Monochromators, systematic

The cubic space group Pm3m (no systematic absences) was chosen for X-ray diffraction studies for reasons previously cited (9). Preliminary crystallographic experiments and subsequent data collection were performed at 2A°C with an automated, four-circle Syntex PI diffractometer, equipped with a graphite monochromator and a pulse-height analyzer. Molybdenum radiation was used for all experiments (Ka, X 0.70930 a K 2 ... 

In 2000, a light beam from a white light source filtered by a monochromator was launched into an optical fiber for transmission absorption spectroscopy by Meriaudeau et al. [65]. The optical fiber carried AuNPs (shape unknown) with a size of 4 nm at its exit end-face (Fig. 10). The end-face of the optical fiber was immersed in a cuvette that could be rinsed with liquids of different refractive index. The LSPR of the AuNPs in air (n = 1) was found at 530 nm and shifted systematically and linearly to higher wavelength with the increase of the refractive index of the AuNP surrounding liquid. They achieved a LSPR shift of about 100 nm for a An of 0.7. The authors described this as a first fiber sensor for refractive indices of solutions. 

Refinement of the individual isotropic parameters of all atoms yields a small negative 5 of Si 1. It is unfeasible that Nd atoms are statistically mixed in the same sites with Si because their volumes are too different ( 27 for Nd versus 1 K for Si). Given the density of the alloy, it is also impossible that all sites except this one are partially occupied. Therefore, the negative 5sii is likely due to the fact that Si atoms have only a fraction of the scattering ability of Nd atoms, and individual displacement parameters of the former cannot be reliably determined from this experiment. Another possible reason is the non-ideality of the selected peak shape function, or other small but unaccounted systematic errors. One of these is an unknown polarization constant of the employed monochromator (see Eq. 2.69). Another possibility is a more complex preferred orientation. As a result, the isotropic displacement parameters of two independent sites occupied by Si were constrained to be identical in a way, the Si atoms were refined in an overall isotropic approximation. 

All sources of error can be divided into systematic and casual. The instrumental polarization (IP) of a telesc ope-polarimeter system is of the first type. It is stipulated, mainly, by that fact that the polarization degree of the light (both reflected and transmitted) varies with incident angle on the optical elements. In astronomical observations such surfaces are the telescopic mirrors, monochromator mirror, diffraction grating, filters, polarizers, SPSP etc. Therefore, even unpolarized light that falls on the main telescope mirror becomes partially elliptically polarized. The contribution of the polarization attributable to the instrument (see [2], for example) is Pj, (pj Qj, Uj and Vj. 

The reason for systematic titration errors is that the equivalence point is indicated too early or too late. This happens when the transition point of the indicator does not exactly match the pH of the equivalence point of the titration (systematic errors caused by wrongly calibrated pipettes or burettes will not be discussed here). The transition point of an indicator gives the experimental endpoint of the titration. Because the term endpoint can also be applied in the sense of theoretical endpoint = equivalence point we shall use here the term transition point to be clear. The same can happen in case of instrumental methods of indication when these methods do not identify the equivalence point correctly, but systematically deviate from it. Color indicators are themselves acid-base systems Hl/1 (HI + H2O 1 + HsO ), the p a value of which is usually denoted as the pA) value, and it normally falls in the range of 2-12. There are bichromic and monochromic indicators. For example, a bichromic indicator may be red as an acid and blue as a base, and a monochromic may be colorless as an acid and violet as a base. In the case of bichromic indicators, the color changes when Chi = cr, that is at the buffer point of the indicator. Of course, the color change does not abruptly occur there, but it is smeared out in an interval (the so-called transition interval of an indicator), roughly in the... 

In most commercial spectrophotometers, the monochromator precedes the sample, illuminating sequentially with single wavelengths. This type of instrument is intended for nonfluorescent materials. A distinct systematic error occurs when a fluorescent sample is introduced as depicted in Fig. 9. 

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