Fundamental weaknesses

Further, it has been shown that the mathematical formulation of Kumar s model, including the condition of detachment, cord not adequately describe the experimental situation—Kumar s model has several fundamental weaknesses, the computational simplicity being achieved at the expense of physical reahty. 

Solubility and kinetics methods for distinguishing adsorption from surface precipitation suffer from the fundamental weakness of being macroscopic approaches that do not involve a direct examination of the solid phase. Information about the composition of an aqueous solution phase is not sufficient to permit a clear inference of a sorption mechanism because the aqueous solution phase does not determine uniquely the nature of its contiguous solid phases, even at equilibrium (49). Perhaps more important is the fact that adsorption and surface precipitation are essentially molecular concepts on which strictly macroscopic approaches can provide no unambiguous data (12, 21). Molecular concepts can be studied only by molecular methods. 

In summary, assumptions (1) and (2) are unnecessary and have been avoided in more advanced models. Assumptions (3) and (4) are unavoidable and illustrate the fundamental weakness of most enzymatic sensors, particularly those depending on detection of pH changes. Assumptions (5) and (6) can be avoided to some extent by experimental design, but should be always accounted for in the model. Assumption (7) is easily avoidable. There is another assumption that has not been mentioned, the equality of concentration and activity. As discussed in Chapter 1, that cannot always be a justifiable assumption. 

Despite the success in parameterizing acid/base and many other properties for a range of different compounds, it is obvious that the simple electrostatic model used by Taft and extended by others [27, 28] have fundamental weaknesses - both with regards to the domain of validity and at a more fundamental level. The model is more intuitive than physical, in the sense that the inductive effect, polarisation effect, resonance effect, mesomeric effect and steric effect have no proper quantum mechanical definition, and can therefore not be derived directly from the system s wave function [29,30]. 

Despite the fundamental weakness of the effective diffusivity approach to multicomponent diffusion, it has been widely used in the past and so it would seem to be worthwhile to spend some time to delineate the conditions when such an approach is justified. Useful limiting cases of the exact relation (Eq. 6.1.7) include... 

Although this route has the same fundamental weakness of being coupled to another product (adiponitrile), the future of nylon 6,6 and the route to its... 

To gain some experience in the evaluation of perturbation contributions to j and Ej and to motivate an analysis of a fundamental weakness of the Buillouin-Wigner perturbation theory (BWPT), let us now consider a few examples. First, we evaluate the first-order correction to the energy that arises from the n = 0 term in Eq. (3.11) ... 

The fundamental weakness of this ligand-based approach, the disregard of any enzyme specihc interactions, may also be viewed as a strength Metabolism is not restricted to oxidation mediated by cytochrome, nor is it restricted to electrophilic attack. Fukui functions lf as well as/ ) may thus help to imderstand in vivo metabolic reactions of unknown enzymatic origin. 

The compositional and performance features of the zinc oxide-eugenol and zinc oxide-ort/zo-ethoxybenzoic acid cements were dealt with in Sections II.B.3 and II.B.4. While employed for temporary luting and filling, the ZOE materials find their major use in cavity lining. The fundamentally weak cement materials are usually reinforced for this... 

During the 1980s and 1990s, Corey published results from his efforts to overcome the fundamentally weak point of the synthesis, the lack of stereocontrol. This explicitly concerns attempts to find stereoselective conditions for the Diels-Alder reaction and the reduction of the keto-fimction. Both areas of the work subsequently gained general importance. 

Because of its simplicity and wide utility, the Langmuir isotherm has found wide applicability in a number of useful situations. Like many such classic approaches, it has its fundamental weaknesses, but its utility generally outweighs its shortcomings. The Langmuir isotherm model is based on the assumptions that adsorption is restricted to monolayer coverage, that adsorption is localized (i.e., that specific adsorption sites exist and interactions are between the site and a specific molecule), and that the heat of adsorption is independent of the amount of material adsorbed. The Langmuir approach is based on a molecular kinetic model of the adsorption-desorption process in which the rate of adsorption (rate constant /ca) is assumed to be proportional to the partial pressure of the adsorbate (p) and the number of unoccupied adsorption sites (N - n), where N is the total number of adsorption sites on the surface and n is the number of occupied sites, and the rate of desorption (rate constant d) is proportional to n. 

Each of these structures has the same fundamental weakness it implies that the central sulfur atom somehow interacts more strongly with one oxygen atom than with the other. The explanation for this contradiction is that the structure of the molecule cannot be accurately represented by a single Lewis strucmre. Instead we say that the real strucmre corresponds to an average of all the valid Lewis strucmres, and we call this average a resonance hybrid of the contributing Lewis strucmres. It is very important to emphasize that the double-headed arrow does not mean that the structure alternates between the two possibilities it indicates that the two structures shown for SO2 are resonance structures, contributing to a resonance hybrid. In resonance structures, the positions of all atoms are identical only the positions of the electrons are different. 

However, while there are many examples that have addressed clinically important adverse reactions, systematic reviews have a fundamental weakness in their absolute reliance on the availability and quality of primary data. The lack of research activity in several areas of drug safety (as illustrated in Table 1) limits the scope of systematic reviews and hinders the development of comprehensive assessments of specific adverse reactions in a technique described as teleoanalysis [6], which is an exploration that sues data from all available sources, including randomized trials, observational studies, and even case series and case reports. 

For made-in items, the equivalent is economic batch quantity (EBQ). However, lack of communication with other parts of the chain, and negligible effort to understand changing conditions, constitute fundamental weaknesses. 

This should be borne in mind when making, or interpreting, comparisons of accident data since it is a fundamental weakness of such comparisons. In general, a comparison will be valid only to the extent that the risk levels in the organisations being compared are equal. 

The fundamental weaknesses of plastics are caused by their macromolecular structure and relativeiy weak bonding forces. Piastics are thus subject to decidedly greater influences by the effects of heat, light, and oxygen, etc. than are metals or mineral materials. These and additional external influences, such as chemicals and radiation, initiate chemicai aging processes that cause the deterioration of properties and thus shorten the life span of piastic parts. 

Another fundamental weakness of block copolymer lithography is the inability to fabricate not only various geometries, but also geometries of multiple sizes and pitches within one resist layer. One possible solution may lie in block copolymers that can be crosslinked through the use of blended photoactive compounds, such as work shown by the Ober group on PaMS-h-PHOST (Bosworth et al., 2008). While it has already been shown that solvent... 

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