Sensitizer-activator distances

Figure 11. The average sensitizer-activator distances vs. the concentration of the activator /-[SV[So] for Cu(I)Y exposed to oxygen. and [S]/[S ]...

F Fresnel number min minimum sensitizer-activator distance... 

Thus, the critical interaction distance is the sensitizer-activator separation for which the transfer rate is equal to the intrinsic decay rate. 

Surface activity concentration (external contamination) (Bq/m ) or equivalent Alpha monitoring Scintillation or proportional counter Inexpensive Rapid Immediate results Not radionuclide-specific Very sensitive to distance from surface to monitor Monitors are fragile Not very accurate Requires trained p son-nel... 

Here pis the quantum efficiency of the sensitizer (ti = Tp/xp = l/3forpentacene)in the O4 site of p-terphenyl at 4 K, n is the index of refraction (n = 1.7 for the p-terphenyl crystal), and Na is the Avogadro s number. The integral in (H9) is calculated from the normalized fluorescence spectrum/(v) and the decadic molar extinction coefficient e(v) of pentacene at O4 site. The critical interaction distance is the sensitizer-activator separation for which the transfer rate is equal to the intrinsic decay time. Although derived for low temperatures. Equation H9 is also vaUd for arbitrary temperatures. In fact, the temperature dependence of the resonant energy transfer rate is contained in the spectral overlap integral. 

The detector setup consists of four 256 x 256 pixel amorphous silicon technology sensor flat panels with 0.75 x 0.75 mm pixel size, having an active area of 192 x 192 mm [5j. These sensors are radiation sensitive up to 25 MeV and therefor well suited for detecting the LINAC radiation. The four devices are mounted onto a steel Irame each having the distance of one active area size from the other. With two vertical and two horizontal movements of the frame it is possible to scan a total area of about 0.8 x 0.8 m with 1024 x 1024 pixel during four independent measurements. 

Some studies of potential commercial significance have been made. For instance, deposition of catalyst some distance away from the pore mouth extends the catalyst s hfe when pore mouth deactivation occui s. Oxidation of CO in automobile exhausts is sensitive to the catalyst profile. For oxidation of propane the activity is eggshell > uniform > egg white. Nonuniform distributions have been found superior for hydrodemetaUation of petroleum and hydrodesulfuriza-tion with molybdenum and cobalt sulfides. Whether any commercial processes with programmed pore distribution of catalysts are actually in use is not mentioned in the recent extensive review of GavriUidis et al. (in Becker and Pereira, eds., Computer-Aided Design of Catalysts, Dekker, 1993, pp. 137-198), with the exception of monohthic automobile exhaust cleanup where the catalyst may be deposited some distance from the mouth of the pore and where perhaps a 25-percent longer life thereby may be attained. 

The scheme of the element is shown in Fig. 4.16. In order to increase variation of electric conductivity semiconductor film was deposited in the center of the plate, whereas activator was deposited at the plate edges at above specified distances through a mask. All stages of preparation were conducted in high vacuum ( 10" Torr). Sensitivity of such sensors to adsorption of hydrogen atoms at room at lower temperatures was about 10 - 10 at/cm, which corresponds to surface coverage of only 10-8 10-7% ( )... 

As we have seen above, FRET is a technique that provides precise information about distances between 10 and 100 A which is in the range of the size of biological molecules and proteins. Researchers have taken advantage of this feature and developed different strategies to synthesize FRET sensors that are able to follow in real time and with high sensitivity very diverse processes such as enzymatic activity, conformational change, or molecule-molecule interaction. The design of these FRET sensors is described below. 

One of the most characteristic features of FRET is its sensitive dependency on the fluorophore distance. This is advantageously used to evaluate structures and conformational changes of peptides, glycopeptides, and proteins among other molecules [164-166], The conformational change of the lipopeptide antibiotic daptomycin from an inactive linear form to a biological active cyclic form... 

To overcome this drawback, capillary sectorial fibres (Figure 11) were fabricated31. In this case part of the preform ground to the designed shape was inserted into a circularly symmetric silica tube and drawn. The active length of the sensor is defined by the distance between the input and output of the analyte produced in the capillary wall by special diamond tools. Despite promising results achieved, difficulties in the application of sensitive layers on the core surface remain a drawback of this kind of fibres and the... 

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