This article reviews the physiology of penile erection, the components of erectile function, and the pathophysiology of erectile dysfunction. The molecular and clinical under-standing of erectile function continues to gain ground at a particularly fast rate. Advances in gene discovery have aided greatly in working knowledge of smooth muscle relaxation/contraction pathways. The understanding of the nitric oxide pathway has aided not only in the molecular understanding of the tumescence but also greatly in the therapy of erectile dysfunction.
Two simple analyses are developed to predict losses in centrifugal compressor (or pump) vaneless diffusers: (a) One-dimensional, axisymmetric friction loss and (b) sudden-expansion mixing to account for losses in the diffuser caused by wakes of separated impeller blades. It is shown that these theories may be substituted for the more complex theory of Dean and Senoo [5]. Some experimental data are included to show the validity of the friction-loss analysis. Finally, the utility of the analyses in design is demonstrated.
Experimental investigations have shown that the flow discharged from a centrifugal compressor or pump impeller into a diffuser is often unsteady and axially asymmetric. A theory based upon a simplified model is developed for this type of flow. The theory predicts a significant reversible work transfer between parts of the flow with different velocities. This effect only occurs in cases of rotating distortion patterns; stationary distortion patterns, therefore, behave differently. Theoretical results are compared to measurements and good agreement is found. The implications of the theory have been investigated by means of machine computations and are discussed herein.
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