Velocity Traces Research Articles

421 Exploring hypertensive patient profiles based on full myocardial deformation and Doppler traces - insights from a machine-learning approach

Abstract Funding Acknowledgements Horizon 2020 European Commission Project H2020-MSCA-ITN-2016 (764738), Grant from Fundacio La Marató de TV3 (040310) Background and aim Contemporary echocardiography provides complex data on cardiac function contained in both blood-pool and tissue deformation traces. Their current interpretation relies on clinical experience and selected peak or averaged velocity values, which might not capture the complexity throughout the cardiac cycle. The aim is to investigate if machine learning could recognize relevant patient profiles in arterial hypertension by integrating all echocardiographic data to better define potential pathophysiological changes in left ventricle (LV) remodeling. Methods An echocardiogram was performed in 100 patients with established arterial hypertension (> 3 years). Myocardial deformation traces of the LV and the left atrium (LA), assessed by 2D speckle tracking, the aortic outflow Doppler trace, the lateral and septal mitral annular Doppler velocity traces, and the mitral inflow Doppler trace were assessed as measures of cardiac function. An unsupervised machine learning algorithm (multiple kernel learning) was used to reduce the dimensionality of these data, and to position the patients based on the similarities of echocardiographic data. The main patterns of variability present in the data were interpreted through non-linear regression analysis. Classic echocardiographic parameters, measured by a clinician, were then compared between the intermediate and extreme patient profiles across the variability spectrum. Results Figure 1 shows differences in velocity and deformation traces between the three representative patient profiles. While at one end of the spectrum, all echocardiographic traces were normal (red and green), the data of the other extreme patient profile (blue) describes a characteristic and consistent LV pressure overload remodeling pattern, with slightly reduced and delayed aortic outflow velocities, fused E and A waves with the ratio < 1, lower e’ mitral annulus velocities, decreased basal septal strain with post-systolic motion, prolonged relaxation in early diastole as seen by the deformation traces, and a change in atrial deformation dynamic with augmentation of LA contractile strain. The clinical measurements concurred with the remodeling profile describing smaller end-diastolic LV diameter and end-systolic and end-diastolic LV volumes, a reduced E/A ratio and e’ medial annular velocity, reduced TAPSE and increased LA contractile strain. Conclusion Machine learning based assessment of complex echocardiographic data has the potential to recognize an integrated and comprehensive patient profile related to LV remodeling within the hypertensive cohort without relying on classical clinical measurements and parameters, but by learning from subtle differences globally present in velocity and deformation echocardiographic data. Abstract 421 Figure 1

P768 Potential utility of fully automated Doppler flow velocity tracing software in patients with atrial fibrillation

Abstract Background Stroke volume (SV) using Doppler echocardiography is a significant prognosticator in patients with atrial fibrillation (AF). However, tracing multiple left ventricular outflow tract (LVOT) Doppler flow velocity envelope is tedious. Although ASE recommends to average 5 -10 beats of SV in AF, this has not been validated. Recently developed fully automated Doppler flow velocity analytical software can analyze Doppler parameters in multiple consecutive beats on the screen within a few seconds. Purpose We aimed to determine the usefulness of the software, and to validate the minimum number of beats required to approximate SV in patients with AF. Methods We selected 21 AF patients who had undergone 2D echocardiography using GE ultrasound machine (E95, GE healthcare). LVOT area was calculated by 3.14×(LVOT diameter/2)². LVOT pulse-wave Doppler velocity was recorded from an apical approach with a quiet breathing. To maximize the number of flow envelope on the screen, sweep speed was set at 12.5 mm/s. LVOT velocity time integral was measured by both manual tracing method and fully automated method (Cardiac Auto Doppler, GE healthcare). The grand truth of mean SV (reference SV) in each patient was defined as the averaged values of SV from all consecutive beats. We also calculated the mean SV value with the successive addition of sequential beats started from the 1st beat. Each value was compared with the reference SV and % variability was calculated. We determined the minimum number of beats showing %variability becoming <5%. Results Mean age was 77 years. Mean heart rate and reference SV index (SVI) were 80 ± 12 bpm and 35 ± 10 mL/m2. A total number of beats for recording was ranged from 16 to 25 in each patient. The fully automated software could analyze Doppler envelope in 395 out of 412 beats (Feasibility: 96%). Although there was a good correlation of SV in individual beats between the manual and automatic method (r = 0.92), the automatic method significantly overestimated SV (mean bias: 2.6 mL, p < 0.001) compared with the manual method. The median values of minimum number of beats showing % variability < 5% were 4 (interquartile range: 2 -7) for manual tracing method. The corresponding values were 5 (2 -6) for automatic method. If we used mean values of SV during consecutive 10 beats, 92% of patients using manual method and 96% of patients using automatic method showed % variability < 5%. There were excellent correlation between reference SV and averaged SV from the 1st beat to 10th beat (manual: r = 0.98, automatic: r = 0.99). If we defined low flow status as < 35 mL/m2, averaged SVI during consecutive 10 beats using the automatic method had a correct diagnosis in 20 out of 21 patients. Conclusions We concluded that minimum number of required beats for averaging was 10 in most AF patients. Rapid and reliable SV analysis with a novel fully automated Doppler software has a potential for its adoption in busy echocardiography laboratories.

