Artifacts, chemical

As already mentioned, this operative definition is one of the most popular, and I must confess that I have never understood why. First of all, the notion of Darwiiuan evolution can only be applied to a population - therefore immediately excluding all single specimens, artifacts, chemical, and artificial fife forms. Suppose that some NASA astronauts encountered single plants or single dangerous animals they would not define them as alive, since there is no Darwinian population, and they may be eaten up in the meantime. Victims of a wrong defiiution of life ... 

An artifact is an inclusion in some system, made by animals or man. Spider webs, bird nests, beaver dams, houses, books, machines, music, paintings, and language are artifacts. They may or may not be prostheaes, inventions which carry out some critical process essential to a living system. An artificial pacemaker for a human heart is an example of an artifact which can replace a pathological process with a healthy one. Insulin and thyroxine are replacement drugs which are human artifacts. Chemical, mechanical, or electronic artifacts have been constructed which carry out some functions of all levels of living systems. 

An error which is difficult to avoid in the collection method described is the introduction of artifact chemical compounds into the urine during collection which show up in the later chemical analysis. Contamination of the collected urine by hair, feces, drinking water, food scraps, metabolic byproducts of microbial fermentation and air oxidation can be reduced by design of the collection procedure. To reduce chemical and microbial contamination further, urine can be collected under a thin layer of toluene in a reservoir with continuous urine flow into a refrigerated collection jar where it is rapidly frozen. Experience with human urine collection indicated little change in chemical composition of frozen urine after several months storage. 

Benoit, G. Hunter, K. S. Rozan, T. F. Sources of Trace Metal Contamination Artifacts During Collection, Handling, and Analysis of Freshwaters, Anal. Chem. 1997, 69, 1006-1011. Keith, L. H., ed. Principles of Environmental Sampling, American Chemical Society Washington, DC, 1988. 

Structure calculation algorithms in general assume that the experimental list of restraints is completely free of errors. This is usually true only in the final stages of a structure calculation, when all errors (e.g., in the assignment of chemical shifts or NOEs) have been identified, often in a laborious iterative process. Many effects can produce inconsistent or incorrect restraints, e.g., artifact peaks, imprecise peak positions, and insufficient error bounds to correct for spin diffusion. 

For thin-film samples, abrupt changes in refractive indices at interfrees give rise to several complicated multiple reflection effects. Baselines become distorted into complex, sinusoidal, fringing patterns, and the intensities of absorption bands can be distorted by multiple reflections of the probe beam. These artifacts are difficult to model realistically and at present are probably the greatest limiters for quantitative work in thin films. Note, however, that these interferences are functions of the complex refractive index, thickness, and morphology of the layers. Thus, properly analyzed, useful information beyond that of chemical bonding potentially may be extracted from the FTIR speara. 

Earlier analyses making use of AH vs. AS plots generated many p values in the experimentally accessible range, and at least some of these are probably artifacts resulting from the error correlation in this type of plot. Exner s treatment yields p values that may be positive or negative and that are often experimentally inaccessible. Some authors have associated isokinetic relationships and p values with specific chemical phenomena, particularly solvation effects and solvent structure, but skepticism seems justified in view of the treatments of Exner and Krug et al. At the present time an isokinetic relationship should not be claimed solely on the basis of a plot of AH vs. A5, but should be examined by the Exner or Krug methods. 

Pandya et al. have used extended X-ray ascription fine structure (EXAFS) to study both cathodically deposited -Ni(OH)2 and chemically prepared / -Ni(OH)2 [44], Measurements were done at both 77 and 297 K. The results for / -Ni(OH)2 are in agreement with the neutron diffraction data [22]. In the case of -Ni(OH)2 they found a contraction in the first Ni-Ni bond distance in the basal plane. The value was 3.13A for / -Ni(OH)2 and 3.08A for a-Ni(OH)2. The fact that a similar significant contraction of 0.05A was seen at both 77 and 297K when using two reference compounds (NiO and / -Ni(OH)2) led them to conclude that the contraction was a real effect and not an artifact due to structural disorder. They speculate that the contraction may be due to hydrogen bonding of OH groups in the brucite planes with intercalated water molecules. These ex-situ results on a - Ni(OH)2 were compared with in-situ results in I mol L"1 KOH. In the ex-situ experiments the a - Ni(OH)2 was prepared electrochemi-cally, washed with water and dried in vac-... 

There is indeed some disagreement as to whether values of AC carry chemical meaning. Although many workers5 believe they do, others6 would argue that these small effects are instead more likely the artifacts of an incomplete theoretical model or a chemical path that intrudes to a minor extent near one of the temperature extremes. It seems that the matter cannot be settled in any general way. 

Electrochemical cells play important roles in both the purification and the preservation of metallic materials. Redox reactions are used throughout the chemical industry to extract metals from their ores. However, redox reactions also corrode the artifacts that industry produces. What redox reactions achieve, redox reactions can destroy. 

A diazodiphenoquinone is also produced as a chemical artifact (Knackmuss and Beckmann 1973). There are, however, a nnmber of unresolved features of the degradation, including the mechanisms for production of 2,6-dihydroxypyridine and oxidative fission of the pyridine ring. 

In some cases a principal components analysis of a spectroscopic- chromatographic data-set detects only one significant PC. This indicates that only one chemical species is present and that the chromatographic peak is pure. However, by the presence of noise and artifacts, such as a drifting baseline or a nonlinear response, conclusions on peak purity may be wrong. Because the peak purity assessment is the first step in the detection and identification of an impurity by factor analysis, we give some attention to this subject in this chapter. 

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