Disturbances of the performance

In spite of all these difficulties, the threshold spectrometer described has demonstrated high performance capabilities, and one special application will be presented 

The ideal performance of an electron spectrometer can be disturbed considerably by several effects which will be discussed below. These include influences from 

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One measure of the performance of a control system is the variance of the controlled variable from the target. Both improving the control svstem and reducing the disturbances will lead to a lower variance in the controlled variable. 

The demands and design of a local ventilation system (not only local ex hausts) should naturally start with the demanded target levels and the toxicity of the air contaminants (see Chapters 5 and 6). For best performance the exhaust should be close to the source and preferably enclose the source, there should be no disturbances of the flow, and at the same time it should have a low flow rate and be able to minimize the concentration of even quite dangerous air contaminants in the working zone. 

Converting the small currents measured at ultramicro electrodes results in higher current densities compared with the values obtained at micro electrodes. This is also caused by the spherical diffusion path. This effect improves on the sensitivity and the detection limit for analytical purposes, and the small size of the electrodes in combination with application of high scan rates allow measurement to be performed in vivo and with a minimal (negligible) disturbance of the conditions of the system to be analysed. 

This is, when properly performed, the most accurate method available for determining surface tensions. Since the measurements do not involve a disturbance of the surface, slow time effects can be followed. 

This requires numerical integration. As pointed out at the outset, these estimates of the mass transfer performance are likely to be conservative as the disturbance of the film by ripples has been neglected. This will reduce the exposure time significantly, particularly with inviscid liquids. 

Figure 4.15 Relative transmission T (called here the collecting efficiency ) of a CMA as a function of the kinetic energy of the electrons. The solid curve guides the eye through the experimental data. For energies higher than 4eV the transmission is constant, below this value it drops to zero (the cut-off effect due to disturbances in the performance of the analyser caused by residual magnetic fields and inhomogeneities of electrical fields, see Sections 4.5.2 and 4.5.3). Reprinted from J. Electron Spectrosc. Relat. Phenom., 15, Samson, 257 (1979) with kind permission of Elsevier Science - NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands.

Table 2.43 lists the equations to be used in determining the proportional, integral, and derivative settings for a PID controller tuned for load disturbance using the various criteria listed in Table 2.44. The selection of the performance criteria can be done manually or automatically (per programming).

Hyperinflation of the lung by vigorous exercise or repeatedly performing lung function tests may also lead to increased membrane permeability, possibly resulting from a disturbance of the intercellular junctions. 

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