Velocity Variables Research Articles

Large‐scale asymptotics of velocity‐jump processes and nonlocal Hamilton–Jacobi equations

AbstractWe investigate a simple velocity jump process in the regime of large deviation asymptotics. New velocities are taken randomly at a constant, large, rate from a Gaussian distribution with vanishing variance. The Kolmogorov forward equation associated with this process is the linear BGK kinetic transport equation. We derive a new type of Hamilton–Jacobi equation which is nonlocal with respect to the velocity variable. We introduce a suitable notion of viscosity solution, and we prove well‐posedness in the viscosity sense. We also prove convergence of the logarithmic transformation toward this limit problem. Furthermore, we identify the variational formulation of the solution by means of an action functional supported on piecewise linear curves. As an application of this theory, we compute the exact rate of acceleration in a kinetic version of the celebrated F–KPP equation in the one‐dimensional case.

Wind-induced switch of estuarine residual circulations and sediment transport in microtidal bay

To reveal the mechanism for the transport of water and suspended sediments by wind-induced estuarine residual circulations, in situ moorings of acoustic Doppler current profilers were conducted in microtidal Onsan Bay. Water circulation within the bay was characterized by freshwater discharge from the river and free exchange with the open sea, showing current seaward outflow and landward inflow in the western (M1) and eastern (M2) flanks of the navigation channel, respectively. This circulation was influenced by the intrusion of alongshore currents strengthened (weakened) by the northerly (southerly) winds. In M1, seaward outflow was dominant, except for surface disturbances caused by winds. Meanwhile, the classical estuarine circulation (72% of the entire period) in M2, which prevailed under the southerly winds, was switched into the reversed estuarine circulation when the stress of the northerly wind persistently exceeded 0.005 Pa (> 5 h). The water transport (Trw) in M1 did not significantly vary depending on the wind direction, but the Trw in M2 could be reduced by 53% within 10 m above the bed as the southerly winds were transited into northerly winds. Over the entire period, Trw tended to be mutually compensated for and balanced by the circulation system between M1 and M2. On average, however, the sediment transport (Trsed) in M2 was 37% higher than M1, indicating that the suspended sediments were preferentially deposited within the bay. Most of the suspended sediments causing the deposition within the bay were mainly transported by estuarine residual circulation rather than tidal pumping. In M2, the frequent resuspension events of the fine-grained sediments (d50 = 6 μm) due to the high variability of the along-channel current velocity could maintain a sediment concentration of 18 mg l−1 in the bottom layer. These suspended sediments responded mainly to landward current in bottom layer (classical estuarine circulation) rather than seaward current (reversed estuarine circulation), contributing to increase in Trsed. Considering that the prevailing winds from 2013 to 2020 in Onsan Bay mainly create a favorable condition for the development of the classical estuarine circulation, the sedimentation is expected to persist.

RESPIRATORY VARIABILITY OF VALVULAR PEAK SYSTOLIC VELOCITY AS A NEW INDICATOR OF FLUID RESPONSIVENESS IN PATIENTS WITH SEPTIC SHOCK.

