Classics Illustrated

The occurrence of nonradiative losses is classically illustrated in Figure 3. At sufficiently high temperature the emitting state relaxes to the ground state by the crossover at B of the two curves. In fact, for many broad-band emitting phosphors the temperature dependence of the nonradiative decay rate P is given bv equation 1 ... 

Substitution of one ligand by another can generate, or alter, spin crossover characteristics. The systems studied early provide the classic illustration of this effect. Thus [Fe(py)4(NCS)2] is high spin at room temperature and does not undergo a thermal spin transition. Substitution of two of the pyridine molecules by a phenanthroline molecule gives [Fe (phen)(py)2 (NCS)2] which does undergo a thermal transition [99, 141], as does the species in which the remaining two pyridines are substituted [Fe(phen)2 (NCS)2]. As would be expected, T1/2 for the former complex (106 K) is lower... 

The enamel of mammalian teeth is much more heavily mineralized than bone, which makes it much harder. In addition, it does not contain collagen, although in its final mature state it does contain small amounts of specialized matrix proteins. Early tooth development is a classical illustration of the interaction between two tissue types (epithelial cells and... 

In some regions of the country, notably the Northwest and now in the Southeast, lumbering is a major factor in the economy. The Northwest is a classic illustration of the economic importance of lumbering. The decline in demand for timber products, due to the economy, resulted in a loss of thousands of jobs in the Pacific Northwest. The fifteen to twenty billion dollar a year industry has been almost at a standstill. 

Classic illustrations of this approach are found in Hobsbawm and Rude (1968) and Tilly (1978). 

Such ordering optimizes the Mudclung energy. The classic illustration of this effect is found in the spinel Fe3+[Fc2+Fc3+]04. Ordering of the B-site Fe2+ and Fe3+ ions into alternate (001) B-site layers below 119°K distorts the crystal to orthorhombic symmetry (248,637,639). 

A study led by NIMH s Alan Zametkin et al. (1990) received a great deal of publicity for finding increased brain metabolism in PET scans of adults with a history of ADHD in childhood. However, when the sexes were compared separately, there was no statistically significant difference between the controls and ADHD adults. To achieve significance, the data were lumped together to include a disproportionate number of women in the controls. In addition, when individual areas of the brain were compared between controls and ADHD adults, no differences were found. It is usually possible to massage data to produce some sort of statistical result, and Zametkin et al. s study is a classic illustration. 

In Chapter 10 we discussed conjugate addition to unsaturated carbonyl compounds in contrast to direct addition to the carbonyl group. A classic illustration is the addition of HCN to butenone. Two products can be formed. 

Four-membered peroxides are an interesting group of compounds, and will be discussed briefly. Such compounds have the ability to yield excited state carbonyl fragments upon thermolysis 154 in such cases, chemiluminesence is often observed. A classic illustration of this type of chemistry is the reaction of hydrogen peroxide with oxalyl derivatives, for example, when the 2,4-dinitro-... 

It is well known [89] that, in solution state 13C NMR, the 13C chemical shift for C=0 carbons is shifted to a higher value by hydrogen bonding. In general, this is also observed for the isotropic 13C chemical shift in solid state 13C NMR. A classic illustration is a-diacetamide, the crystal structure [90] of which contains dimers, with only one of the two carbonyl groups involved in hydrogen bonding ... 

Type 2 is ductile crack propagation with the crack opening to form a V-notch. Finally, the crack becomes catastrophic. It is found in nylon and other melt-spun synthetics. Classical illustrations of this type are readily available (3, 4). However, variations can occur. Figures la and lb show a polyester fiber subjected to tensile stress in which, after the V-notch formed, failure continued along a plane parallel to the fiber axis before eventually crossing the fiber. Thus, a split-level transverse break had occurred. 

