Possible Pitfalls

Unfortunately, it s not quite as simple as that. In the next chapter, we ll delve a little deeper and have a look at some possible pitfalls you may encounter in more complex spectra. 

Thus, physical scientists have become increasingly aware of the need to define concepts in terms of operations instead of relying on inmitive feelings of a priori recognition. To avoid possible pitfalls in thermodynamic applications, it is desirable that all thermal and energy concepts likewise be approached with an operational attitude. The use of operational definitions is particularly important in a phenomenological science such as thermodynamics. 

A probabilistic risk assessment (PRA) deals with many types of uncertainties. In addition to the uncertainties associated with the model itself and model input, there is also the meta-uncertainty about whether the entire PRA process has been performed properly. Employment of sophisticated mathematical and statistical methods may easily convey the false impression of accuracy, especially when numerical results are presented with a high number of significant figures. But those who produce PR As, and those who evaluate them, should exert caution there are many possible pitfalls, traps, and potential swindles that can arise. Because of the potential for generating seemingly correct results that are far from the intended model of reality, it is imperative that the PRA practitioner carefully evaluates not only model input data but also the assumptions used in the PRA, the model itself, and the calculations inherent within the model. This chapter presents information on performing PRA in a manner that will minimize the introduction of errors associated with the PRA process. 

The Genetic Modification of NP Pathways—Possible Opportunities and Possible Pitfalls... 

The presence of symmetry in a molecule can be used to great advantage in electronic structure calculations, although some care is required to avoid possible pitfalls that are simultaneously introduced (Appendix B provides a brief overview of nomenclature (e.g., the term irrep . 

Price Fixing of the patented item, while still in doubt in certain limited respects as to how far a licensor or patent owner can go in pursuing the practice, is not recommended at all, because of many possible pitfalls. 

A plant survey is normally a once-only opportunity to investigate the potential for conducting future water treatment business. Therefore it should not be undertaken lightly or at the first chance that arises. It is far better to begin to develop some form of loose business relationship first. This provides both parties with some time to consider what information may be necessary to obtain, to explore what possible pitfalls may exist, and to plan for them in advance (and whether the parties involved could work together). 

The investigator should be aware of a few possible pitfalls in binding studies and other assays. First, the reagent should be pure. This is of the utmost importance if the photoaffinity label is a derivative of the natural ligand and turns out to be less potent in its biological activity. In numerous cases where a derivative has appeared to be (say one hundred times) less active than its precursor, it has not been shown that the precursor was not a contaminant (say 1 %) of the derivative which was actually completely... 

Wilhelm, K.P. Possible pitfalls in hydration measurements. Curr. Probl. Dermatol. 1998 26 223-234. 

It is concluded from the foregoing considerations that pyridine may successfully be applied as a specific poison, provided the possible pitfalls are carefully kept in mind. The lower basicity of pyridine as compared to ammonia renders its chemisorption more selective. However, its basicity is in most cases still much higher than that of the commonly used reactants, so that one is usually able to determine an upper limit for the number of active sites by pyridine poisoning (239). On the other hand, the hardness of reactants or reaction products may be comparable with that of pyridine [e.g., dehydration of alcohols (47)] the poison will then be partially displaced. The molecular size of pyridine may bring about difficulties, since it restricts the accessibility of pyridine to narrow pores or even the approach to an adsorption site (214). In favorable cases, however, steric effects may be utilized to improve the specificity of poisoning (35, 36,241). 

With the various experimental techniques, the actual measurement concerns product ions after they have been extracted from the source. That is to say, the decomposition occurs in a source before acceleration, but what is actually measured is translational energy after the product ion has been accelerated. To be still more precise, it is, in most cases, the distribution of the component of velocity along the axis of the mass spectrometer (i.e. in the direction in which the ions were accelerated out of the source) which is, in effect, measured. The measured quantity is, therefore, distinct from the translational energy distribution of the product ion (called the laboratory distribution ) as it was upon its formation in the source (i.e. before acceleration). The measured distribution needs to be analysed to obtain the laboratory distribution. Working with means or averages is much simpler, but there are possible pitfalls (see the discussion of the time-of-flight technique below). 

Klahn M, Braun-Sand S, Rosta E, Warshel A (2005) On possible pitfalls in ab initio quantum mechanics/molecular mechanics minimization approaches for studies of enzymatic reactions. J. Phys. Chem. B 109 15645-15650... 

In this part of the book we give practical advice on how to apply molecular mechanics to problems involving metal complexes. Chapter 16 is a short introduction that gives advice on which model and force field should be chosen, how to interpret, use and describe the results and how to avoid possible pitfalls. Chapter 17 is a tutorial. Using the software included in this book and a computer with Microsoft Windows the reader can learn most of the methods and techniques presented in this book. 

Future applications of the DFT based hfcc calculations will involve extending the sets of systems into areas such as surface chemistry, biophysics, and large transition metal complexes, where MRCI approaches again will serve as an extremely important tool for calibrating the calculations of the larger systems, to reveal possible pitfalls and explain deviations when these occur. 

This is only a short list of possible pitfalls of the use of kinetic rate expressions in practice. Generally it is wise practice to test a catalyst experimentally before using available rate expressions (Chapter 5). The following gives a few examples to give weight to the above remarks. 

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