ABSTRACT
This article describes a prototype continuous flow ventricular assist device (CFVAD3) supported in magnetic bearings. The VAD is a small centrifugal four bladed pump. The pump's geometry is explained. The CFVAD3 is the first compact VAD completely supported in magnetic bearings. The magnetic bearings are composed of an inlet side actuator divided into eight pole sets, and an outlet side actuator, also divided into eight pole sets. The pump operating performance was tested and found to be within the design flow rate of up to 9 L/min, and head up to 170 mm Hg for human circulatory support. Magnetic bearing operation out of center positions under various operating orientations were measured and found to be < 1/6 of the bearing clearance, well within specifications. The expected magnetic bearing power loss has been calculated at approximately 6.5 watts.
Subject(s)
Heart-Assist Devices , Magnetics , HumansABSTRACT
Hydrodynamic forces occur on lenses due to pressures created in tear films during squeeze motions. Pressures and squeeze forces are calculated for lenses with both flat and steepened base curve radii. A parabolic two-dimensional tear film tickness is assumed for calculation purposes. A tear film with a peripheral film thickness of one-half of the central film thickness produces over three times the squeeze force produced by a constant tear film thickness with the same central clearance. Also, the distance moved by the lens toward the corneal surface is determined.
Subject(s)
Contact Lenses/standards , Humans , Mathematics , Physical Phenomena , Physics , Pressure , Stress, Mechanical , TearsABSTRACT
The strain in thin flexible membranes representing human skin has been studied using moiré interferometry. A method of using a flexible coating of photographic emulsion was developed. The equations for use in differential interferometry were also derived for very large deformations. The method was applied to two types of cases: rectangular membranes subjected to a uniform axial strain, and membranes containing strain concentrators that represent bandages placed on the surface of the skin. Results for the former case were within 3% of exact results, while results near the concentrator indicate strain concentration factors ranging from -1.25 to 1.75.
