Characterization of Left Ventricle Main Flow Axis Line Using Echodynamography

<span>Left ventricular (LV) blood flow analysis may play an essential role in evaluating cardiac function besides the classical analysis of wall motion. Echodynamography is an imaging method in which two-dimensional (2D) blood flow vectors are deduced by blood flow information obtained by color Doppler echocardiography. Echodynamography has provided useful information on the blood flow pattern in healthy and abnormal LV. The main flow axis line (MFAL) is defined as a maximum velocity magnitude of blood flow from the LV's apex to LV's outflow, which is a new hemodynamic parameter for cardiac assessment. The present study's objective is to compare blood flow patterns between healthy and abnormal LV by investigating the MFAL and its correlation to vorticity and velocity distribution on MFAL. This study enrolled 12 participants, four healthy volunteers, and eight abnormal patients. Echodynamography analyzed frame by frame Doppler image of apical three-chamber views. The results showed MFAL superimposed on vorticity mapping during ventricular ejection and MFAL path coincide with the irrotational flow of zero vorticity path, ω = 0. A significant difference was observed in the velocity distribution curve (VDC) on the MFAL during early, mid, and late systoles compared to healthy and abnormal LV. VDC showed the linear upward curve and the highest velocity magnitude during the early systole phase in healthy LV. In contrast with abnormal LV, VDC showed the downward convex curve and the highest velocity magnitude during mid systole phase. Furthermore, the gradient and slope angle of the VDC on the MFAL was compared. The result showed that the maximum gradient and slope angle were not significantly different between healthy and abnormal LV. In conclusion, the study of MFAL and the correlation to vorticity based on the Echodynamography computational program provides additional insights for representing a cardiac function, and thus, the clinical implications of MFAL warrant further investigation.</span>

Gas evolution in electrochemical flow cell reactors induces resistance gradients with consequences for the positioning of the reference electrode

The gas evolution during electrolysis in flow cells results in inhomogeneous distributions of resistance, current and voltage along the flow axis.

HH 175: A Giant HH Flow Emanating From A Multiple Protostar

HH 175 is an isolated Herbig-Haro object seen towards the B35 cloud in the λ Ori region. We use deep Subaru 8m interference filter images and Spitzer images to show that HH 175 is a terminal shock in a large collimated outflow from the nearby embedded source IRAS 05417+0907. The body of the eastern outflow lobe is hidden by a dense ridge of gas. The western outflow breaks out of the front of the cometary-shaped B35 cloud, carrying cloud fragments along, which are optically visible due to photoionization by the massive λ Ori stars. The total extent of the bipolar outflow is 13.7 arcmin, which at the adopted distance of 415 pc corresponds to a projected dimension of 1.65 pc. The embedded source IRAS 05417+0907 is located on the flow axis approximately midway between the two lobes, and near-infrared images show it to be a multiple system of 6 sources, with a total luminosity of 31 L⊙. Millimeter maps in CO, 13CO, and C18O show that the B35 cloud is highly structured with multiple cores, of which the one that spawned IRAS 05417+0907 is located at the apex of B35. It is likely that the embedded source is the result of compression by an ionization-shock front driven by the λ Ori OB stars.

Inertial effects on the dynamics, streamline topology and interfacial stresses due to a drop in shear

Deformation of a viscous drop in shear at finite inertia and the streamlines around it are numerically investigated. Inertia destroys the closed streamlines found in Stokes flow. It creates reversed streamlines and streamlines spiralling around the vorticity axis. Spiralling streamlines spiral either towards the central shear plane or away from it depending on the viscosity ratio and the inertia. The zones of open or reversed streamlines as well as streamlines spiralling towards or away from the central shear plane are delineated for varying viscosity ratio and Reynolds number. In contrast to the infinite extent of the closed Stokes streamlines around a rigid sphere in shear, the region of the spiralling streamlines in the vorticity direction both for a rigid sphere and a drop shrinks with inertia. Inertia increases deformation, and introduces oscillations in drop shape. An approximate analysis explains the scaling of oscillation frequency and damping with Reynolds and capillary numbers. The steady-state drop inclination angle with the flow axis increases with increasing Reynolds number for small Reynolds number. But it decreases at higher Reynolds number, especially for larger capillary numbers. For smaller capillary numbers, drop inclination reaches higher than $4{5}^{\ensuremath{\circ} } $ (the direction of maximum extension), critically affecting the interfacial stresses due to the drop. It changes the sign of first and second normal interfacial stress differences (and thereby these components of the effective stresses of an emulsion of such drops). Increasing viscosity ratio orients the drop towards the flow axis, which increases the critical Reynolds number above which the drop inclination reaches more than $4{5}^{\ensuremath{\circ} } $.

