Layer Excitation

The usual procedure in dc arc excitation is to make the lower electrode, containing the sample, the anode and the counter (upper) electrode the cathode. This method facilitates the volatilization of the sample into the arc gap. 

however, the lower sample holding electrode is made the cathode, metal vapors emerging from the sample are retained by the electrical field in a region just above the cathode for a longer period of time. The result is a region of high metal vapor concentration just above the cathode known as the cathode layer. Spectroscopically, the result of the formation of the cathode layer is enhanced spectral line intensity in the cathode layer region. 

The cathode layer technique is especially useful for small samples since the electrical forces retaining the metal vapor in this region can have their maximum effect. Some increase in background also is noticed in the cathode layer so line-to-background measurements may not be noticeably improved when using this technique. 

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Flow separation in boundary layer exciting blades... 

However, the method will not enhance the external quantum yield of the LED, moreover, proper optical coupling between the layers has to be achieved in order not to decrease the QY loo much [61. One of the obvious problems is the principal requirement of having the ITO-covered glass substrate between the color converter and the cmitLer layer. This can also lead to color bleeding, an effect where the emitter layer excites not only the conversion layer, it is supposed to address but also neighboring ones. 

Preliminary activation may be performed not only by means of dissociation of the components being analyzed, but also by electronic and vibrational excitation, either in the gaseous phase, or even better, directly on the film of semiconductor sensor. It should be also noted that this method is applicable to dissociation in the adsorbed layer. Excitation of the molecules in adsorbed layer (we are referring to physically adsorbed particles) can be performed optically, by an electron (ion) beam, or by an electronically excited atom beam, by Hg, for example [10, 11]. 

McManus, K.R., V. Vandsburga, and C.T. Bowman. 1990. Combustor performance enhancement through direct shear layer excitation. Combustion Flame 82 75-92. 

One of the reasons that the transition process is somewhat intractable is due to the fact that the receptivity process is inadequately understood for cases other than the wall excitation case, as discussed above. This intractability is specifically the case for shear layers excited by sources outside the viscous layer in the free stream, for many reasons. Firstly, unlike the wall excitation case where the applied disturbance is uniquely located at the wall, for free stream excitation the response would be different depending upon the height of the exciter in the free stream - a parameter that can... 

The two-dimensional Navier-Stokes equation is solved in stream function-vorticity formulation, as reported variously in Sengupta et al. (2001, 2003), Sengupta Dipankar (2005). Brinckman Walker (2001) also simulated the burst sequence of turbulent boundary layer excited by streamwise vortices (in X- direction) using the same formulation for which a stream function was defined in the y — z) -plane only. To resolve various small scale events inside the shear layer, the vorticity transport equation (VTE) and the stream function equation (SFE) are solved in the transformed — rj) —... 

Leehey, P. and Shapiro, P. (1979). Leading edge effect in laminar boundary layer excitation by sound. In Laminar Turbulent Transition (eds. R. Eppler and H. Fasel), 321-331, Springer Verlag. 

Sengupta, T.K., Nair, M.T. and Rana, V. (1997). Boundary layer excited by low frequency disturbances- Klebanoff mode. J. Fluids Struct., 11, 845-853. 

The Stokes-layer excitation in a cylindrical duct is one of the effective techniques for dynamic calibration of shear stress sensors [8]. The flow inside the duct is driven by an oscillating pressure gradient generated by a loud speaker (see Fig. 10). The loud speaker driven by an amplifier generates an acoustic wave. The amplifier receives sinusoidal input from a function generator. The microphone and shear stress sensor are mounted at opposite locations of the tube. The data acquisition system records the signal from the microphone and shear stress sensor. 

Sheplak M, Padmanabhan A, Schmidt MA, Brener KS (2001) Dynamic calibration of a shear-stress stat-sor using Stokes-layer excitation. AIAA... 

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