Objective: The aim of this study was to evaluate the reliability and feasibility of pulse Doppler measurements of peak velocity respiratory variability of mitral and tricuspid valve rings during systole as new dynamic indicators of fluid responsiveness in patients with septic shock. Methods: Transthoracic echocardiography (TTE) was performed to measure the respiratory variability of aortic velocity-time integral (∆VTI), respiratory variability of tricuspid annulus systolic peak velocity (∆RVS), respiratory variability of mitral annulus systolic peak velocity (∆LVS), and other related indicators. Fluid responsiveness was defined as a 10% increase in cardiac output after fluid expansion, assessed by TTE. Results: A total of 33 patients with septic shock were enrolled in this study. First, there was no significant difference in the population characteristics between the fluid responsiveness positive group (n = 17) and the fluid responsiveness negative group (n = 16) ( P > 0.05). Second, Pearson correlation test showed that ∆RVS, ∆LVS, and TAPSE with the relative increase in cardiac output after fluid expansion ( R = 0.55, P = 0.001; R = 0.40, P = 0.02; R = 0.36, P = 0.041). Third, multiple logistic regression analysis demonstrated that ∆RVS, ∆LVS, and TAPSE were significantly correlated with fluid responsiveness in patients with septic shock. Fourth, receiver operating characteristic (ROC) curve analysis revealed that ∆VTI, ∆LVS, ∆RVS, and TAPSE had good predictive ability for fluid responsiveness in patients with septic shock. The area under the curve (AUC) of ∆VTI, ∆LVS, ∆RVS, and TAPSE for predicting fluid responsiveness was 0.952, 0.802, 0.822, and 0.713, respectively. The sensitivity (Se) values were 1.00, 0.73, 0.81, and 0.83, whereas the specificity (Sp) values were 0.84, 0.91, 0.76, and 0.67, respectively. The optimal thresholds were 0.128, 0.129, 0.130, and 13.9 mm, respectively. Conclusion: Tissue Doppler ultrasound evaluation of respiratory variability of mitral and tricuspid annular peak systolic velocity could be a feasible and reliable method for the simple assessment of fluid responsiveness in patients with septic shock.

How Does Thermal Pressurization of Pore Fluids Affect 3D Strike-Slip Earthquake Dynamics and Ground Motions?

ABSTRACT Frictional heating during earthquake rupture raises the fault-zone fluid pressure, which affects dynamic rupture and seismic radiation. Here, we investigate two key parameters governing thermal pressurization of pore fluids – hydraulic diffusivity and shear-zone half-width – and their effects on earthquake rupture dynamics, kinematic source properties, and ground motions. We conduct 3D strike-slip dynamic rupture simulations assuming a rate-and-state dependent friction law with strong velocity weakening coupled to thermal-pressurization of pore fluids. Dynamic rupture evolution and ground shaking are densely evaluated across the fault and Earth’s surface to analyze the variations of rupture parameters (slip, peak slip rate, rupture speed, and rise time), correlations among rupture parameters, and variability of peak ground velocity. Our simulations reveal how variations in thermal-pressurization affect earthquake rupture properties. We find that the mean slip and rise time decrease with increasing hydraulic diffusivity, whereas mean rupture speed and peak slip-rate remain almost constant. Mean slip, peak slip-rate, and rupture speed decrease with increasing shear-zone half-width, whereas mean rise time increases. Shear-zone half-width distinctly affects the correlation between rupture parameters, especially for parameter pairs (slip, rupture speed), (peak slip-rate, rupture speed), and (rupture speed, rise time). Hydraulic diffusivity has negligible effects on these correlations. Variations in shear-zone half-width primarily impact rupture speed, which then may affect other rupture parameters. We find a negative correlation between slip and peak slip-rate, unlike simpler dynamic rupture models. Mean peak ground velocities decrease faster with increasing shear-zone half-width than with increasing hydraulic diffusivity, whereas ground-motion variability is similarly affected by both the parameters. Our results show that shear-zone half-width affects rupture dynamics, kinematic rupture properties, and ground shaking more strongly than hydraulic diffusivity. We interpret the importance of shear-zone half-width based on the characteristic time of diffusion. Our findings may inform pseudodynamic rupture generators and guide future studies on how to account for thermal-pressurization effects.

Enhancing Feature Extraction through G-PLSGLR by Decreasing Dimensionality of Textual Data

The technology of big data has become highly popular in numerous industries owing to its various characteristics such as high value, large volume, rapid velocity, wide variety, and significant variability. Nevertheless, big data presents several difficulties that must be addressed, including lengthy processing times, high computational complexity, imprecise features, significant sparsity, irrelevant terms, redundancy, and noise, all of which can have an adverse effect on the performance of feature extraction. The objective of this research is to tackle these issues by utilizing the Partial Least Square Generalized Linear Regression (G-PLSGLR) approach to decrease the high dimensionality of text data. The suggested algorithm is made up of four stages: Firstly, gathering featured data in vector space model (VSM) and training it with bootstrap technique. Second, grouping trained feature samples using a Pearson correlation coefficient and graph-based technique. Third, getting rid of unimportant features by ranking significant group features using PLSGR. Lastly, choosing or extracting significant features using Bayesian information criterion (BIC). The G-PLSGLR algorithm surpasses current methods by achieving a high reduction rate and classification performance, while minimizing feature redundancy, time consumption, and complexity. Furthermore, it enhances the accuracy of features by 35%.

