PAS Technique

Most of the accepted Schiff formulae give equally good results, but we prefer the Schiff reagent of Barger and de Lamater (1948), which gives a brilliant reaction. 

1 g of basic fuchsin is dissolved in 400 ml of distilled water, using heat if necessary. 

Add 1 ml of thionyl chloride (SOCy, stopper the flask and, after shaking, allow to stand for 12 hours. 

Add 2g activated charcoal, shake, and immediately filter. This will keep several months in a well-stoppered dark bottle in the refrigerator. 

Oxidize for 10 minutes in freshly prepared 1% aqueous periodic acid. 

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Initial Pa/ U levels are more difficult to assess, primarily because there is no long-lived or stable isotope of protactinium that can be used as an index isotope. Edwards et al. (1997) analyzed a set of surface coral sub-samples younger than 1000 years by both °Th and Pa techniques. For all samples, Th concentrations were less than 100 p g so that initial °Th/ U values were negligible. Each sub-sample yielded °Th and a ages identical within analytical errors (Fig. 8), indicating that initial Pa/ U was negligible. This suggests that surface corals with typical Th values do not require corrections for initial Pa. Whether or not corals with elevated Th require such corrections is an open question. 

Infrared microscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and photoacoustic spectroscopy (PAS) techniques may be suitable for some types of sample but the use of... 

An alternative technique is the so-called Photothermal Beam Deflection Spectroscopy [PBDS], based on the so-called mirage effect first reported by Boccarra and coworkers [39, 40]. In this case, the periodic temperature rise caused by the absorption of the modulated IR radiation (i.e. the photothermal effect) is detected optically because it causes periodic deflections of a laser beam passing close to the surface of the solid sample. The PBDS technique has some advantages over the PAS technique, because of its lower Hmits of sample dimensions, but it has disadvantages because of the critical geometric setup. Like PAS, PBDS can have advantages with respect to traditional IR technique for the detection of surface... 

PAS techniques require samples to be placed in a spectrophone for analysis. PTS methods allow constant free on-stream inspection at a distance. Particle size may be inferred from the signal level. Since specific surface increases with decreasing size the signals also decrease. A discussion of these techniques has been presented by Kanstad and Nordal [337]. 

Combined Pa and Th dating of corals provides perhaps the most rigorous test for closed-system behavior. Because mass spectrometric Pa techniques are still fairly new and since the measurements themselves are not easy, there is still limited data of this sort. In coming years, Pa measurements will play a major role in assessing the accuracy of Th-based chronologies. The few such data sets on reef-building corals include data reported by Edwards et al. (1997), Gallup et al. (2002), Cutler et al. (2003), and Koetsier et al. (1999). 

FTIR can be used in combination with the PAS technique for in situ measurements. The presence of helium might be necessary to prevent high background noise, which is mainly produced by the silica-based layer. 

Comparison of the PAS technique with the diffuse reflectance spectroscopy (DRS) technique has been discussed [7,32]. 

For the investigation of the kinetics and thermodynamics of intermediate phases of rare earth oxides and photochemical reactions of the surface of rare earth oxides [52], it is reported that photoacoustic spectroscopy (PAS) technique is effective enough. Some information on the lattice structure of powder grains can be attained from the spectra. Raman and resonance Raman spectroscopy were also investigated on rare earth oxides of EU2O3, Dy203, and Tm203 [53]. 

Positron annihilation lifetime spectroscopy (PALS) can be used to measure the free volume in various materials. Jean et al. discussed the application of positron annihilation spectroscopy (PAS) in the detailed study of polymers and polymers with fillers. The primary experimental PAS technique used in this research is PALS, one of the three techniques in the PAS family and a powerful tool for measuring the free volume in various materials. The free volume has a great role in polymer research and is widely used to explain the behaviour of physical properties such as glass transition temperature, viscosity and physical ageing. Free volume is affected by the blending of polymers, ageing and addition... 

PA techniques can therefore be used to assess the amount of damage in a material, if that damage gives rise to vacancies or other positron trap sites. 

The initial step of the PAT/KOH/PAS reaction generates aldehydes from the Q, C7, and C9 classes of sialic acids and from tissue diols unassociated with sialic acid residues. Such aldehydes are stained blue with a Schiff reagent prepared from the phenothiazine dye, thionine. The subsequent saponification step removes acetyl groups from the Q class of sialic acids which are then stained red by the standard PAS procedure. Sites containing mixtures of these components stain in various shades of purple. As will be seen in Fig. 4, tissue sites which stain blue in the PAT/KOH/PAS procedure and red (positive) with the PBT/KOH/PAS technique are considered to contain the C7 class of sialit acids we have identified a predominance of such acids in a small number of tumours (Culling et al. 1977 a). 

These results confirm that the local environment of the Fe atoms in the bee lattice of RPV steels as well as the creation of new defects that are observable by PAS techniques almost stabilises after some initial changes. On the other hand, longterm thermal treatment (at about 290 °C) can cause some defect re-annealing, and acts in the opposite manner to radiation-induced defects. 

In the future, the application of PAS techniques to the development of new types of steels with well-defined parameters (materials for fusion reactors, etc.) or to evaluations of the effectiveness of post-radiation heat treatments can be foreseen. The utilisation of a high-precision positron microscope in RPV steel investigations would surely be a good example [156],... 

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