Doppler effect, flow measurement

Doppler Effect. Laser Doppler anemometry utilizes the Doppler effect to measure instantaneous particle velocities. When particles suspended in a flow are illuminated with a laser beam, the frequency of the light scattered (and/or refracted) from the particles is different from that of the incident beam. 

Flowmeters These are used to measure flocculant addition, underflow, and feed flow rates. For automatic control, the more commonly used devices are magnetic flowmeters and Doppler effect flowmeters. 

This aspect is not included here, but is related to optical flow diagnostics. It is based again on the principle of the optical Doppler effect. Multifunctional equipment is available for noncontact measurements of flow-induced vibration on surfaces of structural elements, for acoustic measurements, and for calibration of accelerometers and vibration transducers. 

The Doppler effect is produced by changes in wavelength due to the reflection of sound on moving particles (e. g. erythrocytes). Consequently, the direction of flow (away from or towards the sound source) as well as hsflow rate in arterial and venous vessels can be determined. The fhw volume is then calculated by additional sonographic measurement of the vessel diameter. It has been shown that the rate of flow is clearly dependent upon the respiratory activity, so that an increase in blood flow velocity can be determined with maximum exspiration as well as postprandially (normal value 18-30 cm/sec). (14, 19, 32, 34, 42, 77, 91, 162)... 

The chapter begins with the fundamental measurements of resistance, capacitance, charge, and particle force. We proceed with flow measurements with various probes followed by a listing of some commercial electrostatic instruments. Nonelectrosatic measurements in multiphase flow such as the laser-Doppler anemometer, radioactive tracers, and stroboscopic techniques (Polaskowski, et. al, 1995 Soo, 1982) have not been discussed unless in relation to an electrostatic effect. 

To study the effect of PGDN on cerebral blood flow, Godin et al. (1995) injected male Sprague-Dawley rats (through a jugular vein cannula) with PGDN at 0.1 to 30 mg/ kg and measured cerebral blood flow with a fiberoptic laser-Doppler flow probe in contact with the brain. Following a small initial drop in cerebral perfusion that lasted 1 min, blood flow rapidly increased and reached a maximum 2 min after injection. The increase in perfusion was correlated with dose, but due to the small number of animals and individual variability, a clear dose-response relationship was not obtained. 

There have been very few studies of the effects of non-Newtonian properties on flow patterns in hydrocyclones, although Dyakowski et al.,AU have carried out numerical simulations for power-law fluids, and these have been validated by experimental measurements in which velocity profiles were obtained by laser-doppler anemometry. 

The effects of raloxifene on the vascular endothelium have been studied in 19 subjects who underwent endothelial function testing at baseline and after treatment with placebo or raloxifene (60 mg/day for 6 weeks) (27). The findings in this small short-term study were entirely positive. Brachial artery diameter change (flow-mediated dilatation) increased 5.0% with placebo and 8.6% with raloxifene in response to a hyperemic stimulus. The ratio of AUC response to AUC reference with the use of laser Doppler measures was 1.18 for placebo and 1.28 for raloxifene. Flow-mediated dilatation and AUC ratio correlated significantly. The authors concluded that raloxifene enhanced endothelial-mediated dilatation in brachial arteries and digital vessels in these women, and they discussed the drug s possible cardioprotective effect. 

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