Spatio-Temporal Gait Parameters to Distinguish Multiple Sclerosis Disability during Dual- Task Walk

Background Differences in gait between people with multiple sclerosis (PwMS) and controls are well documented and effective in distinguishing between disability levels based on the Expanded Disability Severity Scale (EDSS) during preferred walking (PrW). However, clinically measured PrW does not consider higher cognitive demand required to perform more complex motor tasks in everyday living (e.g., conversing while walking). A dual-task walk (DTW) mimics this cognitive load, thus offering greater ecological validity when distinguishing between disability levels in PwMS. Purpose To evaluate the utility of spatio-temporal gait parameters during a DTW to distinguish between mild and moderate disability in PwMS. Methods Gait velocity, stride velocity, step width, step length and mean gait variability index were measured in a convenience sample of 44 PwMS (36=mild MS: EDSS 0 to 3.5, 7=moderate MS: EDSS 4.0 to 6.0) during PrW and DTW using a Protokinetic Zeno Walkway. Subjects were dichotomized into mild or moderate disability groups. Variable selection was performed using stepwise linear regression, including all gait metrics and covariates (sex, age, height, type of multiple sclerosis: relapsing or progressive, and disease duration). Logistic regressions were performed separately for PrW and DTW. Results During PrW, greater step length (cm) was associated with mild disability (R^2=0.39, ChiSquare=14.72, p<0.001). During DTW, both stride width (ChiSquare=4.69, p=0.03) and step length (ChiSquare=5.16, p=0.02) were associated with disability (R^2=0.38): people with moderate disability demonstrated increased step width and decreased step length. Discussion Results highlight the need to investigate differences in gait during DTW in addition to PrW in PwMS with different disability levels. However, generalizability is limited due to disproportionate sample sizes of disability groups. Still, DTW protocols may provide supplemental information for monitoring disability among PwMS, which can inform clinicians of the effectiveness of gait interventions or disease progression. Differences in gait between people with multiple sclerosis (PwMS) and controls are well documented and effective in distinguishing between disability levels based on the Expanded Disability Severity Scale (EDSS) during preferred walking (PrW). However, clinically measured PrW does not consider higher cognitive demand required to perform more complex motor tasks in everyday living (e.g., conversing while walking). A dual-task walk (DTW) mimics this cognitive load, thus offering greater ecological validity when distinguishing between disability levels in PwMS. To evaluate the utility of spatio-temporal gait parameters during a DTW to distinguish between mild and moderate disability in PwMS. Gait velocity, stride velocity, step width, step length and mean gait variability index were measured in a convenience sample of 44 PwMS (36=mild MS: EDSS 0 to 3.5, 7=moderate MS: EDSS 4.0 to 6.0) during PrW and DTW using a Protokinetic Zeno Walkway. Subjects were dichotomized into mild or moderate disability groups. Variable selection was performed using stepwise linear regression, including all gait metrics and covariates (sex, age, height, type of multiple sclerosis: relapsing or progressive, and disease duration). Logistic regressions were performed separately for PrW and DTW. During PrW, greater step length (cm) was associated with mild disability (R^2=0.39, ChiSquare=14.72, p<0.001). During DTW, both stride width (ChiSquare=4.69, p=0.03) and step length (ChiSquare=5.16, p=0.02) were associated with disability (R^2=0.38): people with moderate disability demonstrated increased step width and decreased step length. Results highlight the need to investigate differences in gait during DTW in addition to PrW in PwMS with different disability levels. However, generalizability is limited due to disproportionate sample sizes of disability groups. Still, DTW protocols may provide supplemental information for monitoring disability among PwMS, which can inform clinicians of the effectiveness of gait interventions or disease progression.

