Variation sensitivity

The encircling probe was characterised with its mirror in water. As we did not own very tiny hydrophone, we used a reflector with hemispherical tip with a radius of curvature of 2 mm (see figure 3c). As a result, it was possible to monitor the beam at the tube entrance and to measure the position of the beam at the desired angle relatively to the angular 0° position. A few acoustic apertures were verified. They were selected on an homogeneous criteria a good one with less than 2 dB of relative sensitivity variations, medium one would be 4 dB and a bad one with more than 6 dB. 

The advantages of SIMS are its high sensitivity (detection limit of ppms for certain elements), its ability to detect hydrogen and the emission of molecular fragments that often bear tractable relationships with the parent structure on the surface. Disadvantages are that secondary ion formation is a poorly understood phenomenon and that quantification is often difficult. A major drawback is the matrix effect secondary ion yields of one element can vary tremendously with chemical environment. This matrix effect and the elemental sensitivity variation of five orders of magmtude across the periodic table make quantitative interpretation of SIMS spectra oftechmcal catalysts extremely difficult. 

The product distribution in this reaction was found to be dependent upon the triplet energy of the sensitizer. Variation of the relative amounts of cyclobutanes (32) and (33) to cyclohexene (34) with sensitizer triplet energy... 

The cell diagrammed in Figure 29.20c has been used extensively by Kastening to study the reaction mechanisms and kinetics when a stable electro-chemically generated species is mixed with other reactants [38]. The calculations that were used to reduce the experimental data to kinetic parameters included the effects of flow rate, reaction mechanism, rate constant, and the dependence of the EPR spectrometer nonuniform sensitivity to the position of the radicals in the cavity. Unfortunately, the correction for the latter effect was introduced as the idealized cosine-squared function (solid line in Fig. 29.16) rather than the actual sensitivity variation that occurs with magnetic field modulation. It is important to be aware of this difficulty when performing experiments to determine accurate kinetic parameters. 

These two techniques may be applied in a gentle manner using a near static ion beam to produce little change in the surface and also in a mode in which chemical profiling with depth is possible. ISS can detect all of the elements heavier than helium in the periodic table. The sensitivity variation across the periodic table is probably less than one order of magnitude. 

Checks for possible sensitivity changes (due to window transmission) were made during the course of the data acquisition. The maximum sensitivity variation observed over a one hour period of lean engine operation was 2.4 percent change in the mean value. 

As discussed earlier, the PEM is, in many ways, an ideal modulation device for polarization-selective measurements. Thus, the optimum simultaneous multiwavelength CD instrument should incorporate both the PEM and CCD, and at the same time allow the PEM to operate at its resonant frequency. One way to overcome the basic incompatibility of the PEM and CCD is to use an optical demodulation scheme in which the two oppositely polarized components would be directed by a polarizing beamsplitter, to either different areas of the same CCD, or to different CCDs [14]. Since two distinct detector areas would be accessed by the oppositely polarized light, pixel-to-pixel sensitivity variations may be a significant source of noise. 

Elemental sensitivity Elements Z > 2 Specificity very good Sensitivity variations 50 x... 

TABLE 4.6 Effect of Sensitizer Variation on Reaction Periselecitivity Between 8a and 13a in CH2CI2... 

Henderson-Sellers a.. Climate sensitivity variations in vegetated land surface albedos. In Proc. 6th Annual Climate Diagnostic Workshop, Columbia University , 155, 144 (October 14-16, 1981). 

Note that equation (12.88) has exactly the same structure as equation (12.10). Therefore, we can apply any of the differential methods, introduced in this chapter, to find the magnetic and electric field sensitivities (variations and E). 

Although at this time the sensitivity variations seen when changing injection volume with saline samples cannot be explained, it is clear that... 

The above technique requires organic layers that are of the order of a few microns thick, considerably thicker than those used in OFEDs. A way to measure charge carrier mobilities directly on an OFED geometry is by time-resolved electroluminescence measurements. The technique is based on the fact that for recombination to take place, the most mobile of the two carriers needs to transverse the sample and meet with the less mobile one [120, 121]. Therefore, the time onset for emission corresponds to the transit time of the most mobile carrier. Blom et al. [122] have described a high sensitivity variation of this technique where the time integrated light output is measured as a fimction of the duration of a voltage pulse and the transit time is extracted by extrapolation to... 

Inductively coupled plasma-mass spectrometry (ICP-MS) is a modern and more sensitive variation of MS detection of bismuth. Bismuthine is generated in a hydride generator and swept by argon directly into the ICP unit. The ions are then introduced into the mass spectrometer. Optimization of the mass spectrometer, reagent, and gas flow parameters leads to a detection limit of 20ngL (IfQand 1993). Phillips etal. (2001) examined the safety aspects of colloidal bismuth subcitrate (CBS) quadruple therapy for Helicobacter pylori. These authors used ICP-MS to determine blood Bi levels in 34 patients receiving CBS quadruple therapy, with whole blood Bi levels being deter-... 

The above specifications lead normally to rapid convergence. Alternative specifications may be used, but some are not always feasible. For example, specifying the recovery of a key component and product rate gives convergence if the column design is appropriate. The specification of product purity is difficult, sometimes impossible, because now recovery and distillate rate are interdependent. Similarly, the specification of a tray temperature is linked by composition and vapour/liquid flows. Generally, these specifications are indirect and may be seen as of control type. They require the manipulation of other variables. A controlled specification is feasible if the unit design is appropriate and if it shows continuous and sensitive variation with the manipulated variable. 

Figure 9. Sensitivity variations of In-doped Ti02 semiconductor sensor with NOx concentration[25].

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