Potential Pitfalls

From one force held to the next, the balance of energy terms may be different. For example, one force held might use a strong van der Waals potential and no electrostatic interaction, while another force held uses a weaker van der Waals potential plus a charge term. Even when the same terms are present, different charge-assignment algorithms yield systematic differences in results and the van der Waals term may be different to account for this. 

When the same energy terms are used in two force helds, it may be acceptable to transfer bond-stretching and angle-bending terms. These are fairly stiff motions that do not change excessively. The force constants for these terms vary between force helds, much more than the unstrained lengths and angles. 

Transferring torsional and nonbonded terms between force helds is much less reliable. These are lower-energy terms that are much more interdependent. It is quite common to hnd force helds with signihcantly different parameters for these contributions, even when the exact same equations are used. 

Atoms with unusual hybridizations can be particularly dihicult to include. Most organic force helds describe atoms with hybridizations whose bond angles are all equivalent (i.e., sp, sp, and sp hybridizations with bond angles of 180, 120, and 109.5°, respectively). In contrast to this, a square planar atom will have some bond angles of 90° and some angles of 180°. In this case, it may be necessary to dehne the bond and angle terms manually, modify the software, or hold the bond angles hxed in the calculation. 

---

Potential Pitfalls with Free Energy Calculations... 

It is hoped that this section will give the reader a better appreciation of the range of ionic liquids that have already been prepared, as well as a summary of the main techniques involved and the potential pitfalls. While the basic chemistry involved is relatively straightforward, the preparation of ionic liquids of known purity may be less easily achieved, and it is hoped that the ideas given here may be of assistance to the reader. It should also be noted that many of the more widely used ionic liquids are now commercially available from a range of suppliers, including some specializing in the synthesis of ionic liquids [53]. 

The main problem related to the use of pseudopotentials in studies of solids under pressure is to make sure that the overlap of ionic cores does not increase significantly when interatomic distances decrease. The present study is certainly not affected by this potential pitfall since Ti-O distances typically change by no more than 0.1 A over the pressure range investigated. However, theoretical studies of fluorite and related phases at pressures of around 100 GPa should be performed with added caution. 

A potential pitfall with stop-time experiments comes with temporal instability of responses. When a steady-state sustained response is observed with time, then a linear portion of the production of reporter can be found (see Figure 5.15b). However, if there is desensitization or any other process that makes the temporal responsiveness of the system change the area under the curve will not assume the linear character seen with sustained equilibrium reactions. For example, Figure 5.16 shows a case where the production of cyclic AMP with time is transient. Under these circumstances, the area under the curve does not assume linearity. Moreover, if the desensitization is linked to the strength of signal (i.e., becomes more prominent at higher stimulations) the dose-response relationship may be lost. Figure 5.16 shows a stop-time reaction dose-response curve to a temporally stable system and a temporally unstable system where the desensitization is linked to the... 

MLR is the most widely used of the QSAR modeling techniques. Walker et al. [15] have published guidelines for the development and use of MLR-based QSARs, and Cronin and Schultz [41] have discussed their potential pitfalls. 

It is essential to have high-quality data in place for interoperable systems to function efficiently. Standard data structures can only be used to full advantage if they are combined with standard terminology for values populating a data element. Yet there are many potential pitfalls in data collection and configuration for analysis. Some of the more common pitfalls are discussed here, but this list is by no means comprehensive. 

The carryover effect is only one type of issue that may complicate the interpretation of results from a cross-over study. A more complete description of the potential pitfalls in the analysis of cross-over studies is beyond the scope of this chapter. The reader should simply be aware that, although cross-over studies may be less expensive to conduct than parallel trials initially, they also carry a higher risk of producing results that are fficult or impossible to interpret, thus requiring that the study be repeated to obtain clear results. 

Greenberg, B. D., McMahon, F. J. et al. (1998). Serotonin transporter candidate gene studies in affective disorders and personality promises and potential pitfalls. Mol. Psychiatry, 3(3), 186-9. 

W. L. Chiou, Potential pitfalls in the conventional pharmacokinetic studies Effects of the initial mixing of drug in blood and the pulmonary first-pass elimination, J. Pharmacokinet. Biopharm., 7, 527-536 (1979). 

Unfortunately, it is impossible to cover all the potential pitfalls that wait for the unwary. Many more will come to light in the following chapters but for now we will concentrate on supplying you with useful proton NMR chemical shift data... We have done this by collating various types of protons into convenient groups, but first, let s clear the wood from the trees and deal with commonly encountered solvents and impurities in the regularly used NMR solvents. 

However, FLIM measurements by both frequency and time domain using commercially available software suffers from variation in the measured lifetime from region to region in cells [36], which can be confusing. In the light of the potential pitfalls associated with each of the above-mentioned FRET techniques, potential protein associations should ideally be tested independently by a combination of two or more FRET-based methods in addition to biochemical techniques such as co-immunoprecipitations. 

The application of visible/infrared spectrometry (VIRS) in economic geology research Potential, pitfalls and practical procedures... 

A better understanding of the changes in surface structure during silylation is needed before the potential advantages of silylation of these mesoporous materials are realized. A potential pitfall in silylation reactions is the silylation of... 

As it can be seen, the investigations of heterogeneous chiral catalysts started in the late 1950s in Japan and has known a worldwide renaissance in the last few years. Because of a multitude of catalysts discovered and developed in the recent years, combinatorial methods have become an important focus of research in asymmetric catalysis [168,169], In the last few years, efficient techniques have been developed for the high throughput parallel screening of chiral catalysts [170-172], However, parallel screening based on product analysis has potential pitfalls, since the e.s. of a... 

In this chapter, we discuss how to perform meaningful tribological simulations by avoiding the potential pitfalls that were mentioned above. In the next section, some theoretical aspects of friction between solids will be explained. Then an overview of algorithms that have been used in the simulation of tribological phenomena is provided. Selected case studies will be presented in the last section. 

Reflection will show the potential pitfalls of either of these approaches. Neither is higher or better than the other. Direct doesn t mean quicker, nor does indirect mean that you reach the Goal incidentally. It comes down, in the end, to personal temperament and environment. Very, very few individuals are exclusively suited to one path or the other. Practitioners walking the direct path often use liturgical (ceremonial) devotions as part of their daily routine. Practitioners treading the indirect path find that states of consciousness, at first attained in ceremonial settings, later no longer need a ritual impetus to be experienced and that they can now enjoy these states by the direct path. 

This section explains the benefits of online and traditional paper applications. You will learn the potential pitfalls of each, and how to avoid them, as well as tips to ensure your application looks its best, no matter which submission method you choose. 

Some practical aspects of isotopic patterns as commonly observed in mass spectra should now be considered. Although it seems trivial, the first step is the recognition of an isotopic pattern as such, and especially for beginners this is not always easy. Especially if signals from compounds differing by two or four hydrogens are superimposed or if such a superimposition can not a priori be excluded, a careful stepwise check of the observed pattern has to be performed to avoid misinterpretation of mass spectral data. Similar care has to be taken when isotopically labeled compounds are involved. Next, potential pitfalls for the novice, the correct treatment, and the benefits of isotopic patterns are discussed. 

Eliminate potential pitfalls such as air bubbles in the sampling syringe, tightly sealed vial closures, an overly fast sample dosing speed for viscous samples, sample adsorption, siphoning, sample evaporation, etc. 

---