Paradoxical Associations of Occupational and Nonoccupational Sedentary Behavior With Cardiovascular Disease Risk Measures in Desk Workers.

We assessed sedentary behavior (SB) patterns and examined its associations, by domain, with cardiovascular disease (CVD) risk measures in desk workers ( N = 273). Sedentary behavior was measured by activPAL3 and partitioned into occupational and nonoccupational SB. Cardiovascular disease risk measures included blood pressure, pulse wave velocity, heart rate, and heart rate variability. Paired t tests evaluated patterns of SB across domains. Linear regressions estimated associations of occupational and nonoccupational SB with CVD risk measures. Participants spent 69% of their time in SB; higher proportions were accumulated during occupational versus nonoccupational time. Higher all-domain SB was only associated with higher pulse wave velocity. Paradoxically, greater nonoccupational SB unfavorably associated with CVD risk measures, while higher occupational SB favorably correlated to CVD risk measures. Observed paradoxical associations suggest that domain should be considered in efforts to improve cardiovascular health by reducing SB.

A New Immersed Finite Element Method for Two-Phase Stokes Problems Having Discontinuous Pressure

Abstract In this paper, we develop a new immersed finite element method (IFEM) for two-phase incompressible Stokes flows. We allow the interface to cut the finite elements. On the noninterface element, the standard Crouzeix–Raviart element and the P 0 {P_{0}} element pair is used. On the interface element, the basis functions developed for scalar interface problems (Kwak et al., An analysis of a broken P 1 {P_{1}} -nonconforming finite element method for interface problems, SIAM J. Numer. Anal. (2010)) are modified in such a way that the coupling between the velocity and pressure variable is different. There are two kinds of basis functions. The first kind of basis satisfies the Laplace–Young condition under the assumption of the continuity of the pressure variable. In the second kind, the velocity is of bubble type and is coupled with the discontinuous pressure, still satisfying the Laplace–Young condition. We remark that in the second kind the pressure variable has two degrees of freedom on each interface element. Therefore, our methods can handle the discontinuous pressure case. Numerical results including the case of the discontinuous pressure variable are provided. We see optimal convergence orders for all examples.

Evaluation of the potential stranding risk for aquatic organisms according to long-term morphological changes and grain size in alpine rivers impacted by hydropeaking

Hydropeaking is one of the major hydropower-related disturbances of natural processes in river systems. The artificial flow fluctuations that are caused by the on-demand production of electricity are known for their severe impacts on aquatic ecosystems. These particularly affect those species and life stages that are not able to adjust their habitat selection to rapid up- and downramping rates. To date, the stranding risk has both experimentally and numerically mainly been investigated with variable hydropeaking graphs over stable river bathymetries. There is a lack of knowledge on how single, discrete peaking events vary concerning their impact on the stranding risk when the river morphology changes in the long-term perspective. The present study precisely addresses this knowledge gap by investigating morphological changes on the reach scale over a period of 20 years and the related variability of the lateral ramping velocity as a proxy for stranding risk. Two alpine gravel bed rivers impacted by hydropeaking over decades were tested by applying a one-dimensional and two-dimensional unsteady modelling approach. Both the Bregenzerach River and the Inn River exhibit alternating gravel bars on the reach scale. The results of the morphological development, however, showed different developments in the period 1995–2015. The Bregenzerach River displayed continuous aggradation (uplift of river bed) over the various selected submonitoring periods. In contrast, the Inn River showed continuous incision (erosion of river bed). The stranding risk exhibited high variability on a single cross-sectional basis. However, on the reach scale, no significant changes in stranding risk were calculated for either river reach. In addition, the impacts of river incision on the substrate composition were investigated. Here, in line with preceding studies, the results show that the coarsening of substrate increases the stranding risk and that especially the d90 (90 % finer of the grain size distribution) must be considered. The present study reveals that the quantified stranding risk of aquatic organisms is a function of the general morphological (bar) characteristics of the impacted river and both the morphological and grain size development have an impact on the potential stranding risk of aquatic organisms and should be considered in the revision of licences in the management of multi-stressed river systems.

