Polarisation studies

Ogundele and White carried out a series of polarisation studies on surgical grade stainless steels in Hanks s physiological solution. Under... 

Figure 19.21 shows the types of crevices used by Wilde " for studying crevice corrosion and pitting of Cr-Ni-Fe alloys in the laboratory and in the field. Types 1 and 5 were used for anodic polarisation studies in nitrogen-saturated 1 mol dm NaCl and in aerated 3-5 mass% NaCl, respectively, and it can be seen that attachment to the conducting lead is by means of a Stern-Makrides pressure gasket Types 3 and 4 were used for field tests... 

Refractive index studies allow measurements of the birefringence, but also of the polarisability. The mean polarisability (a) can be determined using an isotropic liquid solution, whereas the polarisability anisotropy (Aa) is measured in the mesophase. Polarisability studies have been made on palladium, platinum, iridium and silver metallomesogens, and show a higher polarisability for the metal complexes than for their parent ligands. ... 

The analysis may seem rudimentary but for many years it formed the basis of vibrational spectroseopy. With additional information from isotopic substitution and polarisation studies it provides a successfiil means of analysis. For complex systems such as biomolecules this type of analysis is still used. The method offers a simple, useful check on the spectra recorded. It is also needed when the unexpected happens and the observed spectrum does not match expectations it provides clues for further investigation. 

Fluorescence polarisation studies on acenaphthylene labelled polyacrylic acid has demonstrated complexation occurs with polyethylene oxide to give a tightly packed and sterically restricted conformation SS. Neutralisation of the acidic groups restored the polarisation of the fluorescence and together with time resolved fluorescence analysis indicated that the motion of the probe is anisotropic. Solvent partitioning has been observed between glycol methacrylate copolymers from the fluorescence anisotropy changes of... 

A very useful technique which has recently been developed for Fe work, although its application is more general, is the use of polarised radiation. It is convenient to discuss the subject here, but the reader is advised to refer to the appropriate sections in later chapters for more detailed discussion of the spectra of some of the materials mentioned. Polarisation of the emitted y-ray was first shown in 1960 [36], and can take place by the Stark and Zeeman effects already familiar in optical polarisation studies [37]. 

Thus, the time-resolved measurement of such membrane probes contains information on the dynamics of the hindered probe rotation, often interpreted as the micro-viscosity, and about the hindrance of this rotation, usually interpreted as the static packing arrangement of the lipids or the so-called membrane order [136, 137]. Fluorescence polarisation studies in membranes, however, exhibit some major limitations the experimentally determined steady-state and time-re-solved anisotropies characterize the motional restrictions of the reporter molecule itself and give therefore only indirect information about the dye environment, with the consequence that, if the probe is bound covalently to the lipid (TMA-DPH), this attachment may dominate the recorded depolarisation behaviour. The membrane order parameters obtained from freely mobile probes like (DPH) result from a broad distribution of localisation within the hydrophobic interior, the detailed characterisation of which reveals inherent ambiguities [138]. 

F. Krok, J. R. Dygas, B. Misztal-Faraj, Z. Florjaczyk, and W. Bzducha [1999] Impedance and Polarisation Studies of New Lithium Polyelectrolyte Gels,... 

The need for caution in the interpretation of polarisation studies is indicated by the recent work of Fraser and Price [59]. They point out that the transition moment of the carbonyl stretching mode responsible for the amide I absorption will be displaced from the CO direction due to interaction with the C—N vibration, and to an orbital following effect. They have calculated the dichroism of an oriented polypeptide in which the chains have the configuration of Pauling and Corey [60] with a 3.7 residue helix, and have shown that if allowance is made for a displacement of the CO transition moment by 20° towards the NO, the dichroic value obtained is very close to that observed experimentally [54]. The objection to the 3.7 helix based on polarisation studies [61] cannot therefore be maintained. 

Polarisation studies are common in fluorescence spectroscopy. In the more expensive instruments internal polarisers may be automatically switched between horizontal and vertical alignments, otherwise polarisers placed in the sample compartment require manual switching. Plastic polarisers are relatively inexpensive but will absorb and be bleached by hght below about 300 nm and so are unsuitable for UV work. 

Dynamic nuclear polarisation study of (CH3)3CN(0-)C(CH3)3 CHCl3 complex. 

Obuekwe et al. in a series of papers on IRB (Pseudomonas sp.) reported corrosion effects of the bacteria under the micro aerobic (which contains trace amounts of oxygen) conditions [31, 58, 64]. These works included polarisation studies of mild steel in media with and without yeast extract. Those researchers reported that the IRB may contribute to corrosion of mild steel by anodic depolarisation due to their ability to reduce and remove the protective film of ferric compounds. 

However, most pits will stop after a few days. Polarisation studies have demonstrated that when pits stop growing, they will be repassivated. When the metal is polarised once again, these passivated pits will not be reinitiated again, but pitting will start on fresh sites. 

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