Analysis of nonstandardized stress echocardiography sequences using multiview dimensionality reduction.

Alternative stress echocardiography protocols such as handgrip exercise are potentially more favorable towards large-scale screening scenarios than those currently adopted in clinical practice. However, these are still underexplored because the maximal exercise levels are not easily quantified and regulated, requiring the analysis of the complete data sequences (thousands of images), which represents a challenging task for the clinician. We propose a framework for the analysis of these complex datasets, and illustrate it on a handgrip exercise dataset including complete acquisitions of 10 healthy controls and 5 ANT1 mutation patients (1377 cardiac cycles). The framework is based on an unsupervised formulation of multiple kernel learning, which is used to integrate information coming from myocardial velocity traces and heart rate to obtain a lower-dimensional representation of the data. Such simplified representation is then explored to discriminate groups of response and understand the underlying pathophysiological mechanisms. The analysis pipeline involves the reconstruction of population-specific signatures using multiscale kernel regression, and the clustering of subjects based on the trajectories defined by their projected sequences. The results confirm that the proposed framework is able to detect distinctive clusters of response and to provide insight regarding the underlying pathophysiology.

Stochastic multiscale flux basis for Stokes-Darcy flows

Three algorithms are developed for uncertainty quantification in modeling coupled Stokes and Darcy flows. The porous media may consist of multiple regions with different properties. The permeability is modeled as a non-stationary stochastic variable, with its log represented as a sum of local Karhunen-Loève (KL) expansions. The problem is approximated by stochastic collocation on either tensor-product or sparse grids, coupled with a multiscale mortar mixed finite element method for the spatial discretization. A non-overlapping domain decomposition algorithm reduces the global problem to a coarse scale mortar interface problem, which is solved by an iterative solver, for each stochastic realization. In the traditional domain decomposition implementation, each subdomain solves a local Dirichlet or Neumann problem in every interface iteration. To reduce this cost, two additional algorithms based on deterministic or stochastic multiscale flux basis are introduced. The basis consists of the local flux (or velocity trace) responses from each mortar degree of freedom. It is computed for each subdomain independently before the interface iteration begins. The use of the multiscale flux basis avoids the need for subdomain solves on each iteration. The deterministic basis is computed at each stochastic collocation and used only at this realization. The stochastic basis is formed by further looping over all local realizations of a subdomain's KL region before the stochastic collocation begins. It is reused over multiple realizations. Numerical tests are presented to illustrate the performance of the three algorithms, with the stochastic multiscale flux basis showing significant savings in computational cost compared to the other two algorithms.

Major Parameters Affect the Non-Liner Response of Structure Under Near-Fault Earthquakes

Near-fault ground motion can be identified by the presence of a predominant long duration pulse in the velocity traces mainly due to directivity effect. This pulse exposes the structure to high input energy at the beginning of the earthquake which leads to a higher response in comparison with the ordinary ground motions. This paper investigates 79 earthquake records with different properties to achieve three goals: the first aim is to compare between the linear and nonlinear response of SDOF systems under near-fault and far-fault earthquakes. While the second objective is to examine the parameters that control the characteristics of near-fault earthquakes. Two factors have been studied which is PGV/PGA ratio and pulse period. Finally, the seismic code provisions related to the near-fault earthquakes were evaluated in term of the elastic acceleration response spectrum, the evaluation is adopted for American Society of Civil Engineers code ASCE 7 and Uniform Building Code UBC. The results lead to the following conclusions: with respect to a specific PGA, the near-fault earthquake imposed higher response in comparison with far-field earthquakes. The near-fault earthquakes become severe as the PGV/PGA and pulse period increase. The interested seismic codes can cover the actual behavior based on the average response of a certain amount of data, while it may become non-conservative relative to an individual record.