Homogenization of the linear Boltzmann equation with a highly oscillating scattering term in extended phase space

In this article, we rigorously prove the homogenization limit of the linear Boltzmann equation when the scattering term is highly oscillating with respect to the velocity variable. We prove that the limit equation keeps, in a suitably extended phase space, the same structure as the non-homogenized one. This situation does not coincide with what happens in standard phase space, where the appearance of memory terms is expected.

Velocity-Based Method in Free-Weight and Machine-Based Training Modalities: The Degree of Freedom Matters.

Hernández-Belmonte, A, Buendía-Romero, Á, Pallares, JG, and Martínez-Cava, A. Velocity-based method in free-weight and machine-based training modalities: the degree of freedom matters. J Strength Cond Res 37(9): e500-e509, 2023-This study aimed to analyze and compare the load-velocity relationships of free-weight and machine-based modalities of 4 resistance exercises. Moreover, we examined the influence of the subject's strength level on these load-velocity relationships. Fifty men completed a loading test in the free-weight and machine-based modalities of the bench press, full squat, shoulder press, and prone bench pull exercises. General and individual relationships between relative intensity (%1RM) and velocity variables were studied through the coefficient of determination ( R2 ) and standard error of the estimate ( SEE ). Moreover, the velocity attained to each %1RM was compared between both modalities. Subjects were divided into stronger and weaker to study whether the subject's strength level influences the mean test (mean propulsive velocity [MPV Test ]) and 1RM (MPV 1RM ) velocities. For both modalities, very close relationships ( R2 ≥ 0.95) and reduced estimation errors were found when velocity was analyzed as a dependent ( SEE ≤ 0.086 m·s -1 ) and independent ( SEE ≤ 5.7% 1RM) variable concerning the %1RM. Fits were found to be higher ( R2 ≥ 0.995) for individual load-velocity relationships. Concerning the between-modality comparison, the velocity attained at each intensity (from 30 to 100% 1RM) was significantly faster for the free-weight variant. Finally, nonsignificant differences were found when comparing MPV Test (differences ≤ 0.02 m·s -1 ) and MPV 1RM (differences ≤ 0.01 m·s -1 ) between stronger and weaker subjects. These findings prove the accuracy and stability of the velocity-based method in the free-weight and machine-based variants but highlight the need to use the load-velocity relationship (preferably the individual one) specific to each training modality.

Efficient prediction of airborne noise propagation in a non-turbulent urban environment using Gaussian beam tracing method

This paper presents a noise propagation approach based on the Gaussian beam tracing (GBT) method that accounts for multiple reflections over three-dimensional terrain topology and atmospheric refraction due to horizontal and vertical variability in wind velocity. A semi-empirical formulation is derived to reduce truncation error in the beam summation for receivers on the terrain surfaces. The reliability of the present GBT approach is assessed with an acoustic solver based on the finite element method (FEM) solutions of the convected wave equation. The predicted wavefields with the two methods are compared for different source-receiver geometries, urban settings, and wind conditions. When the beam summation is performed without the empirical formulation, the maximum difference is more than 40 dB; it drops below 8 dB with the empirical formulation. In the presence of wind, the direct and reflected waves can have different ray paths than those in a quiescent atmosphere, which results in less apparent diffraction patterns. A 17-fold reduction in computation time is achieved compared to the FEM solver. The results suggest that the present GBT acoustic propagation model can be applied to high-frequency noise propagation in urban environments with acceptable accuracy and better computational efficiency than full-wave solutions.

