Critical experiments

Documentation of experimental method so that work can be reproduced at a later time Appropriate data handling statistical methods conclusions based on fact, supportable by data Define and execute critical experiments to prove or disprove hypothesis Mechanistic or fundamental interpretation of data preferred Communication of Conclusions to Incorporate Technical Learning in Organization Experimental W rk Done in Support of New or Existing Processes Should be Captured in Process Models... 

Vapor space velocities normally should not exceed 100% of critical experience demonstrates that this keeps liquid entrainment into the flare line within acceptable limits. However, a velocity of 175% of critical is permitted when one is applyingthe 1.5 times Design Pressure Rule to remote contingencies,... 

In 1952, Konrad Bloch and Robert Langdon showed conclusively that labeled squalene is synthesized rapidly from labeled acetate and also that cholesterol is derived from squalene. Langdon, a graduate student of Bloch s, performed the critical experiments in Bloch s laboratory at the University of Chicago, while Bloch spent the summer in Bermuda attempting to demonstrate that radioactively labeled squalene would be converted to cholesterol in shark livers. As Bloch himself admitted, All I was able to learn was that sharks of manageable length are very difficult to catch and their oily livers impossible to slice (Bloch, 1987). 

Leonzio C, Massi A. 1989. Metal biomonitoring in bird eggs. A critical experiment. Bull Environ Contam Toxicol 43 402 06. 

Nasmyth It is definitely compromised in yeast. But thankfully they are not completely dead, which allowed Doug Koshland and us to do the critical experiment which really pinpointed securin as the key target. In this we took an APC mutant, knocked out securin, and showed that then they would separate sister chromatids. 

Step 1 is fundamentally an SN2 reaction (kinetics related to structural variations of the reactants,16 8 retention of stereochemistry at phosphorus912), except in those instances wherein a particularly stable carbocation is produced from the haloalkane component.13 A critical experiment concerned with verification of the Sn2 character of Step 1 by inversion of configuration at the carbon from which the leaving group is displaced was inconclusive because elimination rather than substitution occurred with the chiral secondary haloalkane used.14 An alternative experiment suggested by us in our prior review using a chiral primary substrate apparently has not yet been performed.2... 

The in vitro procedure was tested in "critical" experiments designed to make direct comparisons of in vivo and in vitro estimates of exchangeability and potential bioavailability and to test the use of in vitro exchangeability values in in vivo experiments. (8). Three foods which were expected to show different levels of calcium solubility and exchangeability, collards, soybeans and spinach, were intrinsically labeled with 45Ca in nutrient solution culture. They were used together with 47 Ca as an extrinsic label in both in vitro and in vivo experiments. 

From the above, it is evident that every photochemical system must be carefully analysed in order to establish the nature of the process of spin adduct formation. Not all systems have the inbuilt diagnostic features of the fluoride or carboxylate nucleophiles, and it must therefore be accepted that mechanistic certainty will be difficult to attain. It also must be remembered that many studies in the past were designed without regard to the inverted spin trapping mechanism and are difficult to judge owing to lack of critical experiments to test this particular aspect. 

However, the amount of error in the data is not generally the limiting factor in data interpretation. Rather, the locations at which the data are taken most severely hinder progress toward a mechanistic model. Reference to Fig. 1 indicates that the decision between the dual- and single-site models would be quite difficult, even with very little error of measurement, if data are taken only in the 2- to 10-atm range. However, quite substantial error can be tolerated if the data lie above 15 atm total pressure (assuming data can be taken here). Techniques are presented that will seek out such critical experiments to be run (Section VII). 

By slowly increasing the complexity of the models in this fashion, it was hoped that a model could be obtained that was just sufficiently complex to allow an adequate fit of the data. This conscious attempt to select a model that satisfies the criteria of adequate data representation and of minimum number of parameters has been called the principle of parsimonious parameterization. It can be seen from the table that the residual mean squares progressively decrease until entry 4. Then, in spite of the increased model complexity and increased number of parameters, a better fit of the data is not obtained. If the reaction order for the naphthalene decomposition is estimated, as in entry 5, the estimate is not incompatible with the unity order of entry 4. If an additional step is added as in entry 6, no improvement of fit is obtained. Furthermore, the estimated parameter for that step is negative and poorly defined. Entry 7 shows yet another model that is compatible with the data. If further discrimination between these two remaining rival models is desired, additional experiments must be conducted, for example, by using the model discrimination designs discussed later. The critical experiments necessary for this discrimination are by no means obvious (see Section VII). 