Analysis of Flow Field Characteristics of Unequal Distance Fans

This paper establishes the simulation model of the unequal-distance fan, obtains the details of the flow field when the fan works by CFD simulation method, and analyses the internal flow field characteristics of the unequal-distance fan from three aspects: streamline trace distribution, pressure distribution and velocity distribution, so as to get the working condition of the fan, which is of great significance for the design and transformation of the fan structure.

Variable step-size incremental conductance method used in PV power system

The paper presents a new control strategy on MPPT as a result of the disadvantages of the present variable step-size incremental conductance method on MPPT, which is simulated in MATLAB/Simulink. The simulation results show that the new control strategy is obviously better than the previous in terms of the tracing velocity, which is the expected result.

Observational Signatures of End-dominated Collapse in the S242 Filamentary Structure

Abstract We present new CO (13CO(1–0) and C18O(1–0)) and CS(2–1) line observations of an elongated filamentary structure (length ∼30 pc) in the star-forming site S242, which were taken with the OSO-20 m telescope. One filament’s end hosts the S242 H ii region, while the other end contains Planck cold clumps. Several subregions are identified in the filament, and are supersonic with Mach number of 2.7–4.0. The study of the dynamical states shows supercritical nature of the subregions (except the central part), which could not be supported by a combination of thermal and turbulent motions. Young stellar objects are seen toward the entire filament, but are more concentrated toward its ends. Dense molecular cores are observed mainly toward the filament ends, and are close to virial equilibrium. Position–velocity plots trace velocity gradients (∼1 km s−1 pc−1) toward both ends. An oscillatory pattern in velocity is also observed toward the filament, indicating its fragmentation. The collapse timescale of the filament is computed to be ∼3.5 Myr. Using the 13CO data, the structure function in velocity of the filament is found to be very similar as that seen in the Musca cloud for lags ∼1–3 pc, and deviates from the Larson’s velocity–size relationship. The observed oscillatory pattern in the structure function at higher lags suggests the existence of large-scale and ordered velocity gradients, as well as the fragmentation process through accretion along the filament. Considering all the observed results along with their uncertainties, the S242 filament is a very good example of the end-dominated collapse.

Impact of molecular mixing and scalar dissipation rate closures on turbulent bluff-body flames with increasing local extinction

Bluff-body turbulent CH4: H2 (1:1) flames at 50% (HM1), 75% (HM2) and 91% (HM3) of the blow-off velocity (235 m s−1) were studied experimentally by Masri and co-workers and found to exhibit gradually increasing periodic and shear layer instabilities. The latter are coupled with increasing levels of local extinction with subsequent re-ignition further downstream. This study provides a systematic evaluation of the sensitivity of predictions to molecular mixing and scalar dissipation rate closures. The latter include extended forms of the Euclidean Minimum Spanning Tree (EMST) and modified Curl’s (MC) models, applicable to premixed turbulent flames via a closure that accounts for local Damköhler number effects (EEMST and EMC), and a conceptually related blended scalar time-scale approach (BEMST and BMC). Computations are performed using a hybrid finite volume (FV) – transported Joint Probability Density Function (JPDF) algorithm featuring stochastic Lagrangian particles, a comprehensive 48-scalar systematically reduced C/H/N/O mechanism, and a second moment method based on the Generalised Langevin Model that provides a partial resolution of the unsteady fluid motion. The sensitivity to solution parameters affecting the temporal resolution is quantified using Fourier transforms of the time histories of velocity and scalar traces. Radial profiles, conditional means and scatter plots are compared to the experimental data along with burning indices based on the conditional mean temperature. Vortex related instabilities ∼ 1 kHz in the outer shear layer appear for all closures with EMC showing periodic local extinction and re-ignition in the neck region for HM3 and flame turbules (i.e., discrete pockets of hot gas) separating periodically at frequencies ∼ 85 Hz. Results are similar to well–resolved JPDF/LES simulations for HM1. It is shown that the EMC and (E)EMST models essentially enclose the experimental data for HM2 and HM3. For HM3, emissions of NO are controlled by local extinction events that become increasingly sensitive to the molecular mixing closure as blow-off is approached.