The Variability and Radial Velocity of Planetary Nebula Central Stars

The extremely accurate estimates of stellar variability and radial velocity in the Gaia Data Release 3 (Gaia DR3) have enabled us to examine the close binarity and radial velocity (RV) of central stars (CSs) of planetary nebulae (PNe). This study is twofold: (1) searching for new close binary CS candidates to better understand how binarity affects the formation and evolution of PNe; and (2) extending the sample size of known RVs of PNe in order to understand their kinematics and the dynamics of the Milky Way. As a target sample, we used all true, possible, and likely PNe available in the literature. Then, we looked for their matched Gaia DR3 sources that provide measurements of variability and RV. As a result, we detected the first large collection of trustworthy photometric variability of 26 symbiotic stars and 82 CSs. In this CS group, there are 24 sources already classified as true close binary CSs in the literature. Hence, we discovered 58 new close binary CS candidates. This close binary (CB) sample represents more than half of what is currently available in the literature. In addition, we identified the radial velocities for 51 PNe. To our knowledge, 24 of these were measured for the first time. The RV measurements predicted by Gaia, based on the Doppler shift of the CS absorption lines, and those derived from nebular emission lines, show satisfactory agreement except for a few extremely high-velocity PNe.

Barcoding, linear and nonlinear analysis of full-day leg movements in infants with typical development and infants at risk of developmental disabilities: Cross-sectional study.

Traditional methods do not capture the multidimensional domains and dynamic nature of infant behavioral patterns. We aim to compare full-day, in-home leg movement data between infants with typical development (TD) and infants at risk of developmental disabilities (AR) using barcoding and nonlinear analysis. Eleven infants with TD (2-10 months) and nine infants AR (adjusted age: 2-14 months) wore a sensor on each ankle for 7 days. We calculated the standard deviation for linear variability and sample entropy (SampEn) of leg acceleration and angular velocity for nonlinear variability. Movements were also categorized into 16 barcoding states, and we calculated the SampEn and proportions of the barcoding. All variables were compared between the two groups using independent-samples t-test or Mann-Whitney U test. The AR group had larger linear variability compared to the TD group. SampEn was lower in the AR group compared to TD group for both acceleration and angular velocity. Two barcoding states' proportions were significantly different between the two groups. The results showed that nonlinear analysis and barcoding could be used to identify the difference of dynamic multidimensional movement patterns between infants AR and infants with TD. This information may help early diagnosis of developmental disabilities in the future.

The effect of a digital-assisted group rehabilitation on clinical and functional outcomes after total hip and knee arthroplasty—a prospective randomized controlled pilot study

BackgroundThe rising number of total hip and knee arthroplasties and the decreasing availability of physiotherapists require clinically and economically effective rehabilitation approaches. Therefore, the present pilot study investigated the effect of a novel digital-assisted individualized group rehabilitation program on clinical and functional outcomes after total hip and knee arthroplasty.MethodsIn this randomized controlled pilot study, 26 patients undergoing total knee or hip replacement were randomly assigned to either the intervention group (IG, novel digital-assisted group therapy) or the control group (CG, standard postoperative physiotherapy currently carried out in Germany). The IG received the novel digital-assisted group therapy twice per week for a six-months period, while the CG received individual outpatient therapy depending on the prescription of the supervising physician. The number of therapy sessions was recorded. Moreover, subjective outcomes (EuroQol-5Dimensions (EQ-5D) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)), functional outcome (30 s sit to stand test and timed up and go test (TUG)), as well as gait parameters were quantified preoperatively as well as at three and six months after surgery. Data were analyzed using an analysis of covariance with baseline-adjustment.ResultsNo patient-reported falls, pain, and hospital readmissions were recorded. On average, the IG received more therapy sessions. The clinical and functional outcomes were mainly not significantly different between groups at three- and six-months follow-up, but medium to large effect sizes for the differences in quality of life (EQ-5D) as well as pain, stiffness, and physical function (WOMAC), and TUG performance were observed in favor of the IG. However, the IG showed a higher variability of gait velocity after total joint replacement.ConclusionThe digital-assisted rehabilitation had positive effects on quality of life, pain, stiffness, physical function, and TUG performance. Nevertheless, the therapy concept may be improved by adding exercises focusing on gait performance to reduce gait variability. The results indicate that the digital-assisted therapy concept is effective and safe. Therefore, a consecutive full-scaled randomized controlled clinical trial is recommended.Trial registrationThis study was retrospectively registered on 14/02/2022 in the German Clinical Trial Register (DRKS00027960).

