Difficult to Understand

Multiple regression procedures are very easily accomplished using software packages such as MiniTab. However, in much of applied research, they can become less useful for several reasons more difficult to understand, cost-benefit ratio is often low, and often underlie a poorly thought-out experiment. 

As the variable numbers increase, so does the complexity of the statistical model and its comprehension. If comprehension becomes more difficult, interpretation becomes nebulous. For example, if researchers have a four- or five-variable model, visualizing what a fourth or fifth dimensimi represents is impossible. If the researchers work in industry, no doubt their job will soon be in jeopardy for nonproductivity. The question is not whether the models fit the data better by an or F test fit, but rather, can the investigators truly comprehend the model s meaning and explain that to others in unequivocal terms In this author s view, it is far better to use a weaker model (lower or 

F value) and understand the relationship between fewer variables than to hide behind a complex model that is applicable only to a specific data set and is not robust enough to hold up to other data collected under similar circumstances. 

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At one time, computational chemistry techniques were used only by experts extremely experienced in using tools that were for the most part difficult to understand and apply. Today, advances in software have produced programs that are easily used by any chemist. Along with new software comes new literature on the subject. There are now books that describe the fundamental principles of computational chemistry at almost any level of detail. A number of books also exist that explain how to apply computational chemistry techniques to simple calculations appropriate for student assignments. There are, in addition, many detailed research papers on advanced topics that are intended to be read only by professional theorists. 

Bromination of 2-dialkylaminothiazoles has been reported to be successful by one author (415) and to fail by others (375. 385). If the mechanism of direct electrophilic substitution is accepted for these compounds, it is difficult to understand why alkyl substitution on such a remote position as exocyclic nitrogen may inhibit this reaction in the C-5 position. 

Coercivity of Thin-Film Media. The coercivity ia a magnetic material is an important parameter for appHcations but it is difficult to understand its physical background. It can be varied from nearly zero to more than 2000 kA/m ia a variety of materials. For thin-film recording media, values of more than 250 kA / m have been reported. First of all the coercivity is an extrinsic parameter and is strongly iafluenced by the microstmctural properties of the layer such as crystal size and shape, composition, and texture. These properties are directly related to the preparation conditions. Material choice and chemical inborn ogeneties are responsible for the Af of a material and this is also an influencing parameter of the final In crystalline material, the crystalline anisotropy field plays an important role. It is difficult to discriminate between all these parameters and to understand the coercivity origin ia the different thin-film materials ia detail. 

Inscrutability The inherent nature of QRA makes the results difficult to understand and use. 

Several steps can be taken to maximize the run time for the reciprocating compressor. Since wear is a function of rubbing speed, the piston speed can be kept to a minimum. Chapter 3 made recommendations for piston speed. Reliability problems due to valves are reputed to account tor 40% of the maintenance cost of the compressor. Valves are the single largest cause for unplanned shutdowns. Basically, valve life can he increased by keeping the speed of the compressor as low as practical. At 360 rpm, the valves are operated six times a second. At 1,200 rpm, ihc valves operate 20 times a second or 1,728,000 times in a day. It is not difficult to understand why the valves are considered critical. To keep the reliability in mind, valve type, material selection and application considerations such as volume ratio, gas corrosiveness, and gas cleanliness need attention by the experts. One final note is that while lubrication is an asset to the rubbing parts, it is not necessarily good for valve reliability. 

London [11] was the first to describe dispersion forces, which were originally termed London s dispersion forces. Subsequently, London s name has been eschewed and replaced by the simpler term dispersion forces. Dispersion forces ensue from charge fluctuations that occur throughout a molecule that arise from electron/nuclei vibrations. They are random in nature and are basically a statistical effect and, because of this, a little difficult to understand. Some years ago Glasstone [12] proffered a simple description of dispersion forces that is as informative now as it was then. He proposed that,... 

The second two-electron integral is a little more difficult to understand formally, it represents the mutual potential energy of the overlap charge distribution -eiAff(r]) s(ri) due to electron 1 with an identical density -eifRi 2) l s0 2) due to electron 2. 

On both experimental and theoretical grounds there is little doubt of the importance of polarizability as a major factor in determining the commonly encountered, though variable, high RS /RO ratios. Were thermodynamic carbon affinities mainly responsible for the usual reactivity order RS > RO, the peculiar behavior of chloroquinolines would be very difficult to understand. There is some indication, however, that carbon affinities roughly parallel basicities (hydrogen affinities), In the latter case, lower RS /RO ratios could be explained in terms of the intermediate complex mechanism, ... 