Power spectra prognostic aspects of impulsive eye movement traces in superior vestibular neuritis.

Since usefulness of power spectra (PS) analysis was demonstrated in many fields of electrophysiology, the aims of the present study were to evaluate differences in frequency domain values of eye velocity traces between a group of 60 healthy subjects (HC) and 35 matched superior vestibular neuritis (VN) patients and to determine prognostic aspects of such values in terms of superior VN recovery. PS calculated on video head impulse test traces was compared between HC and during the acute stage of vertigo (T1) and after 3months (T2) in superior VN patients. A multiple regression and desirability model between Δ (T2gain - T1gain) vestibulo-ocular reflex (VOR) gain and five prognostic factors were employed. Significant PS differences within the 7.8-16.6Hz domain were found between superior VN and HC. A significant negative correlation was found between the 7.8-16.6Hz domain unitary PS value and Δ VOR gain (β = - 0.836). The desirability model depicted a cutoff value of the unitary PS equal to 1.82 in order to obtain a Δ VOR gain rate at least equal to 0.1. Present findings could be a further step for monitoring those superior VN patients with systemic risk factors and high risk of VOR incomplete recovery. Graphical abstract In the top left, healthy control (HC) and superior vestibular neuritis (VN) subjects were screened by means of video head impulse test. In the top right, significant differences in power spectra values were depicted within the 7.8-16.6Hz domain when comparing the two groups of subjects. In the bottom center, the desirability model depicts a cutoff value of the power spectra equal to 1.82 in order to obtain a Δ vestibulo-ocular reflex gain rate at least equal to 0.1.

Improved adaptive integral line-of-sight guidance law and adaptive fuzzy path following control for underactuated MSV

This paper presents an adaptive fuzzy path following control law based on an improved adaptive integral line-of-sight (IAILOS) guidance law for the underactuated marine surface vessel (MSV) exposed to the time-varying ocean currents and time-varying sideslip angle. Initially, the IAILOS guidance law is proposed which can not only calculate the desired yaw angle but also estimate the time-varying ocean currents and time-varying sideslip angle simultaneously. Furthermore, the adaptive fuzzy path following control law is established by combining with the estimator to cope with the MSV’s attitude tracking control and velocity tracing control problem via backstepping technique. Specifically, the dynamic uncertainties and unknown environment disturbances are compensated by the fuzzy logic system with fuzzy updating law based on estimation error rather than tracking error. Additionally, two high-order tracking differentiators (TDs) are designed to construct derivatives of virtual control vector and reduce computational complexity inherent in backstepping method. It is proved that the proposed adaptive fuzzy path following control law can drive the vessel to track the desired path and tracking error can converge to an arbitrarily small compact set, while guaranteeing all signals in the closed-loop control system are uniformly ultimately bounded. Finally, simulation results and comparisons are carried out to demonstrate the effectiveness of the proposed control approach.

Application of Al-Cu-W-Ta graded density impactors in dynamic ramp compression experiments

Graded density impactors (GDIs) are used to dynamically compress materials to extreme conditions. Two modifications to a previously developed Mg-Cu-W GDI are made in this work before using it in a dynamic compression experiment: Mg is replaced with Al and a Ta disk is glued to the back. The Mg phase is replaced by Al because FCC Al remains solid to higher pressure along its Hugoniot compared to Mg. The addition of the Ta disk creates a constant particle velocity regime and facilitates a definition of peak pressure states. Microstructure analysis, profilometry, and ultrasonic C-scans of the Al-Cu-W GDI all confirm excellent uniformity. We evaluated signal variation in the radial direction of a dynamically compressed Al-LiF bilayer target to evaluate the contribution of spatial nonuniformity to errors. Velocity traces from five photon Doppler velocimetry (PDV) probes located at different radial distances from the center of the target varied at most by 1.1% with a root mean square of 0.3% during the compression ramp, demonstrating low PDV measurement error over a relatively large experimental area. The experimental PDV data also agrees well with 1D simulations that use inputs from predictive characterization models developed for the material properties resulting from tape casting, laminating, and powder consolidation processes. Low measurement error during quasi-isentropic compression, leading to better precision, ensures a robust platform to reach extreme compression and low-temperature recovery states and facilitates discovery via synthesis, quenching, and preservation of new high-pressure phases.