Adaptive fractional‐order nonsingular fast terminal sliding mode formation control of multiple quadrotor UAVs‐based distributed estimator

AbstractThis paper mainly solves two major problems that are unavoidable in leader–follower formation process of quadrotor UAV group: the existence of external uncertainty disturbance and communication limited between quadrotor unmanned aerial vehicle (UAV) group. To solve the problem that only one of the followers in the leader–follower formation can obtain the leader's information, an improved distributed estimator is proposed in this paper, which can accurately estimate the leader's information for each follower. In addition, in order to eliminate the influence of uncertain external disturbance on the performance of quadrotor UAV, an adaptive estimation law is designed based only on velocity and position variables. For the attitude and position subsystem of the quadrotor UAV, a sliding surface with fractional‐order term is designed. Which makes the quadrotor UAV tracking error system obtain good robustness at the stage of reaching the sliding surface and fast convergence and accurate tracking performance in the sliding stage. Based on Lyapunov stability theory, the convergence results are analyzed strictly. The results show that the algorithm can make the position distance between leader and followers converge to the desired offset. Simulation results verify the effectiveness and superiority of the control algorithm.

Application of Machine Learning Techniques to Ocean Mooring Time Series Data

Abstract In situ observations are vital to improving our understanding of the variability and dynamics of the ocean. A critical component of the ocean circulation is the strong, narrow, and highly variable western boundary currents. Ocean moorings that extend from the seafloor to the surface remain the most effective and efficient method to fully observe these currents. For various reasons, mooring instruments may not provide continuous records. Here we assess the application of the Iterative Completion Self-Organizing Maps (ITCOMPSOM) machine learning technique to fill observational data gaps in a 7.5 yr time series of the East Australian Current. The method was validated by withholding parts of fully known profiles, and reconstructing them. For 20% random withholding of known velocity data, validation statistics of the u- and υ-velocity components are R2 coefficients of 0.70 and 0.88 and root-mean-square errors of 0.038 and 0.064 m s−1, respectively. Withholding 100 days of known velocity profiles over a depth range between 60 and 700 m has mean profile residual differences between true and predicted u and υ velocity of 0.009 and 0.02 m s−1, respectively. The ITCOMPSOM also reproduces the known velocity variability. For 20% withholding of salinity and temperature data, root-mean-square errors of 0.04 and 0.38°C, respectively, are obtained. The ITCOMPSOM validation statistics are significantly better than those obtained when standard data filling methods are used. We suggest that machine learning techniques can be an appropriate method to fill missing data and enable production of observational-derived data products. Significance Statement Moored observational time series of ocean boundary currents monitor the full-depth variability and change of these dynamic currents and are used to understand their influence on large-scale ocean climate, regional shelf–coastal processes, extreme weather, and seasonal climate. In this study we apply a machine learning technique, Iterative Completion Self-Organizing Maps (ITCOMPSOM), to fill data gaps in a boundary current moored observational data record. The ITCOMPSOM provides an improved method to fill data gaps in the mooring record and if applied to other observational data records may improve the reconstruction of missing data. The derived gridded data product should improve the accessibility and potentially increase the use of these data.

