This study predicts that saccadic eye movements and normal head movements after vitrectomy and gas tamponade generate only small fluid shear stresses on the retina that are below published norms for retinal adhesion strength. Sudden, jerking head movements generate fluid shear forces similar to retinal adhesion strength that localize to the area of gas-fluid interface. Fluid sloshing occurs after movement, but rapidly decays on cessation of movement. These results suggest that restrictive posturing after vitrectomy and gas tamponade may be unnecessary. Patients should avoid sudden head movements.
A 3-D configuration of a T-mixer is evaluated under normal operating conditions of the called convective micromixers. The design has been called 3-D T-mixer in our previous work [1] as it adopts a three-dimensional structure at the T-junction. This design feature has been found that it exerts a strong effect on the flow characteristics in the device downstream in the mixing channel. A numerical study has been carried out in the 3-D T-mixer and the typical T-mixer, being these modelled with equal dimensions of channel lengths and cross sections and operated with the same flow rates. The flow analysis in the 3-D T-mixer reveals the quick formation of vortical flow structures composed of intertwined fluid filaments which increase drastically the fluids interface to enhance mixing. The flow patterns in the mixing channel vary with Reynolds number (Re) in the range 100-500. This study shows that the 3-D T-mixer provides a significant enhancement of mixing and presents lower pressure loss and similar level of shear stress compared to a typical T-mixer, in the whole range of Re used to characterize the flow. It has a simple channel configuration which is easy to fabricate and effective for mixing of continuous fluid and potentially particles. The 3-D T-mixer is called to be tested and applied for improving the efficiency of systems which have a T-junction in their design and require fast mixing with high throughput
Purpose. To establish a theoretical model to determine the relationship between retinal coverage and tamponade shape in relation to tamponade volume, for a variety of tamponades, and to test these relationships with a physical analogue of the human eye. Methods. The theoretical model was based on a static balance between buoyancy forces and surface tension forces, for an axisymmetrically shaped bubble or droplet. In the laboratory experiments, two hemispheres were cut into an acrylic block. The acrylic was soaked with bovine serum for 10 minutes to ensure that the wetting properties were similar to the human retina. Photographic images of various fractions of lighter-than-water (gas, silicone) and heavier-than-water (Oxane HD) tamponades were analyzed by using algorithms written in commercial image-processing software and compared with the theoretical predictions and published data. Results. The theoretical predictions of tamponade shape and retinal coverage agree closely with the results obtained from the analogue experiments. Conclusions. The theoretical model was validated against measurements in a human eye analogue and published data. The three key parameters that characterize the retinal coverage of any given tamponade are the bond number, the contact angle of the tamponade, and the volume used. The model may be used to predict the static properties of new tamponades without in vivo tests.
The characteristics of a double-chamber valveless parallel micropump are analysed using a one-dimensional non-linear model. The relationships between the mean volume flux, pressure difference and (measurable) characteristics of the pump are derived in a closed-form expression which are validated against the numerical solutions. These results show that when pump chambers are driven exactly out of phase, the volume flux is maximum and the variation of the pump chamber pressure is (significantly) reduced. The model predictions were tested against the experimental results of Olsson et al. (Sens Actuators A Phys 47:549-556, 1995) for both in and out of phase pumps. The mean volume flux decreases linearly with pressure rise. For both cases, the agreement is good and is an improvement over previous analytical models. The implications of these results for optimal pump design are discussed
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