Practical Tips

The TCSPC-FCS technique can also be used in conjunction with a continuous laser. Of course, in this case the measurement does not deliver a meaningful miero time, and no lifetime data are obtained. Because the TCSPC module needs a synchronisation pulse to finish the time measurement for a recorded photon, an artificial stop pulse must be provided. This can be the delayed detector pulse itself or a signal from a pulse generator see Fig. 5.116. 

Compared to fluorescence decay measurements, the effieieney of FCS measurements is relatively low. For a given number of photons, N, the SNR of a fluorescence decay measurement is proportional to N, whereas the SNR of FCS is proportional to N itself This somewhat surprising behaviour results from by the fact that two photons are needed to obtain one maerotime eoineidenee in the eorre-lation histogram. The strong dependenee of the SNR on the number of deteeted photons makes detection efficiency an important issue in FCS. 

Most FCS setups therefore use single photon avalanehe photodiodes [323,424], usually SPCM-AQR detectors from Perkin Elmer [408]. These deteetors have a quantum efficiency that reaches 80% at 800 nm. However, single photon APDs often have a timing delay and transit time jitter dependent on wavelength and count rate. The changes can be of the order of 1 ns. Recording a fluorescence decay curve under this condition delivers questionable results. 

Timing problems can be avoided by using PMTs with high-efficieney GaAsP photocathodes, such as the Hamamatsu H7422-40 module [214]. The modules have a stable and almost wavelength-independent transit time spread of about 300 ps duration (see Sect. 6.4.2 page 245). The quantum efficiency reaches 40% at 

550 nm. Below 500 nm it is higher than for a single photon APD. Another benefit of a PMT is the large cathode area. In two-photon FCS the light emitted at the back of the sample can be collected by the condenser lens of the microscope and directed to a second PMT. The poor optical quality of the condenser precludes focusing on an APD, but is no problem for the PMT. 

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Maze. R. W. Hydrocarbon Process., 46(2) (1967) 123. Practical tips on cooling tower sizing. 

For comparable diffusion coefficients of the target solute in the two phases and nonlimiting transfer kinetics, systems characterized by different should be resolvable on the basis of transient and steady-state current responses to a value of up to 50 at practical tip-interface separations. If the diffusion coefficient in phase 2 becomes lower than that in phase 1, diffusion in phase 2 will be partly limiting at even higher values of K. On the other hand, as the value of y increases or interfacial kinetics become increasingly limiting, lower values of suffice for the constant-composition assumption for phase 2 to be valid. 

Braun, S.S. Power Recovery Pays off at Shell Oil, Oil and Gas Journal, May 21, 1973, p. 129. Abadie, V.H. Turboexpanders Recover Energy, Hydrocarbon Processing, July 1973, p. 93. Casto, L.V. Practical Tips on Designing Turbine-Mixer Systems, Chemical Engineering, Jan. 10,... 

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A REVIEW OF NATURAL AND NON-NATURAL CATALYSTS IN SYNTHETIC ORGANIC CHEMISTRY PRACTICAL TIPS FOR SOME IMPORTANT OXIDATION AND REDUCTION REACTIONS... 

Another practical tip to find out how a business really works, interview the people who do it and not their managers, who don t know the half of it. And don t believe what people say they do Watch them doing it. It usually takes several visits to do the job properly. 

Give exact practical details of the proposed procedure (use separate sheets if necessary). You should include any practical tips/hints gained through personal experience. 

Wagner J. (2001). Membrane Filtration Handbook Practical Tips and Hints. Available at http // www.osmonics.com/Ubrary/1229223-%20Lit-%20Membiane%20Filtration%20Handbook. pdf accessed 12/02/2006. 

Particularly in the cases of hydroxyacetylenes, the question "How many extractions with Et20 have to be earned out may arise. The following practical tip may be useful. Take a small (2 ml) sample from the extract with a Pasteur pipet and allow the solution to flow along a glass stopper. Further extraction is superfluous when, after the ether has evaporated, no residue is visible on the ground glass. 

Practical Tips on Cooling-Tower Sizing Maze, R. W. 

Answering these questions and understanding the uncertainties associated with sampling and analysis is crucial for developing any data collection design. Several practical tips for conducting the DQO process are offered in the box on the next page. 

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Practical Tips Sampling into prcwcighcd vials... 

Use all of the practical tips offered for sampling into preweighed vials. 

Practical Tips Preservation with chemicals in the field... 

Practical Tips Surface sampling with wipes... 

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