Experimental Investigation of Helical Cross-Flow Axis Hydrokinetic Turbines, Including Effects of Waves and Turbulence

The performance characteristics of two cross-flow axis hydrokinetic turbines were evaluated in UNH’s tow and wave tank. A 1m diameter, 1.25m (nominal) height three-bladed Gorlov Helical Turbine (GHT) and a 1m diameter, four-bladed spherical-helical turbine (LST), both manufactured by Lucid Energy Technologies, LLP were tested at tow speeds up to 1.5 m/s. Relationships between tip speed ratio, solidity, power coefficient (Cp), kinetic exergy efficiency, and overall streamwise drag coefficient (Cd) are explored. As expected, the spherical-helical turbine is less effective at converting available kinetic energy in a relatively low blockage, free-surface flow. The GHT was then towed in waves to investigate the effects of a periodically unsteady inflow, and an increase in performance was observed along with an increase in minimum tip speed ratio at which power can be extracted. Regarding effects of turbulence, it was previously documented that an increase in free-stream homogenous isotropic turbulence increased static stall angles for airfoils. This phenomenon was first qualitatively investigated on a smaller scale with a NACA0012 hydrofoil in a UNH water tunnel, using an upstream grid turbulence generator and using high frame-rate PIV to measure the flow field. Since the angle of attack for a cross-flow axis turbine blade oscillates with higher amplitude as tip speed ratio decreases, any delay of stall should allow power extraction at lower tip speed ratios. This hypothesis was tested experimentally on a larger scale in the tow tank by creating grid turbulence upstream of the turbine. It is shown that the range of operable tip speed ratios is slightly expanded, with a possible improvement of power coefficient at lower tip speed ratios. Drag coefficients at higher tip speed ratios seem to increase more rapidly than in the non-turbulent case.

Analytical and Numerical Modeling of Performance Characteristics of Cross-Flow Axis Hydrokinetic Turbines

A model for cross-flow axis hydrokinetic turbines based on blade element theory (BET) was developed. The model combines an extensive experimental and numerical high Reynolds number data set for symmetric airfoils with governing equations to predict performance characteristics of the turbines. The model allows for any number of turbine blades and for variable hydrofoil sweep angles; both straight blade (H-Darrieus) and helical blade (Gorlov) cross-flow axis turbines are modeled. In this model the free stream velocity and the turbine’s rate of rotation are not coupled hydrodynamically, and experimental calibration of the model for a specific turbine design is necessary. The calibrated model is then used with real inflow data from an actual tidal energy site to predict instantaneous power and energy yield over a period of time. Investigation of tip speed ratios allows for predictions of unsteady loadings, optimal performance and power outputs. The model provides the versatility to predict characteristics of many different shapes and sizes of cross-flow axis turbines. Through investigation of turbine stall characteristics predicted by the model, two, turbine-specific tip speed ratios of interest were determined: the critical and optimal tip speed ratios. The “critical tip speed ratio” is defined as the tip speed ratio above which there are no longer regions of negative torque during the turbine rotation. The “optimal tip speed ratio” is defined as the tip speed ratio for which the coefficient of torque, averaged over one rotation, is maximized. It is hypothesized that these tip speed ratios correspond to specific turbine operating points: A turbine operating under no load conditions will spin near the optimal tip speed ratio, and a turbine operating at peak power conditions will spin near the critical tip speed ratio.