Automated analysis of fetal cardiac function using color tissue Doppler imaging in second half of normal pregnancy.

Color tissue Doppler imaging (cTDI) is a promising tool for the assessment of fetal cardiac function. However, the analysis of myocardial velocity traces is cumbersome and time-consuming, limiting its application in clinical practice. The aim of this study was to evaluate fetal cardiac function during the second half of pregnancy and to develop reference ranges using an automated method to analyze cTDI recordings from a cardiac four-chamber view. This was a cross-sectional study including 201 normal singleton pregnancies between 18 and 42 weeks of gestation. During fetal echocardiography, a four-chamber view of the heart was visualized and cTDI was performed. Regions of interest were positioned at the level of the atrioventricular plane in the left ventricular (LV), right ventricular (RV) and septal walls of the fetal heart, to obtain myocardial velocity traces that were analyzed offline using the automated algorithm. Peak myocardial velocities during atrial contraction (Am), ventricular ejection (Sm) and rapid ventricular filling, i.e. early diastole (Em), as well as the Em/Am ratio, mechanical cardiac time intervals and myocardial performance index (cMPI) were evaluated, and gestational age-specific reference ranges were constructed. At 18 weeks of gestation, the peak myocardial velocities, presented as fitted mean with 95% CI, were: LV Am, 3.39 (3.09-3.70) cm/s; LV Sm, 1.62 (1.46-1.79) cm/s; LV Em, 1.95 (1.75-2.15) cm/s; septal Am, 3.07 (2.80-3.36) cm/s; septal Sm, 1.93 (1.81-2.06) cm/s; septal Em, 2.57 (2.32-2.84) cm/s; RV Am, 4.89 (4.59-5.20) cm/s; RV Sm, 2.31 (2.16-2.46) cm/s; and RV Em, 2.94 (2.69-3.21) cm/s. At 42 weeks of gestation, the peak myocardial velocities had increased to: LV Am, 4.25 (3.87-4.65) cm/s; LV Sm, 3.53 (3.19-3.89) cm/s; LV Em, 4.55 (4.18-4.94) cm/s; septal Am, 4.49 (4.17-4.82) cm/s; septal Sm, 3.36 (3.17-3.55) cm/s; septal Em, 3.76 (3.51-4.03) cm/s; RV Am, 6.52 (6.09-6.96) cm/s; RV Sm, 4.95 (4.59-5.32) cm/s; and RV Em, 5.42 (4.99-5.88) cm/s. The mechanical cardiac time intervals generally remained more stable throughout the second half of pregnancy, although, with increased gestational age, there was an increase in duration of septal and RV atrial contraction, LV pre-ejection and septal and RV ventricular ejection, while there was a decrease in duration of septal postejection. Regression equations used for the construction of gestational age-specific reference ranges for peak myocardial velocities, Em/Am ratios, mechanical cardiac time intervals and cMPI are presented. Peak myocardial velocities increase with gestational age, while the mechanical time intervals remain more stable throughout the second half of pregnancy. Using an automated method to analyze cTDI-derived myocardial velocity traces, it was possible to construct reference ranges, which could be used in distinguishing between normal and abnormal fetal cardiac function. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Temperature Rise Effect of Permanent Magnet Wind Turbine in Different Field Settings

Temperature rise is an essential factor affecting the safety operation of electric machines. An appropriate solving domain is the first step to consider when calculating the temperature rise. However, the effect of solving domain setting on the calculation results of electric machine temperature rise has not been deeply discussed. In this paper, a 3MW permanent magnet wind generator is taken as an example. Based on the electrical and numerical heat transfer theories, two different solving domain models are established to compare the flow thermal characteristics of the internal and external ventilated paths. The fluid velocity changes in external ventilated path, the central section temperature rise and the velocity trace distribution of the internal ventilated path are compared in detail. Furthermore, the temperature rise of each component is analyzed. It is found that the fluid development in the generator is affected by solving domain selection. The results can provide a reference for accurate calculation of temperature rise of permanent magnet wind generator.

