Strobe effects

Strobe effects are characterized by repeated flashes of light produced by a single pyrotechnic unit (for example, a star). 

Lighting from a 50 or 60 Hz alternating current electrical source can result in strobe effects on moving parts, making them appear to move slowly, move backwards or appear stationary. Machinists on lathes, for example, should be made aware of this. 

Beckman Elutriation Method. The Beckman elutriation method uses a chamber designed so that the centrifugal effect of the radial inward fluid flow is constant (Fig. 3). The separation chambers are made of transparent epoxy resin which faciUtates observation of the movements of the cell boundary in strobe light illumination. This enables detection of the radius at which the cells are separating. When a mixture of cells, eg, mononuclear white cells, enters the chamber, separation can be achieved by fine tuning centrifuge speed and inward fluid flow to the specific cell group. This is a laboratory method suitable for relatively small numbers of cells. Chambers are available in sizes to handle 2-3 x 10 , 1 2 x 10 , and 1 x 10 ° cells. The Beckman chambers can be appHed to collect mononuclear cells from bone marrow aspirates. 

The flow regimes in the test sections were identified visually with the aid of a strobe and a digital camera. The camera was always targeted at the test section center. No systematic attempt was made to assess and eliminate the test section entrance effects on the flow regimes. However, the distance between the point pictured by the camera and the test section inlet was well over 100 channel diameters everywhere. Thus, although the possibility exists that the reported flow regimes are influenced by the test section entrance conditions, this influence may not be significant. 

Under regular light, it is difficult to see the waves traveling back and forth. For a better view, pluck the rubber band in front of a computer monitor or a television screen that uses a cathode ray tube. The light from these devices, which acts like a strobe light, makes the waves appear to slow down Vary the tension in the rubber band to see different effects. 

The name strobe technique comes about because the photomultiplier PMT is gated -or strobed - by a voltage pulse that is synchronized with the pulsed light source. The strobe has the effect of turning on the PMT and measuring the emission intensity over a very short time window (Figure 7.6) (Bennett 1960 James et al. 1992). 

Figure 3. Relative integrated signal showing the effect of lag as a function of dwell time controlled by channel time. Each channel consisted of500 pixels (delta Y = 500). Signal is due to a single pulse of a Xe strobe lamp (General Radio, 1539-A Stroboslave). Light was detected in zero order with a 20-p.m entrance slit. Dwell time o, 40 ns , 80 ns A, 160 ns ...

When these wavelengths superimpose in phase they are said to be mode-locked and behave as a wave packet or pulse. The pump and probe pulses are focused into a chamber containing gaseous molecules for study. The pump pulse excites a change (e.g., chemical reaction) while absorption of the probe pulse monitors the course of structural change as time passes on the fs scale. Zewail has likened the process to the effects of a strobe light that furnishes stop-action pictures of a fast process. 

Herr, D.W. and Boyes, W.K., 1993. Potential confounding effects of strobe clicks in flash evoked potentials (FEPs) in rats. Toxicologist 13 fabstractV. 216. 

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