The flow through a curved tube whose radius of curvature varies with time was studied in order to better understand flow patterns in coronary arteries. A computational flow model was constructed using commercially available software. The artery model featured a uniform circular cross section, and the curvature was assumed to be constant along the tube, and in one plane. The computational model was verified with the use of a dynamically similar in vitro apparatus. A steady uniform velocity was prescribed at the entrance at a Reynolds number of 300. Two sets of results were obtained: one in which the curvature was held constant at the mean, maximum and minimum radii of curvature (quasistatic), and another in which the curvature was varied sinusoidally in time at a frequency of I Hz (dynamic). The results of the dynamic analysis showed that the wall shear rates varied as much as 52% of the static mean wall shear rate within a region of 10 tube diameters from the inlet. The results of the dynamic analysis were within 6% of the quasistatic predictions. Realistic modeling of the deforming geometry is important in determining which locations in the coronary arteries are subjected to low and oscillating wall shear stresses, flow patterns that have been associated with atherogenesis.
Atherosclerosis of the human arterial system produces major clinical symptoms when the plaque advances to create a high-grade stenosis. The hemodynamic shear rates produced in high-grade stenoses are important in the understanding of atheromatous plaque rupture and thrombosis. This study was designed to quantify the physiologic stress levels experienced by endothelial cells and platelets in the region of vascular stenoses. The steady hemodynamic flow field was solved for stenoses with percent area reductions of 50, 75, and 90 percent over a range of physiologic Reynolds numbers (100-400). The maximum wall shear rate in the throat region can be shown to vary by the square root of the Reynolds number. The shear rate results can be generalized to apply to a range of stenosis lengths and flow rates. Using dimensions typical for a human carotid or coronary artery, wall shear rates were found to vary from a maximum of 20,000 s-1 upstream of the throat to a minimum of -630 s-1 in the recirculation zone for a 90 percent stenosis. An example is given which illustrates how these values can be used to understand the relationship between hemodynamic shear and platelet deposition.
PurposeThe purpose of this paper is to focus on the question of what accounts for appropriate performance reports in the context of the new public management (NPM), and how they can deliver the information they need to politicians.Design/methodology/approachThe study is based on a survey of members of cantonal and federal members of governments and parliaments, where performance contracting has been introduced; 454 questionnaires answered.FindingsThe results of the study reflect the distinct roles of the parliament in the performance contracting process. On the content side of the reports, they are expected to contain general as well as detailed information. Outcome rather than output indicators are demanded, especially by parliamentarians. There is, also, a need for “early warning indicators” of long‐term threats, and extra‐ordinary incidents. Formally, a homogeneous reporting format across government should be realized. Reports are expected to be well visualized and to contain the most relevant indicators. Changes and deviations should be commented on. Reports should be printed, additional electronic publication would be accepted; external revision is considered to be necessary. Regarding time‐related aspects, the assumption is confirmed that political decision makers have very little time to deal with the reports. Reporting has to be as up to date as possible. Parliaments demand a one‐ or two‐year rhythm; governments require annual or even semi‐annual reports.Originality/valueUp to now, public management research has addressed the issue of appropriate performance reporting insufficiently, despite the fact that the central concept of outcomes is a political concept. The research question answered in this paper – what the essential components of appropriate performance reports under NPM conditions, and how should they be characterized in order to give politicians the performance information they need, provides some public management research in a Swiss context.
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