Fluorescence ratio profiles

Gaussian Laser Profile-Voigt Atom Profile. This case turns out to be a better approximation of our experimental situation, i.e., the laser FWHM is fairly broad compared to the absorption line width and the absorption profile of atoms in an atmospheric combustion flame is described by a Voigt profile. Here the laser is assumed to have a Gaussian spectral profile as well as a Gaussian atomic absorption profile. In this case, convolution of two Gaussian functions is still a Gaussian function. Evaluation of the ratio n2/nT, and the fluorescence radiance. Bp, allows determination of the half width of the fluorescence excitation profile, 6X... 

Martin, G. R. Jain, R. K. Noninvasive measurement of interstital pH profiles in normal and neoplastic tissue using fluorescence ratio imaging microscopy. Cancer Res. 1994, 54,... 

Different fluorescence response profiles were observed for several NAC s, such as 1,3,5-trinitrotoluene (TNT) and 1,3-dinitrobenzene (DNB), despite their similar structures. These responses were monitored at low concentrations of the NAC vapours (ca. 5 ppb) and at short vapour exposure times (less than 200 ms). The detection of such low concentrations is possible since we are able to measure simultaneously the responses of a high number of individual sensors and sum their responses, thereby increasing the S/N ratio. Theoretically this ratio increases by vl, where n is the number of sensors analyzed. Therefore, by combining the responses of a large number of individual beads (1000 beads), the noise is essentially removed and low concentrations of analytes can be detected (Figure 7). 

Fig. 3-12. Vertical distribution of CIO, HC1, and HF in the stratosphere. Left Filled circles give the averages of eight altitude profiles for CIO measured in 1976-1979 by in situ resonance fluorescence the envelope indicates the range of values (Weinstock etai, 1981) two additional high-mixing-ratio profiles are not included. The open circles are from balloon-borne infrared remote measurements by Waters et al. (1981) and Menzies (1983). Center The envelope encompasses observational data for HC1 obtained by balloon-borne infrared measurement techniques (Farmer et al, 1980 Buijs, 1980 Raper et al., 1977 Eyre and Roscoe, 1977 Williams et al., 1976 Zander, 1981) filled circles represent more recent preliminary data cited...

In a second study, they evaluated the interfacial thickness of twopoly(isoprene-b-methyl methacrylate) block copolymers (Pl-PMMA) using the same approach. Small-angle X-ray scattering experiments showed that films of the mixed diblock copolymers have a lamellar morphology with a spacing that varies with composition from 24 to 26 nm. Fluorescence decay profiles from these films were analyzed in terms of an energy transfer model that takes into account the distribution of junctions across the interface and calculated an interface thickness of 1.6 + — 0.1 nm. This value was independent of the acceptor/donor ratio (i.e., the acceptor concentration) in the films. 

This is illustrated with a fluorescence intensity profile across several features (Figure 4, inset). It is known from measurements with optical waveguide lightmode spectroscopy (OWLS) that below 1 ng/cm of protein is adsorbed on PLL-g-PEG, while 50 3 ng/cm of streptavidin adsorbs on the DDP SAM (data not shown), resulting in a selectivity ratio (protein adsorbed on liOj DDP over protein adsorbed on Si02/PLL-g-PEG) of at least 50. The fluorescence intensity values quoted above yield a contrast ratio of 100. The difference is likely to be caused by the lower sensitivity of OWLS. 

Calculations of the variations expected in the fluorescent-yield (FY) profiles as a function of the distribution model parameters are shown in Figure 7.19. When the species of interest resides predominantly at the solid surface, the FY profile shows a maximum at the critical angle for total external reflection. As the ratio of the surface-bound species to the total number of species in the solution volume adjacent to the surface decreases, the FY distribution broadens at the low angles. A similar effect is noted when a diffuse layer accumulation arises due to an interfacial electrostatic potential. 

The analysis of the temporal fluorescence profiles in Figs. 2.17a and 2.17b shows that the kinetic scheme used is a fairly good description at least for the case shown The ratio of the preexponential factors for rise and decay parts of the A fluorescence is 0.96, thus very close to the theoretical value of 1.0 predicted by Eq. (2.29), and the decay time of the B fluorescence is similar to the rise time of the A fluorescence. 

Figure 3.22. Model relaxation of the surface excitons created inside or near the threshold of a two-particle-state continuum (illustrated for the 390-cm 1 mode). After excitation (1) at the energy Ekh + 390 cm. a two-particle state is created (2) by fission. Then the exciton may relax along two competing paths an intrasurface channel (3) leading to emission, and a nonradiative channel (3 ) to the bulk (eventually to its fluorescence), with respective probabilities ris and rB. Therefore, the surface emission efficiency depends on the ratio rjrB, which determines the observed profile. When the excitation occurs at exactly 390 cm 1 above the detection, we observe the very narrow Raman peak.

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