Side-wall sampling

Figure 1. Sampling devices A, L-shaped probe B, straight probes C, side-wall sampling and D, side-wall sampling with a projection. (Reproduced with permission from reference 23. Copyright 1989 Gulf Publishing Company.)...

Figure 6. Effect of particle size on the sampling efficiency of side-wall sampling. (Reproduced with permission from reference 40. Copyright 1985.)...

Sampling of checkpoints during the review exercise confirmed some predictable features, notably that radiography would miss planar defects such as lack of side wall fusion, and that ultrasonic operators tended not to report undercut, porosity or the smaller slag inclusions. 

Another class of anifacts occurs when scanning vertical or undercut features. As the tip approaches a vertical surface, the side wall may encounter the feature before the end of the tip does. The resulting imj e will appear to contain a discontinuous shift. Changing the angle of the tip with respect to the sample s surface can minimize the problem. Side wall imj ing also occurs in STM, but less frequently since an STM tip has a higher aspect ratio than that of an SFM tip. 

Test pits permit visual examination of the soil in place. Such pits also allow manual sampling of undisturbed soil samples. These samples can be taken from the side walls of the pit. 

Other instruments include the Calvet microcalorimeters [113], some of which can also run in the scanning mode as a DSC. These are available commercially from SETARAM. The calorimeters exist in several configurations. Each consists of sample and reference vessels placed in an isothermally controlled and insulated block. The side walls are in intimate contact with heat-flow sensors. Typical volumes of sample/reference vessels are 0.1 to 100 cm3, The instruments can be operated from below ambient temperatures up to 300°C (some high temperature instruments can operate up to 1000°C). The sensitivity of these instruments is better than 1 pW, which translates to a detection limit of 1 x 10-3 W/kg with a sample mass of 1 g. 

Side wall reflections. If the angle of diffraction of an ultrasonic wave leaving a transducer is large enough, reflections may occur from the side walls of the cell. This reflected ultrasound will interact with the ultrasound which has traveled directly through the sample and affects both velocity and attenuation measurements. It is therefore important to calculate the diffraction angle of the transducer and ensure that the side walls are far enough apart so that side-wall reflections do not interfere with the measurements [1]. 

In the case of the water-soluble metallo-host possessing a benzene side-walled, the cavities were observed to self-associate in water to form well-defined dimers which further self-assemble, although solutions in water remained clear up to relatively high concentrations (> 30 mM). Samples of these solutions were studied with TEM and revealed rather ill defined, scroll-like mesoscopic assemblies with lengths up to 10 pm, and a typical width of approximately 100 nm. Enlargement of the receptor side-walls with naphthalene moieties, increases both the hydrophobic character of the hosts and the 7t-7t interactions between the molecules. When the concentration of this naphthalene compound in water was increased to approximately 2 mM, the solution transformed into a turbid dispersion, which remained for days without any precipitation. 

After about 2 yr, some of the cracks were found to have penetrated right through the 14-in-thick casings. The casings are fitted with insulation on the inside (hot gas side). Steel samples cut from the casing walls revealed ... 

Due to their simplicity side-wall samplers are superficially attractive (Figure 1.37) but serious errors in concentration and particle size distribution can arise unless the particles are fine, the concentration is high and a very high sampling velocity is used. A projection extending from the pipe wall only marginally improves sampling efficiency [29]. 

The results discussed so far indicate that the sampling efficiency of a side-wall sampler from a vertical pipeline is always less than unity. One way to increase sample solids concentration is by using a side-wall sampler with a projection see Figure ID). Nasr-El-Din et al. 40) examined the performance of such sampling devices. They found that the projection increased the sample solids concentration. However, the variation of the sampling efficiency with the velocity ratio was different from that obtained with a... 

Figure 9. Effect of sampling velocity ratio on the sample particle size distribution using a side-wall sampler. (Reproduced with permission from reference...

Unlike wall sampling from vertical slurry flows, the sampling efficiency of a side-wall sampler from a horizontal slurry flow may exceed unity in some cases. Nasr-El-Din et al. (42, 43) showed that the sampling efficiency for... 

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