A classic illustration of scaffold decoration is the trisubstituted 1,3,5-triazine. The starting material trichloro-l,3,5-triazine is inexpensive, and the halogens can be displaced by nucleophilic aromatic substitutions one by one. Such chemistry was well precedented in pre-combinatorial days, and used on a large scale for the synthesis of colour-fast reactive dyes. The overall reaction sequence has an appeal in its simplicity, and both academic and industrial practitioners have reported a steady trickle of such triazine-based libraries over the last 20 years. Novelty will come either from the particular set of nucleophiles employed or the assay targets. 

The Friedel-Crafts alkylation is a classic illustration of the general class of electrophilic aromatic substitutions. Traditionally, Friedel-Crafts reactions require an alkyl halide as the electrophile source and at least a molar equivalent of aluminum chloride, a hygroscopic and caustic powder that is rather problematic to use in the introductory lab. An easy variant of this procedure utilizes the reactive substrate 1,4-dimethoxybenzene, /er butyl alcohol as the electrophile precursor, and sulfuric acid as the catalyst (72). We run this reaction on a microscale, and use commercial rubbing alcohol (70% aqueous 2-propanol) in place of methanol as the recystallization solvent. The product, l,4-di-7er/-butyl-2,5-dimethoxybenzene, exhibits simple and NMR, and... 

Eastman Chemical, regarded as a classic illustration of the process intensificationThe reaction was traditionally carried out using the processing scheme shown in Fig. 2(A), which consists of one reactor and a train of nine distillation columns. In the RD implementation, only one column is required and nearly 100% conversion is achieved with significantly reduced capital and operating costs (Fig. 2B). 

The Long Island case is a classic illustration of many of the factors known to enhance the development of resistance, including intensive commercial production of the insect s principal hosts (potato, tomato, eggplant), a very small number of wild hosts (Solanum rostratum, S. dulcamara) offering only minimal opportunities for avoidance of selection on untreated refugia, and a relatively isolated island location. 

The classic illustration of how the valency of an ion can be determined from e m f measurements is that of the mercurous 10ns [Hg2++] investigated by Ogg (Zeitsch fhysik Chem, 27. 285, 1898)... 

Figure 22.1 Graphical illustration of the data from Table 22.1. To illustrate accuracy and precision the standard deviations have been calculated using formula 22.8. Note the differences between the arithmetic means indicated on the graph by a short vertical bar and the corresponding median values, which are arrowed. For the results from chemists 3 and 4, the difference is fairly large. Chemist 1 has committed very probably a systematic error. On the right, a classic illustration of the precision and accuracy depicted with the aid of a target. This image is less simple than it would appear because there remains an uncertainty in both x and y.

A classic illustration of psychic ability gone wild is the renowned healer Edgar Cayce, who worked as a psychic diagnostician (his term) by entering a trance and suggesting cures for clients he had never even met. 

A classic illustration of the quality of a calculation is provided considering the effect of the basis set of say, a Hartree-Fock (HF) calculation. (See Sect. 3 for further discussion of the HF method). For MO schemes like HF theory, the variational principle states that the lower the computed total energy, the better the result [1]. The energy can be lowered by increasing the basis set size and so large basis set calculations are often described as good quality. However, this need not imply that experiment is also well reproduced. If the basic assumptions of the HF approximation are inappropriate, then it may not be possible to predict experimental data reliably, irrespective of the basis set size. As will be seen later, this is often the case for HF calculations on TM systems. 

A classic illustration of the quaternary structure and its effect on protein properties is a comparison of hemoglobin, an allosteric protein, with myoglobin, which consists of a single polypeptide chain. 

Block valves on lines feeding the column should be located so that the piping sections upstream of the valve drain back to the upstream unit. The incident described in Fig. 13.2 is a classic illustration of the importance of this rule. 

The classic illustration of the central limit theorem comes from throwing dice. The probability that we observe a certain niunber of points throwing a single die is shown in Fig. 2.6(a). The possible outcomes are the integers from 1 to 6, and if the die is not biased all of them have the same chance to occur, leading to a distribution that is far from normal. 

FIGURE 32.6 Dispersion as a function of wavelength for a number of ceramics. The inset is the classic illustration of dispersion, a prism separating white light into its spectral components. 

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