Limiting dilution experiment

The cell transfer limiting dilution experiments were initiated when T and B cell cooperation was not yet discovered, but in most of the experiments care was taken to ensure that only one kind of cell was limiting (Brown et al., 1966 Shearer et al., 1968 Bosma and Weiler, 1970). In recent years the method has been adapted to estimate the frequencies separately for B cells... 

The influence of the sensitivity of the assessors on AEDA has been studied [11], with the result that the differences in the FD factors determined by a group of six panellists amount to not more than two dilution steps (e.g. 64 and 256), implying that the key odorants in a given extract will undoubtedly be detected. However, to avoid falsification of the result by anosmia, AEDA of a sample should be independently performed by at least two assessors. As detailed in [6], odour threshold values of odorants can be determined by AEDA using a sensory internal standard, e.g. ( )-2-decenal. However, as shown in Table 16.6 these odour threshold values may vary by several orders of magnitude [8] owing to different properties of the stationary phases. Consequently, such effects will also influence the results of dilution experiments. Indeed, different FD factors were determined for 2-methyl-3-furanthiol on the stationary phases SE-54 and FFAP 2 and 2 , respectively. In contrast, 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone showed higher FD factors on FFAP than on SE-54 2 and 2, respectively. Consequently, FD factors should be determined on suitable GC capillaries [8]. However, the best method to overcome the limitations of GC-O and the dilution experiment is a sensory study of aroma models (Sect. 16.6.3). 

It is evident from Table 1 that certain limiting factors exist. For example, experiments with bromine-82 are limited to a duration of about one week because of the short half-life. At the other end of the scale, experiments with stable carbon-13 are limited to dilutions of less than x 500. Even with radioactive isotopes the maximum specific activity available may limit dilution though not to the same extent. Thus, chlorine-36 can stand dilutions up to x 107 but tritium can improve on this to a factor of x 1012. 

We limit our discussion to the application of these equations in NMR and UV-vis dilution experiments for the determination of monomer-dimer equilibria. 

With the use of IRMs, these false assumptions can be avoided and traceable isotope amount ratios can be generated. At present, however, only for a limited number of elements is an IRM available, as can be seen from Tables 6.1 and 6.2. Natural-like IRMs (Table 6.1) can be used to correct for mass discrimination, whereas enriched IRMs (Table 6.2) are mainly used in tracer studies and isotope dilution experiments. The enriched IRMs offer sufficient quality, but the number of elements covered is too low. This has been discussed at several meetings with the summarized outcome that several enriched isotopes have been exhausted... 

In our experience, any Drosophila cell line can be cloned by limiting dilution (in 96-well plates) provided the growth of isolated cells is supported by the presence of a suspension of X-rayed feeder cells. Some fines (notably S2) can be cloned in soft agar, at a considerable saving of labor and money. Detailed procedures for both techniques have been published recently (Cherbas et al. 1994 Cherbas and Cherbas 1998). 

In contrast to the results obtained in animal systems, earher studies suggested that free hydroxyproline may serve as precursor of the hydroxyprohne in actinomycin I (Katz and Goss, 1958, 1959 Katz, Prockop and Udenfriend, 1962). The addition of C-hydroxyproline enhanced formation of actinomycin I suggesting that a direct incorporation of hydroxyprohne could take place (Katz and Goss, 1958, 1959). Isotope dilution experiments have also provided further evidence for this hypothesis (Katz, Prockop and Udenfriend, 1962). In an experiment in which L-proline- C and unlabeled hydroxyproline were supphed to S. antibioticus it was determined that there was a 6-fold dilution of C-label in the hydroxyproline of actinomycin I. Somewhat more direct evidence was obtained with C-hydroxy-L-proline which was incorporated into actinomycin I as peptide-bound hydroxyproline to an appreciable extent (Katz, Prockop and Udenfriend, 1962). The efficiency of incorporation into actinomycin I actually approached that observed in some experiments with L-proline- C. As only a limited amount of C-label was present in the proline (or oxoproline) of actinomycins I, IV and V, it was postulated that free proline is converted to free hydroxyproline which is then incorporated into the antibiotic peptide. If this postulate is true, then the microbial system may differ somewhat from animal... 

Rowell and co-workers [62-64] have developed an electrophoretic fingerprint to uniquely characterize the properties of charged colloidal particles. They present contour diagrams of the electrophoretic mobility as a function of the suspension pH and specific conductance, pX. These fingerprints illustrate anomalies and specific characteristics of the charged colloidal surface. A more sophisticated electroacoustic measurement provides the particle size distribution and potential in a polydisperse suspension. Not limited to dilute suspensions, in this experiment, one characterizes the sonic waves generated by the motion of particles in an alternating electric field. O Brien and co-workers have an excellent review of this technique [65]. 

PR valve risers in flammable service should also be sized such that exit velocities are at least 30 m/s under all foreseable contingencies (except fire) which would cause the valve to release. On the basis of experimental work and plant experience, this minimum velocity, in conjunction with the riser elevation requirements, has been shown to ensure effective dispersion. Entrainment of air and dilution result in a limited flammable zone, with a negligible probability of this zone reaching any equipment which could constimte an ignition source. 

Binary (vapor + liquid) equilibria studies involve the determination of / as a function of composition. the mole fraction in the liquid phase. Of special interest is the dependence of/ on composition in the limit of infinite dilution. In the examples which follow, equilibrium vapor pressures, p,. are measured and described. These vapor pressures can be corrected to vapor fugacities using the techniques described in the previous section. As stated earlier, at the low pressures involved in most experiments, the difference between p, and / is very small, and we will ignore it unless a specific application requires a differentiation between the two. 

The creation of a steady flame hole was previously carried out by Fiou et al. [36]. In their experiments, a steady-annular premixed edge flame was formed by diluting the inner mixture below the flammability limit, for both methane/air and propane/air mixtures. They found that a stable flame hole was established when the outer mixture composition was near stoichiometry. Their focus, however, was on the premixed flame interaction, rather than on the edge-flame formation, extinction, or propagation. 

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