Dispersion artefact

This resonant Mie scattering effect is the cause of the phenomenon previously referred to as the dispersion artefact , which was an inaccurate description because the effect was not solely due to dispersion and it is not an artefact because it can be explained fully. With an understanding of the physics behind resonant Mie scattering, preliminary algorithms based on the extended multiplicative signal correction (EMSC) have been developed. The EMSC... 

Bassan, P. et al (2009) Reflection contributions to the dispersion artefact in FTIR spectra of single biological cells. Analyst, 134, 1171-1175. 

Some historians date the Iron Age to around 1200 bc, when the Hittite empire was destroyed and its smiths were dispersed, spreading the knowledge of ironworking. But man-made iron artefacts existed before 2500 bc. The Iron Age, along with the earlier Bronze and Stone Ages, is an invention of nineteenth-century archaeologists and of questionable value today. 

For all these reasons diffraction gratings are used in most dispersive optical instruments. It is however essential to bear in mind the artefacts that can arise from harmonic transmissions. 

Other analytical methods can also be applied for the detection of F in archaeological artefacts, especially when it is possible to take a sample or to perform microdestructive analysis. These are namely the electron microprobe with a wavelength-dispersive detector (WDX), secondary ion mass spectrometry (SIMS), X-ray fluorescence analysis under vacuum (XRF), transmission electron or scanning electron microscopy coupled with an energy-dispersive detector equipped with an ultrathin window (TEM/SEM-EDX). Fluorine can also be measured by means of classical potentiometry using an ion-selective electrode or ion chromatography. 

Further work in the energy-dispersive CSCT area is needed to determine the limits to performance set by photon noise and reconstruction artefacts. Comparison of the plastic profiles of Fig. 20 with the diffraction profile of TNT (Fig. 5) derived from a direct tomographic energy-dispersive XDI device shown in Fig. 4 suggests that the latter has currently an advantage owing to its avoidance of reconstruction artefacts. 

Artefacts that arise from gas in the stomach and adjacent bowel often limit the diagnostic accuracy of abdominal ultrasound. Research to overcome this problem has focused on cellulose-based suspensions. An agent has been developed based on simethicone-coated cellulose— SonoRx (Bracco Diagnostics, Princeton, NJ), which displaces and disperses gas bubbles. In a phase 2 chnical study, 93 patients underwent upper abdominal sonography before and after a randomized dose of the contrast agent (200, 400, 600, 800, or 1000 ml) (15). Anatomical visualization was improved as follows the stomach in 82% of patients, the duodenum in 63%, the pancreatic head and body in 61%, and the pancreatic tail in 67%. There were 14 adverse events in 11 patients and only five were considered to be related to the contrast agent. The main adverse effects were mild diarrhea and nausea. 

In 1989, experimental dc-SHG data for Ne [70] suggested that at low frequencies y( decreased with increase in m2 (or l2) - so-called anomalous dispersion - that is to say A in Eq. (62) must be negative. Later, it turned out that this was an experimental artefact [71] ab initio calculations [72,73] had already questioned the observation. However, before that happened, I was able to use Eqs. (18) and (62) and, in a very simple way [74], show that indeed A could not be negative (or, at least, not to the extent suggested). It is only the second part of Eq. (18) which can be negative and, in terms of the standard sum rules S.k.t and an expansion in l2, I found this term contributes to A the amount... 

Moreover, the presence of an artefact in the analytical path for analyte separation/concentration is not included in the definition of X. Also, the sample, reagent and carrier solutions are considered as a whole, so that differences in the diffusion coefficients of the different chemical species are not considered. The occurrence of chemical reactions altering the sample dispersion [113] is not considered. 

Nowadays, there is a satisfactory description of physical dispersion in single-channel flow injection systems in which artefacts do not play a pronounced role in the process. Numerous attempts have been made to extend the model to situations involving chemical reactions. In general, the strategy is to consider modifications to the concentrations of the reactant species and Dm. These parameters refer initially only to the main reactants but, as the chemical reactions proceed, Dm of the formed products (and their instant concentrations) should be also taken into account [55]. For a complete description of flow systems comprising several confluent streams, Eqs. 3.4 and 3.10—3.12 should be combined. 

The presence of artefacts in the analytical path, such as mixing chambers, tubing connections, de-bubblers and other chamber-like components, can also affect sample dispersion in flow injection analysis. The effects of a mixing chamber and the detector inner volume are discussed in 3.1.2.2 and 6.3.2, respectively. The presence of devices for liquid—liquid extraction and gas diffusion (or dialysis) alters dispersion, and is dealt with in Chapter 8. 

In 1977 Krishnamurthy and Subramanian published an exact theoretical analysis of FFF [19], based on their generalized dispersion theory. Without touching on the details of a complicated mathematical treatment, with the aid of which they solved the problems of both the separation and dispersion processes that occur in the FFF channel during the complete separation from the injection to the elution, let us only say in general that their solution makes it possible to explain some experimental artefacts in detail. These artefacts could not be explained by means of the non-equilibrium theory of FFF mentioned above, which is based on some asymptotic assumptions. Perhaps the most important discrepancy between the theory and the experimental data is that the zone spreading that is observed is considerably larger than the spreading predicted by the theory. 

Napper (1980b). For example, Scheutjens and Fleer claim that at low concentrations of polymer the interaction between particles dispersed in a polymer solution is attractive at all separations. Only at high volume fractions does very strong repulsion appear at distances comparaUe to the rms end-to-end distance of the macromolecule. The physical b is for such a qualitative change in the sign of the free energy of interaction at larger separations seems dilRcult to understand. Perhaps it is an artefact of the procedures adopted. 

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