Soret number

Holmium - the atomic number is 67 and the chemical symbol is Ho. The name derives from the Latin holmia for Stockholm . It was discovered in erbia earth by the Swiss chemist J. L. Soret in 1878, who referred to it as element X. It was later independently discovered by the Swedish chemist Per Theodor Cleve in 1879. It was first isolated in 1911 by Holmberg, who proposed the name holmium either to recognize the discoverer Per Cleve, who was from Stockholm or perhaps to establish his own name in history. 

Metalloporphyrins, MP, represent derivatives of porphyrin, P, in which four pyrrole fragments are bound together by methine bridges (Fig. 13). The diversity of porphyrins is due to the possibility of variation for substituents R in the periphery of the porphyrin ring. A typical optical spectrum of a P solution is presented in Fig. 14. One can point out quite a number of characteristic bands in it. The most intensive short-wave peak in the P absorption spectrum (/max 400 nm) corresponds to the transition S0 -+ S2 and is referred to as Soret band. The extinction coefficient of this band is very large, as a rule, and amounts to 10 -106 M 1 cm-1. The less intensive long-wave bands of P absorption correspond to the S0 - Sx transition (bands I-IV in Fig. 14). Complexation with the metal results in a rise of the symmetry of the molecule, due to which MP molecules have only two bands in the long-wave part of the absorption spectra. Most of the metalloporphyrins are characterized by intense luminescence. The time of MP fluorescence decay (transition Si - S0) is short and amounts to 10"8 to 10 9 s. Besides the transition... 

The theory of the Fe(III) heme spectra has been given in the previous article (52) and in particular the difference between the absorption spectra of high-spin and low-spin species has been stressed. The application of this theory to some proteins has also been described in that article but its purpose was mainly to draw attention to normal spectra. Here we shall point to a number of anomalous spectra especially concerning the movement of the Soret band to much shorter wavelengths than 400 nm. There is a simultaneous notable broadening of this band and a fall in its extinction coefficient. Such effects have frequently been seen in simple model systems and so we deal these first. 

Table 14 gives data on the effect of acidification on the Soret band of a number of proteins. Accompanying the drop in the wavelength there is a decrease in intensity of the band. Directly comparable with this observation is the study of hemes incorporated into polymers by Weight-man (66). His results show that the Soret band moves well below 400 nm... 

Fig. 1 Basic structure (left side) and the absorption spectra (right side) of some photosensitizers. The absorption spectra of porphyrins (derived from porphins) consists of a Soret band (around 400 nm) and four Q-bands. Upon reduction of one or two double-bonds of the tetra-pyrrole structure or by expanding the number of 7i-electrons (by expanding the ring structure), the outermost Q-band becomes bathochromically shifted and the absorption coefficient increased as indicated on the figure. As described in the text, such chemical modifications are important for improving the therapeutic effect in deeper tissue layers...

So far, there is a considerable uncertainty about the Soret coefficients in the literature, and there is only one system, namely polystyrene (PS) in toluene, which has been investigated by a substantial number of different authors with different experimental techniques, and for which a reasonable agreement has been achieved [6,11,12,19,21]. 

Figure 6 shows the respective data plotted according to (21) for a number of blends with different degrees of polymerization. The left plot shows the Soret coefficients as measured and the right one after normalization to the mean field static structure factor calculated from the Flory-Huggins model, cf. (7). Although the structure factors and the Soret coefficients of the different samples vary by more... 

Fig. 6 Left Soret coefficient. S j for a number of PDMS/PEMS blends. The red bullets correspond to the critical blend with a critical temperature of Tc = 38.6 °C. Right Same data as left normalized to mean field static structure factor S(0). The legends give the PDMS and PEMS molar masses in kg mor1 [97]...

These equations are called the Navier-Stokes equations, and when supplemented by the state equation for fluid pressure and species transport equations, they form the basis for any computational model describing the flows in fires. For simplicity, several approximations are inherent (see Equation 20.3) (no Soret/Dufour effects, no viscous dissipation, Fickian diffusion, equal diffusion coefficients of all species, unit Lewis number). 

Heme prosthetic groups have strong absorption in visible-Soret spectral regions. This heme absorption is extremely sensitive to the stmcture of porphyrin as well as to the redox and ligand binding states of the iron. Thus, hemes a and as must exhibit differences in their absorption spectra even if their respeetive iron atoms are in the same oxidation state, since the number of ligands bound to heme a is different from the number of ligands bound to heme as. Careful measurements of the absorption spectra and the... 

The equation for conservation of energy will be written under the assumptions that the Mach number is small and that the work done by body forces is negligible, both of which are accurate approximations for the deflagration problems considered. In addition, we shall neglect the Dufour effect (and later the Soret effect), so that by use of equation (1-6) in equation (3-72), in which h = Yj= i we obtain... 

Finally, to facilitate the mathematical developments, it is convenient to assume for the gas phase that the second-order Soret and Dufour diffusion processes are unimportant the heat capacities at constant pressure Cp, and the thermal conductivity coeflBcients fc, are constants the binary diffusion coeflBcients D are equal for all pairs of species and the thermal and mass diflFusion rates are equal such that the Lewis number is unity. 

A widely used practice of suppliers and investigators is to give the so-called RZ (Reinheits Zahl) number which is the ratio (often around 3.0) of the absorbance at 403 nm (Soret band) and 275 nm. This value, however, is not a real measure of purity. In fact. 

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