Experimental conditions, discriminating

Extension of this research was then delayed until two of us had returned to New Zealand. One of the first jobs of Tasker, a PhD student from Brisbane, was to use 3H-labeling methods to examine epimerization. At that time we were under the impression that reprotonation of carbanion intermediates would be diffusion controlled, as was subsequently reported for phenylglycine in phosphate buffers (18), so that no isotopic discrimination against 3H would be present. But then Wautier et al. reported (6) the complete loss of chirality in [Co(tren)(AA-(S)-AA OMe)]3+, prepared by treating [Co(tren)((S)-AAOMe)]3+ (AA = Ala, Leu) generated in situ in MeOH with (S)-AA OMe (AA = Leu, His, Ala, Val), although their reaction times and temperatures (1-15 h sometimes 35-50°C) and other experimental conditions ([Co(III)] —0.1 M L/V-ethylmorpholine salt of p-toluene sul-... 

We usually seek to distinguish between two possibilities (a) the null hypothesis—a conjecture that the observed set of results arises simply from the random effects of uncontrolled variables and (b) the alternative hypothesis (or research hypothesis)—a trial idea about how certain factors determine the outcome of an experiment. We often begin by considering theoretical arguments that can help us decide how two rival models yield nonisomorphic (i.e., characteristically different) features that may be observable under a certain set of imposed experimental conditions. In the latter case, the null hypothesis is that the observed differences are again haphazard outcomes of random behavior, and the alternative hypothesis is that the nonisomorphic feature(s) is (are) useful in discriminating between the two models. 

Lastly, it is desirable that parameters are able to discriminate between positive and negative conditions in a variety of experimental conditions. In other words they should be robust and reproducible. For this purpose, the Pearson correlation coefficient between all experimental repeats using control wells is calculated. Robust parameters have high Pearson correlation coefficients (above 0.7) in pairwise comparisons of experimental repeats. For this analysis we have developed another R template in KNIME to calculate the Pearson correlation coefficient between experimental runs. 

The ability to determine which copolymerization model best describes the behavior of a particular comonomer pair depends on the quality of the experimental data. There are many reports in the literature where different workers conclude that a different model describes the same comonomer pair. This occurs when the accuracy and precision of the composition data are insufficient to easily discriminate between the different models or composition data are not obtained over a wide range of experimental conditions (feed composition, monomer concentration, temperature). There are comonomer pairs where the behavior is not sufficiently extreme in terms of depropagation or complex participation or penultimate effect such that even with the best composition data it may not be possible to conclude that only one model fits the composition data [Hill et al., 1985 Moad et al., 1989]. 

Certain SEC applications solicit specific experimental conditions. The most common reason is the limited sample solubility. In this case, special solvents or increased temperature are inavoid-able. A possibility to improve sample solubility and quality of eluent offer multicomponent solvents (Sections 16.2.2 and 16.8.2). The selectivity of polymer separation by SEC drops with the deteriorating eluent quality due to decreasing differences in the hydrodynamic volume of macromolecules with different molar masses. The system peaks appear on the chromatograms obtained with mixed eluents due to preferential solvation of sample molecules (Sections 16.3.2 and 16.3.3). The multicomponent eluents may create system peaks also as a result of the (preferential) sorption of their components within column packing [144,145]. The extent of preferential sorption is often sensitive toward pressure variations [69,70,146-149]. Even if the specific detectors are used, which do not see the eluent composition changes, it is necessary to discriminate the bulk sample solvent from the SEC separated macromolecules otherwise the determined molecular characteristics can be affected. This is especially important if the analyzed polymer contains a tail of fractions possessing lower molar masses (Sections 16.4.4 and 16.4.5). 

Clearly ni and ni are only real if the discriminant under the square root sign in (10.49) is positive for the experimental conditions (i.e. the values of P, H, and k). Thus we require that... 

The present sensor could easily discriminate between some kinds of commercial drinks such as coffee, beer and aqueous ionic drinks (Figure 11) [22], Since the standard deviations were 2 mV at maximum in this experimental condition, these three output patterns are definitely different. If the data are accumulated in the computer, any food can be easily discriminated. Furthermore, the taste quality can also be described quantitatively by the method mentioned below. In biological systems, patterns of frequency of nerve excitation may be fed into the brain, and then foods are distinguished and their tastes are recognized [4-8]. Thus, the quality control of foods becomes possible using the taste sensor, which has a mechanism of information processing similar to biological systems. 

There is a notorious difference between the analytical signal obtained for a 3.03 nM solution of the complementary target strand and three-base mismatch strand. In stringent experimental conditions (2 x SSC containing 50% formamide), the analytical signals are 47.61 and 3.96 pA, respectively, when hybridisation takes place for 1 h. Therefore, a 100% discrimination is achieved. 

Table 1 (48a,b) shows the 24 hr results of the test described above on phenylbutazone. Copper degraded phenylbutazone both as a salt and as acetyl acetonate. Iron was less aggressive, and the free salt was stronger than the complex. The degradation products were 4-hydroxy- and 4-hydroperoxy-phenylbutazone, the known oxidation impurities. The susceptibility of phenylbutazone to metal oxidation can be attributed to activation of the hydrogen on C-4 by the adjacent carbonyls. Selegiline hydrochloride, a stable compound, was not oxidized under the same conditions. This confirms the discriminating power of the experimental conditions. 

Note, however, that, in the case of fundamental models, there is not always a need to discriminate among rival models since, often, only a single model has been built up. Furthermore, the best criterion of the quality of a model is the consistency of fundamental parameter estimates with other values obtained by means of several methods under a large range of experimental conditions. Let us not be misled about the principle enemy the systematic errors both in experiments and in reaction and reactor models. 

For such treated samples it is not easy to discriminate between two possible effects of dealumination, namely, the removal of some acid sites and the decrease in microporosity due to the deposition of aluminum-containing debris in the pores. Thus, hydrothermally dealuminated FER, hydro thermally dealuminated acid-washed FER. acid-washed FER, and CsFER were compared under the same experimental conditions (62). The results indicate the following order of isobutylene selectivities untreated FER < acid-treated FER < hydrothermally treated FER < hydrothermally acid-treated FER < CsFER 61). These results, obtained with noncoked catalysts, reinforce the interpretation in terms of shape selectivity. The hydrothermally acid-treated sample has acid sites located only in the micropores, and the aluminium debris in the micropores creates an additional constraint playing a role identical to that of Cs" in FER. 

There is a large body of experimental evidence which has been interpreted to fit one or more of these models, but there is still no consensus, in part owing to the different experimental conditions. The most recent data suggest that bending and binding occur at the same time, and that there appear to be two intermediates [60]. Also, correctly pre-bent [61] or more flexible DNA is bound better by TBP, and dissociates more slowly [8,62]. A structural model for these intermediates would serve well in the discrimination of alternatives. 

We evaluated the performance of different catalysts under two distinct experimental conditions (1) under reactor conditions (Ri), where the main objective of the catalyst is to hydrolyze COS and particularly CS2 and (2) under reactor conditions (R2), where the Claus reaction (Eq. 3) is more discriminating for a catalyst evaluation. 

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