Surprisingly, the critical experiment has been done infrequently over the last one-half of a century The requirements for an experiment that truly speaks to the issue at hand are that one be able to see the results of addition of both spin states of a single carbene, and these requirements rarely have been met. For example, the direct irradiation of methyl diazomalonate leads to the stereospecific addition expected of a singlet carbene, whereas the photosensitized decomposition of the diazo compound leads to formation of the triplet carbene and loss of the stereochemical relationship originally present in the reacting alkene. Rotational equilibration in the intermediate seems to be complete, as it makes no significant difference whether cis or trans alkene is used as starting material (Scheme 7.9). ... 

Simulation of the process with analytical models can be used to evaluate the effects of changes in process parameters, providing the limiting assumptions of the model are noted [16]. These parametric studies can then be used to select critical experiments for selecting a cure cycle or to establish rules for process-cycle development [17]. If the simulation is true enough to the actual behavior of the material and processing vessel and provides the necessary predictions of material quality, it can even be used to select a cure cycle [15,18]. 

Some critical experiments of the type described above were repeated, and similar results were obtained. The observations are consistent with the following stoichiometry for the initial reaction ... 

In the preceding paragraphs we have discussed bifunctional catalysis from the standpoint of the nature of the catalyst surface as well as the kinds of reactions which take place and have summarized the results of certain critical experiments from which a mechanistic picture has evolved. With this background in mind, we will now discuss the results of kinetic studies in the following sections. 

In all the preceding evaluations, it is prudent to first employ a redox system that is known to be reversible and free from the complications of coupled chemical reactions and adsorption. Deficiencies in the electronics and/or cell design will thus be revealed before the critical experiments are begun. Typical... 

Type A treatment relies on the effect of the overwhelming psychedelic experience. Dosage levels too low to induce the critical experience of surrender leave the individual trapped in his pretensions. Massive doses may release material too fast and too heavily charged with emotion for the subject to find symbols to encode the experience until so late in the session that much is forgotten and repressed again. Very heavy demands are placed on the therapist during the ses-... 

Figure 1. Critical experiments that are the foundation of hormonal control of plant growth. (Figure modified from Boysen Jensen et al., 1936)...

Further revealing information is obtained from individual monitoring of the polarization evolution profiles of the separate components of the CIDEP spectrum. These are given in Figure 4b. The results clearly indicate that the "new" radical is the primary intermediate, formed before the phenacyl radical. Furthermore, the relative relaxation rate of the spin polarization of the phenacyl radical is faster than that of the "new" radical. A final critical experiment is that when very dry acetonitrile was used as solvent, no CIDEP observations could be obtained for any radicals. From all these observations we are now ready to formulate the primary phototriplet reactions mechanism to account for all these facts. 

Formulation of a model represents an effective way to think through all of these questions, and to define the conditions for the necessary critical experiments. 

Thus, the critical experiment to distinguish whether the inhibitor is adsorbing on the metal or on a protective layer is to find out whether the inhibitor- graph is parabolic. The distinguishing experiment was done with 14C labeled phenylalanine. Figure 12.54 shows the potential dependence of the adsorption of this compound on platinum (to show how the adsorption of this substance behaves on a metal) and on Fe in contact with a pH 3.8 phosphate buffer. 

Abstract. A review is given of the latest adjustment of the values of the fundamental constants. The new values are recommended by the Committee on Data for Science and Technology (CODATA) for international use. Most of the fundamental constants are obtained by the comparison of the results of critical experiments and the corresponding theoretical expressions based on quantum electrodynamics (QED). An important case is the Rydberg constant which is determined primarily by precise frequency measurements in hydrogen and deuterium. 

The 1998 adjustment of the values of the fundamental physical constants has been carried out by the authors under the auspices of the CODATA Task Group on Fundamental Constants [1,2]. The purpose of the adjustment is to determine best values of various fundamental constants such as the fine-structure constant, Rydberg constant, Avogadro constant, Planck constant, electron mass, muon mass, as well as many others, that provide the greatest consistency among the most critical experiments based on relationships derived from condensed matter theory and quantum electrodynamics (QED) theory. The 1998 CODATA recommended values of the constants also may be found on the Web at physics.nist.gov/constants. 

---