The failure of 2,5-dimethylpyrrole to dimerize is simple to understand. It is, however, difficult to understand why 2,4- and 3,4-di-methylpyrrole do not form simple dimers. ... 

Treibs and Kolm have reported that, in the complete absence of oxygen and in the dark, pyrrole dissolves in 1.05 equivalents of 0.75 lY aqueous HCl—the clear solution is stable for several hours at room temperature and on basification gives unchanged pyrrole in high yield. (This was difficult to achieve, for the authors state that only two out of four experiments succeeded.) It is very difficult to understand how pyrrole, with an extremely low pKa of the order of zero, can dissolve in 1 equivalent of dilute aqueous acid (1.4 gm pyrrole in 32 ml of aqueous acid). Treibs concludes that protonated pyrrole is stable in solution, and that it is extremely susceptible to autoxida-... 

Despite its attractions for reducing common-pool losses, use of unitization has been more limited than one would expect. Joe Bain (1947, p. 29) noted It is difficult to understand why in the United States, even admitting all obstacles of law and tradition, not more than a dozen pools are 100 percent unitized (out of some 3,000) and only 185 have even partial unitization. Similarly, in 1985 Wiggins and Libccap reported that as late as 1975, only 38 percent of Oklahoma production and 20 percent of Texas production came from field-wide units. 

It is not very difficult to appreciate that if polymer molecules are aligned as in Fig. 18.10 then a much higher tensile strength will be obtained if a test is carried out in the X-X direction as opposed to the Y-Y direction. It is also not difficult to understand why such a material has a lower impact strength than a randomly coiled mass of molecules (Fig. 18.10) because of the ease of cleavage of the material parallel to the X-X direction. 

While none of the 256 possible radius r = 1 binary valued CA are believed to be capable of universal computation, the rule whose long time behavior has proven to be the most difficult to understand fully is rule R22 ... 

We all have an intuitive feel for complexity. An oil painting by Picasso is obviously more complex than the random finger-paint doodles of a three-year-old. The works of Shakespeare are more complex than the rambling prose banged out on a typewriter by the proverbial band of monkeys. Our intuition tells us that complexity is usually greatest in systems whose components are arranged in some intricate difficult-to-understand pattern or, in the case of a dynamical system, when the outcome of some process is difficult to predict from its initial state. 

Similarly, examples of barriers arising largely from simple steric hindrance can be found, as for instance in the hindered diphenyls.35 On the other hand there are many arguments suggesting that this is not the important force in ethane and similar molecules. It would be difficult to understand the relatively slow fall in barrier from ethane to methyl silane to methyl germane on a van der Waals repulsion basis. Furthermore, the small effect of substituting F, Cl, or Br on one end would also seem mysterious. The equilibrium orientation in propylene is opposite to the predictions of one of the quantitative van der Waals theories. Finally, the apparently small effect of bending back the C—H bonds is not in accord with either the electrostatic or van der Waals pictures. 

The discrepancy would be resolved if about 4.8 eV were the actual work function of clean Hg. In this case, however, it would be difficult to understand why 4.50 eV has been consistently measured it is hard to imagine what kind of contamination is responsible for such a highly reproducible situation. On the other hand, if 4.80 eV were the value of for clean Hg, then most of the other metals would show a decrease in work function upon water adsorption less negative than Hg, which is at variance with the expected chemistry of metal surfaces (see later discussion). 

As mentioned in the introduction, before an adequate theory was developed, it was difficult to understand the experimentally determined pho-toinduced PMC signals, especially the minority carrier accumulation near the onset of photocurrents.The reason was that neither conventional solid-state semiconductor theory nor photoelectrochemical theory had taken such a phenomenon into account. But we have shown that it is real and microwave (photo)electrochemical experiments clearly confirm it. 

Not only does the theoretical approach make chemistry more difficult to understand, it also transforms it into a plugging of numbers into inaccurate formula for students to get answers to questions while understanding neither the question nor the answer. 

Because PTFE has low adhesion, high lubricity, and low friction coefficient [14], it is not difficult to understand PTFE film has a lower friction coefficient factor and higher wear rate than PTFE/Si3N4 multilayers under the current experi-... 

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