced imaging. This technique is clinically significant since infarct sizes are link to the survival and development of heart failure in MI patients, and IF parameters can be obtained noninvasively from carotid waveforms using arterial tonometry devices or an iPhone.


Author(s):  
Ping Wang ◽  
Jun Lu ◽  
Caiyou Zhao ◽  
Mingming Chen ◽  
Mengting Xing

To analyze the reasons for rail clip fracture, the characteristics of rail corrugation were first measured using a rail corrugation meter. The vibration acceleration of the fastener clips at the sections with/without rail corrugation was measured, and the effects of rail corrugation on the clip vibration were analyzed. After this, a vehicle--track coupling dynamic model and a refined model for the fastener system were established in order to study the effects of rail corrugation on the vibration acceleration and stress on critical points. Finally, the rail grinding limits were determined based on the fatigue analysis method and the damage accumulation theory from the aspect of the fatigue life of the clip. The results of the study showed that the main wavelength of rail corrugation at the rail clip fracture section was approximately 40 mm. The vibration acceleration of the clip caused by rail corrugation was too large. Under normal installation conditions, the maximum clip stress was 1490 MPa at the small circular arc on the rear arch, which was identical to the on-site fracture location. The intrinsic frequency of the clip was approximately 810 Hz. Rail corrugation excited and triggered the forced vibration of the clip, and induced resonance at a speed of 120 km/h and a wavelength of 40 mm. The large cyclic stress amplitude of the clip with rail corrugation increased from 44 MPa to 68 MPa when compared with the clip without rail corrugation. Rail clip fracture was caused by the naturally occurring resonance fatigue arising from rail corrugation. For metro lines designed with a maximum speed of 120 km/h, it was suggested to control the rail corrugation amplitudes with a wavelength of 40 mm, 50 mm, 30 mm, 120 mm and 160 mm to below 0.04, 0.08, 0.16, 0.19 and 0.2 mm, respectively, taking into account the fatigue life of the clip.


2020 ◽  
Vol 50 (5) ◽  
pp. 1121-1135 ◽  
Author(s):  
Arnaud Le Boyer ◽  
Matthew H. Alford ◽  
Robert Pinkel ◽  
Tyler D. Hennon ◽  
Yiing J. Yang ◽  
...  

AbstractDespite sufficient wind forcing, internal waves in the South China Sea do not exhibit the strong near-inertial wave (NIW) peak that is typical in most of the world oceans. Using data from 10 contemporaneous moorings deployed in summer 2011, we show that strong isopycnal vertical tidal displacements transfer most of the near-inertial (NI) kinetic energy (KE) to frequencies higher than the inertial frequency in an Eulerian reference frame. Transforming to an isopycnal-following reference frame increases the KE at NI frequencies, suggesting the presence of NIWs. However, the projection onto a semi-Lagrangian coordinate system still underestimates the expected NI peak. To fully resolve NIWs requires the use of time-dependent vertical wavenumber–frequency spectra because the intrinsic frequency of the NIWs varies substantially, owing to Doppler shifting by lateral mesoscale flows. Here, we show NIW intrinsic frequency variations of ±0.2 cpd within few days, of similar magnitude as the observed variations of relative vorticity associated with the meandering Kuroshio.


2020 ◽  
Author(s):  
Peter Preusse ◽  
Markus Geldenhuys ◽  
Manfred Ern

&lt;p&gt;The acceleration of the large scale circulation by gravity wave is commonly described via the vertical gradient of the vertical flux of horizontal pseudomomentum, or in short of the momentum flux. The momentum flux vector is given by&lt;/p&gt;&lt;p&gt;&amp;#160;(F&lt;sub&gt;px&lt;/sub&gt;,F&lt;sub&gt;py&lt;/sub&gt;) = (1-f&lt;sup&gt;2&lt;/sup&gt;/&amp;#969;&lt;sup&gt;2&lt;/sup&gt;) ( &lt;u'w'&gt;,&lt;v'w'&gt;)&lt;/p&gt;&lt;p&gt;where &lt; &gt; describes the spatial or temporal mean of at least one wavelength or period of the gravity wave. If one is going actually to calculate momentum flux from an observation or high-resolution model, several difficulties arise. First, one has to know the intrinsic frequency &amp;#969; of the wave, second one tacitly assumes that only a single wave is causing the wind perturbations u', v' and w', and third one needs to find an appropriate averaging interval. One possibility to solve this is to perform spectral analysis. An alternative was introduced by Geller et al. (2013) which, based on the polarization relations, infers &amp;#969; directly from the perturbation wind temperature quadratics and is hence referred to as WTQ. In a brief study we will investigate the implication of the single wave assumption for the momentum flux calculated from data sets calculating multiple waves.&lt;/p&gt;


2020 ◽  
Author(s):  
Aurélien Podglajen ◽  
Albert Hertzog ◽  
Riwal Plougonven ◽  
Bernard Legras

Abstract. Due to their increasing spatial resolution, numerical weather prediction (NWP) models and the associated analyses resolve a growing fraction of the gravity wave (GW) spectrum. However, it is unclear how well this resolved part of the spectrum actually compares to the actual atmospheric variability. In particular, the Lagrangian variability, relevant, e.g., to atmospheric dispersion and to microphysical modeling in the Upper Troposphere-Lower Stratosphere (UTLS), has not yet been documented in recent products. To address this shortcoming, this paper presents an assessment of the GW spectrum as a function of the intrinsic (air parcel following) frequency in recent (re)analyses (ERA-interim, ERA5, the ECMWF operational analysis, MERRA-2 and JRA-55). Long-duration, quasi-Lagrangian balloon observations in the equatorial and Antarctic lower stratosphere are used as a reference for the atmospheric spectrum and compared to synthetic balloon observations along trajectories calculated using the wind and temperature fields of the reanalyses. Overall, the reanalyses represent realistic features of the spectrum, notably the spectral gap between planetary and gravity waves and a peak in horizontal kinetic energy associated with inertial waves near f in the polar region. In the tropics, they represent the slope of the spectrum at low frequency. However, the variability is generally underestimated, even in the low-frequency portion of the spectrum. In particular, the near-inertial peak, although present in the reanalyses, has a much reduced magnitude compared to balloon observations. We compare the variability of temperature, momentum flux and vertical wind speed, which are related to low, mid and high frequency waves, respectively. The distributions (PDFs) have similar shapes, but show increasing disagreement with increasing intrinsic frequency. Since at those altitudes they are mainly caused by gravity waves, we also compare the geographic distribution of vertical wind fluctuations in the different products, which emphasizes the increase of both GW variance and intermittency with horizontal resolution. Finally, we quantify the fraction of resolved variability and its dependency on model resolution for the different variables. In all (re)analyses products, a significant part of the variability is still missing and should hence be parameterized, in particular at high intrinsic frequency. Among the two polar balloon datasets used, one was broadcast on the global telecommunication system for assimilation in analyses while the other is made of independent observations (unassimilated in the reanalyses). Comparing the Lagrangian spectra between the two campaigns shows that they are largely influenced by balloon data assimilation, which especially enhances the variance at low frequency.


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