Applied artifacts

Artifact removal and/or linearization. A common form of artifact removal is baseline correction of a spectrum or chromatogram. Common linearizations are the conversion of spectral transmittance into spectral absorbance and the multiplicative scatter correction for diffuse reflectance spectra. We must be very careful when attempting to remove artifacts. If we do not remove them correctly, we can actually introduce other artifacts that are worse than the ones we are trying to remove. But, for every artifact that we can correctly remove from the data, we make available additional degrees-of-freedom that the model can use to fit the relationship between the concentrations and the absorbances. This translates into greater precision and robustness of the calibration. Thus, if we can do it properly, it is always better to remove an artifact than to rely on the calibration to fit it. Similar reasoning applies to data linearization. 

Many current multidimensional methods are based on instruments that combine measurements of several luminescence variables and present a multiparameter data set. The challenge of analyzing such complex data has stimulated the application of special mathematical methods (80-85) that are made practical only with the aid of computers. It is to be expected that future analytical strategies will rely heavily on computerized pattern recognition methods (79, 86) applied to libraries of standardized multidimensional spectra, a development that will require that published luminescence spectra be routinely corrected for instrumental artifacts. Warner et al, (84) have discussed the multiparameter nature of luminescence measurements in detail and list fourteen different parameters that can be combined in various combinations for simultaneous measurement, thereby maximizing luminescence selectivity with multidimensional measurements. Table II is adapted from their paper with the inclusion of a few additional parameters. 

A similar concern due to lateral motion also applies to purely qualitative imaging. Sugisaki et al. [38] observed an artifact in their simultaneously topographic and adhesion... 

Avoid having moving metal objects near the magnet when carrying out nOe difference experiments, to prevent random variations in frequency. A small line-broadening ( 2 Hz) can also be applied to the spectra before or after subtraction, to reduce subtraction artifacts. 

Besides the extraterrestrial application of MIMOS, there are a number of terrestrial applications, such as the investigation of rock paintings, ancient artifacts, and enviromnental science, where the instrument has been applied successfully. 

Fig. 5.5.5 1 D CSI datasets showing the extent of conversion during a batch reaction. The form of the feature identified as peak B is associated with a single chemical shift i.e., it is of constant form at all positions across the bed, and therefore shows that the extent of conversion is uniform throughout the bed. The low intensity horizontal streaking" effect observed in these datasets and that shown in Figure 5.5.6 are artifacts arising from the automatic phase correction applied to the data ...

Farquar, R. M. and V. Vitali (1989), Lead isotope measurements and their application to Roman artifacts from Carthage, Museum Applied Science Center for Archaeology Papers in Science and Archaeology, Vol. 6, pp. 39-45. 

Miller, D. S. and G. A. Wagner (1981), Fission track ages applied to obsidian artifacts from South America, Nucl. Tracks 5, 147-155. 

Taking into consideration that antenna xanthophylls not only possess original absorption but also resonance Raman spectra, and the fact that the Raman signal is virtually free from vibrational spectroscopy artifacts (water, sample condition, etc.), it seemed of obvious advantage to apply the described combination of spectroscopies for the identification of these pigments. 

It is important to stress that ATR absorbance is strongly affected by the sample/crystal contact. Quantitative results are thus difficult to obtain even if the contact is maintained during the sample rotation that is required to record all four polarized spectra. A reference band that does not show significant dichroism is thus most often used to normalize the polarized absorbances in order to obtain quantitative data. For instance, the 1,410 cm-1 band of PET has often been chosen for that purpose, not only for ATR studies but also for specular reflectance (see below) and even transmission studies when the sample thickness is not uniform. It was shown that an appropriate normalization is possible even if no such reference band is available, by using a combination of two bands with orthogonal dichroism [34]. When performing ATR experiments, one should also make certain that the applied pressure does not create artifacts by affecting the structure of the sample. 

The MD simulations were carried out under standard temperature and pressure. A 1 fs time step was used with SHAKE25 applied to bonds. A 2 fs time step with SHAKE was used in the d(IC)6 d(IC)6 —> d(GC)6 d(GC)6 calculations. The non-bonded interactions for DNA complexes were subject to 10 -12 A spherical cutoff whereas no cutoff was applied to solute-solute interactions to avoid cutoff artifacts on coulombic interactions between sodium ions with phosphates. In the case of d(IC)6 d(IC)6 —> d(GC)6 d(GC)6 calculations an 8 A spherical cutoff was applied to non-bonded interactions. A weak harmonic restraint of 5.0 kcal/mol was imposed to avoid the disruption of terminal base pairs during FEP simulations of netropsin —> 0 and 2-imidazole-distamycin —> distamycin calculations. 

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