Cerebral blood flow response to cardiorespiratory oscillations in healthy humans

Dynamic cerebral autoregulation (CA) characterizes the cerebral blood flow (CBF) response to abrupt changes in arterial blood pressure (ABP). CA operates at frequencies below 0.15Hz. ABP regulation and probably CA are modified by autonomic nervous activity. We investigated the CBF response and CA dynamics to mild increase in sympathetic activity. Twelve healthy volunteers underwent oscillatory lower body negative pressure (oLBNP), which induced respiratory-related ABP oscillations at an average of 0.22Hz. We recorded blood velocity in the internal carotid artery (ICA) by Doppler ultrasound and ABP. We quantified variability and peak wavelet power of ABP and ICA blood velocity by wavelet analysis at low frequency (LF, 0.05-0.15Hz) and Mayer waves (0.08-0.12Hz), respectively. CA was quantified by calculation of the wavelet synchronization gamma index for the pair ABP-ICA blood velocity in the LF and Mayer wave band. oLBNP increased ABP peak wavelet power at the Mayer wave frequency. At the Mayer wave, ABP peak wavelet power increased by >70% from rest to oLBNP (p<0.05), while ICA blood flow velocity peak wavelet power was unchanged, and gamma index increased (from 0.49 to 0.69, p<0.05). At LF, variability in both ABP and ICA blood velocity and gamma index were unchanged from rest to oLBNP. Despite an increased gamma index at Mayer wave, ICA blood flow variability was unchanged during increased ABP variability. The increased synchronization during oLBNP did not cause less stable CBF or less active CA. Sympathetic activation seems to improve the mechanisms of CA.

Predicting Convective Downdrafts From Updrafts and Environmental Conditions in a Global Storm Resolving Simulation

AbstractOne important component of precipitating convection is the formation of convective downdrafts. They can terminate the initial updraft, affect the mean properties of the boundary layer, and cause strong winds at the surface. While the basic forcing mechanisms for downdrafts are well understood, it is difficult to formulate general relationships between updrafts, environmental conditions, and downdrafts. To better understand what controls different downdraft properties, we analyze downdrafts over tropical oceans in a global storm resolving simulation. Using a global model allows us to examine a large number of downdrafts under naturally varying environmental conditions. We analyze the various factors affecting downdrafts using three alternative methods. First, hierarchical clustering is used to examine the correlation between different downdraft, updraft, and environmental variables. Then, either random forests or multiple linear regression are used to estimate the relationships between downdraft properties and the updraft and environmental predictors. We find that these approaches yield similar results. Around 75% of the variability in downdraft mass flux and 37% of the variability in downdraft velocity are predictable. Analyzing the relative importance of our various predictors, we find that downdrafts are coupled to updrafts via the precipitation generation argument. In particular, updraft properties determine rain amount and rate, which then largely control the downdraft mass flux and, albeit to a lesser extent, the downdraft velocity. Among the environmental variables considered, only lapse rate is a valuable predictor: a more unstable environment favors a higher downdraft mass flux and a higher downdraft velocity.

Scripps Argo Trajectory-Based Velocity Product: Global Estimates of Absolute Velocity Derived from Core, Biogeochemical, and Deep Argo Float Trajectories at Parking Depth

Abstract Global estimates of absolute velocities can be derived from Argo float trajectories during drift at parking depth. A new velocity dataset developed and maintained at Scripps Institution of Oceanography is presented based on all Core, Biogeochemical, and Deep Argo float trajectories collected between 2001 and 2020. Discrepancies between velocity estimates from the Scripps dataset and other existing products including YoMaHa and ANDRO are associated with quality control criteria, as well as selected parking depth and cycle time. In the Scripps product, over 1.3 million velocity estimates are used to reconstruct a time-mean velocity field for the 800–1200 dbar layer at 1° horizontal resolution. This dataset provides a benchmark to evaluate the veracity of the BRAN2020 reanalysis in representing the observed variability of absolute velocities and offers a compelling opportunity for improved characterization and representation in forecast and reanalysis systems. Significance Statement The aim of this study is to provide observation-based estimates of the large-scale, subsurface ocean circulation. We exploit the drift of autonomous profiling floats to carefully isolate the inferred circulation at the parking depth, and combine observations from over 11 000 floats, sampling between 2001 and 2020, to deliver a new dataset with unprecedented accuracy. The new estimates of subsurface currents are suitable for assessing global models, reanalyses, and forecasts, and for constraining ocean circulation in data-assimilating models.