Directional Doppler in Cardiology: A 50-Year Journey

In 1968, while cardiologists were focused on cardiac structures imaged by ultrasound, Daniel Kalmanson in Paris, France, devised a new ultrasonic modality, directional continuous-wave Doppler, enabling him to record instantaneous cardiovascular blood flow velocities with recognition of their direction (relative to the transducer) in vessels. An innovative presentation of Doppler data also made velocity traces physiologically understandable. Following the noninvasive study of the arterial and venous beds, flow velocity in the right (1969) and left (1970) cardiac chambers was studied by means of a directional Doppler catheter. The curtain was then raised for the renewal of our pathophysiologic understanding of cardiac dynamics and the adoption of a new methodology. Technological evolution paved the way for clever researchers to pioneer important advances, diversifying the technique. Guided by the early principles, which are still valid in 2018, directional Doppler finally gained acceptance from the entire scientific community.

Automated analysis of fetal cardiac function using color tissue Doppler imaging.

To evaluate the feasibility of automated analysis of fetal myocardial velocity recordings obtained by color tissue Doppler imaging (cTDI). This was a prospective cross-sectional observational study of 107 singleton pregnancies ≥ 41 weeks of gestation. Myocardial velocity recordings were obtained by cTDI in a long-axis four-chamber view of the fetal heart. Regions of interest were placed in the septum and the right (RV) and left (LV) ventricular walls at the level of the atrioventricular plane. Peak myocardial velocities and mechanical cardiac time intervals were measured both manually and by an automated algorithm and agreement between the two methods was evaluated. In total, 321 myocardial velocity traces were analyzed using each method. It was possible to analyze all velocity traces obtained from the LV, RV and septal walls with the automated algorithm, and myocardial velocities and cardiac mechanical time intervals could be measured in 96% of all traces. The same results were obtained when the algorithm was run repeatedly. The myocardial velocities measured using the automated method correlated significantly with those measured manually. The agreement between methods was not consistent and some cTDI parameters had considerable bias and poor precision. Automated analysis of myocardial velocity recordings obtained by cTDI was feasible, suggesting that this technique could simplify and facilitate the use of cTDI in the evaluation of fetal cardiac function, both in research and in clinical practice. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Doppler Flow Velocity and Thermodilution to Assess Coronary Flow Reserve: A Head-to-Head Comparison With [15O]H2O PET

ObjectivesThis study sought to compare Doppler flow velocity reserve (CFRDoppl) and thermodilution-derived coronary flow reserve (CFRthermo) head-to-head with the gold standard for quantification of myocardial perfusion, [15O]H2O positron emission tomography (PET). BackgroundCoronary flow reserve (CFR) is an important parameter for assessing coronary vascular function. To date, 2 techniques are available for invasive assessment of CFR: Doppler flow velocity and thermodilution. Although these techniques have been compared with each other, neither has been compared with [15O]H2O PET perfusion imaging. MethodsCFR was assessed in 98 vessels of 40 consecutive stable patients with suspected coronary artery disease. Patients underwent [15O]H2O PET, followed by invasive angiography in conjunction with simultaneous measurements of fractional flow reserve, CFRDoppl, and CFRthermo. Both normal and obstructed arteries were included. ResultsThe quality of Doppler flow velocity traces was significantly lower than that of thermodilution curves (p < 0.001). A moderate correlation was observed between CFRDoppl and CFRthermo (r = 0.59; p < 0.001). CFRDoppl correlated well with PET-derived CFR (CFRPET) (r = 0.82; p < 0.001). In contrast, the correlation between CFRthermo and CFRPET was only modest (r = 0.55; p < 0.001). This difference in correlation with CFRPET was significant (t = 4.9; df = 95; p < 0.001). Bland-Altman analysis revealed a tendency of CFRthermo to overestimate flow reserve at higher values. ConclusionsCoronary flow reserve, determined using Doppler flow velocity, has superior agreement with [15O]H2O PET in comparison with CFRthermo.

