The manufacture of polymer components for biomedical applications is an area which has received much attention from polymer scientists, with high levels of wear resistance achieved, but relatively little research has been done into the machining operations required to manufacture the complex geometries used in total joint replacement. Traditional metal cutting theories have been shown to be insufficient for analysis of polymer machining, as polymers exhibit viscoelastic behaviour, and unique chip formation mechanisms. This paper details an experimental investigation into the effect of tooling and machining parameters on the cutting forces, surface roughness and chip formation in Ultra High Molecular Weight Polyethylene, a common material used in biomedical applications. This research quantifies the relative importance of each parameter, the chip formation mechanisms and resulting surface roughness for the given machining parameters, and provides new insight into applied research on the machining of polymers.
The authors diagnosed depression in 20 (23%) of 88 cognitively impaired geriatric outpatients. Three (20%) of these patients had depression only, and 17 (85%) had depression superimposed on an underlying dementia. The rate of coexisting depression decreased significantly with greater severity of the cognitive impairment: 9 (33%) of 27 mildly impaired patients were depressed, compared with 8 (23%) of 35 moderately impaired and 3 (12%) of 26 severely impaired patients. There was a nonsignificant trend for cognitively impaired women to be more likely to be depressed than for similarly impaired men. The authors conclude that although depression must be differentiated from dementia, it is equally important to consider the possibility that the diagnoses coexist.
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