Coupled CFD-DEM model for the direct numerical simulation of sediment bed erosion by viscous shear flow

Debris flows devastate downstream regions with large impulsive forces resulting from the significant increase in volume due to the erosion during their rapid movement. As this increase in volume is primarily derived from the sediment bed, sediment bed erosion characteristics determine the sediment transport rate and the corresponding severity degree. This study presents a coupled model based on computational fluid dynamics (CFD) and discrete element method (DEM) to simulate sediment bed erosion by viscous shear flow at various shear flow velocities. DEM is adopted to simulate the granular bed particles, and CFD is employed to model the shear flow (water and mudflows). The numerical model was verified by comparing the erosion formula and critical erosion shear stress with a pre-existing laboratory experiment. The erosion characteristics of the sediment bed were investigated from macro and micro perspectives. A sediment bed can be divided into four layers from top to bottom: saltating layer, rolling layer, creeping layer, and static layer. The depth profile of the average particle velocity obeyed a linear distribution in the rolling layer, and the velocity was approximately zero in the bottom layer. Dynamic information on the particle loss, trajectory, velocity, and principal stresses was recorded. Velocity traces demonstrated significant fluctuations with several isolated peaks, and the velocity variable displayed Gaussian distributions in the streamwise and vertical direction. The influence of the shear velocity on the drag force and sediment erosion was more obvious than those of the viscosity coefficient and fluid density. The drag force had an effect on the principal stresses and the micromechanical arrangement of the sediment grains. The results provide the insights into micro-mechanisms of the onset and erosion of sediment grains.

Diagnosis of Heart Failure With Preserved Ejection Fraction: Machine Learning of Spatiotemporal Variations in Left Ventricular Deformation

Stress testing helps diagnose heart failure with preserved ejection fraction (HFpEF), but there are no established criteria for quantifying left ventricular (LV) functional reserve. The aim of this study was to investigate whether comprehensive analysis of the timing and amplitude of LV long-axis myocardial motion and deformation throughout the cardiac cycle during rest and stress can provide more informative criteria than standard measurements. Velocity, strain, and strain rate traces were measured from all 18 LV segments by echocardiographic myocardial velocity imaging at rest and during semisupine bicycle exercise in 100 subjects aged 69±7years, including patients with HFpEF and healthy, hypertensive, and breathless control subjects. A machine-learning algorithm, composed of an unsupervised statistical method and a supervised classifier, was used to model spatiotemporal patterns of the traces and compare the predicted labels with the clinical diagnoses. The learned strain rate parameters gave the highest accuracy for allocating subjects into the four groups (overall, 57%; for patients with HFpEF, 81%), and into two classes (asymptomatic vs symptomatic; area under the curve, 0.89; accuracy, 85%; sensitivity, 86%; specificity, 82%). Machine learning of strain rate, compared with standard measurements, gave the greatest improvement in accuracy for the two-class task (+23%, P<.0001), compared with+11% (P<.0001) using velocity and+4% (P<.05) using strain. Strain rate was also best at predicting 6-min walk distance as an independent reference criterion. Machine learning of spatiotemporal variations of LV strain rate during rest and exercise could be used to identify patients with HFpEF and to provide an objective basis for diagnostic classification.

Temperature and velocity fields of the gas-vapor flow near evaporating water droplets

Experimental studies of unsteady temperature and velocity fields of the gas-vapor flow in the immediate vicinity of evaporating water droplets were performed in the interests of developing high-temperature (over 300°С) gas-vapor-droplet applications. The formation time of virtually homogeneous (temperature variations of under 2–3°С) temperature fields of evaporating water droplets was established using Particle Image Velocimetry, Laser Induced Phosphorescence, Planar Laser Induced Fluorescence. We observed highly inhomogeneous and unsteady temperature and velocity fields of the gas-vapor mixture and determined the lateral and transversal dimensions of the aerodynamic and thermal traces of evaporating water droplets. The degree of impact of several parameters on the latter was evaluated: initial temperature (20–500 °C) and velocity of the incoming flow (0.5–5 m/s), as well as the initial droplet size (1–2 mm). The role of evaporation and convective heat exchange between a droplet and gases in forming of thermal and aerodynamic trace was analyzed. The heat flow density was found to vary nonlinearly with time (in the immediate vicinity of an evaporating droplet), and the impact of droplet trace temperature and velocity on the heat flow density was evaluated. Both advantages and limitations of the used techniques are established in terms of reliable plotting of unsteady temperature and velocity fields of gas-vapor mixture in the trace of evaporating water droplets, considering the heating lag of the latter.