Transmission techniques, high-pressure

Compared to other biomolecular systems, lipid bilayer membranes and lyotropic lipid mesophases in general have been shown to respond most sensitively to hydrostatic pressure. The methods used in the high pressure studies have mainly included X-ray and neutron diffraction, fluorescence, IR and Raman spectroscopy, light transmission and volumetric measurements. Only a small amount of work has been performed using NMR techniques combined with high-pressure, a field which was pioneered by Jonas and co-workers " although the method is very powerful, non-invasive and allows the study of a series of structural and dynamic properties of the systems in detail and with atomic resolution. 

Vibrational spectroscopy is the method of choice for the characterizing functional groups in complex organic molecules. Infrared transmission spectroscopy has been used on dried humics pressed into KBr pellets to determine the relative carboxylate content of humic materials (14-16). However, interferences arise from the presence of water bands and possible alterations of the samples under the high pressures used to form the pellets. Diffuse-reflectance techniques can avoid some of the difficulties associated with the KBr pressed-pellet method (9,17-18). To obtain a spectrum analogous to an absorption spectrum, the data are transformed from reflectance units to Kebulka-Munk (K-M) units. However, K-M units are related to... 

Transmission spectroscopy (2) is the simplest sampling technique in IR spectroscopy and is used for routine spectral measurements on diverse samples. Resin samples such as polystyrene or TentaGel (3) beads are usually prepared as a potassium bromide disc (pellet). A small amount, usually 1-3 mg, of finely ground solid sample is mixed with approximately 400 mg powdered potassium bromide and then pressed in an evacuated die under high pressure. The resulting discs are transparent and yield good spectra. 

The alkali-halide disk method The alkali-halide disk technique is another traditional transmission sample presentation method, in which an intimate mixture of the finely ground solid sample and dry powdered alkali-halide, most commonly KBr, is pressed into a self-supporting disk. Finely powdered dry potassium bromide will coalesce to form a clear disk with high transmission when it is pressed under high pressure in an evacuated die. 

Fig. 12.20e). The PL intensity and full width at half maximum of BaTiFeiMn" " and ruby Al203 Cr were compared using a neon pressure-transmission medium. BaTiFsiMn" " exhibited stable emission behavior under a high pressure up of to 40 GPa. This demonstration indicates that Mn" -doped fluorides are alternative candidates as a potential pressure gauge for high-pressure techniques. 

The gas permeability characteristics of a film may be determined by using it as a barrier to separate two chambers that contain the gas at different concentrations. In the extreme case one of the chambers is evacuated. The rate of gas permeation across the barrier can be determined from changes in pressure or volume in the low concentration chamber or by analytical techniques that measure the concentration of the gas of interest in an inert carrier gas on the low concentration side of the barrier. When pressure is used to measure the permeation rate, the low concentration chamber is evacuated and the high pressure side is flooded with pure gas. The rise in pressure is monitored with a manometer, from which the rate of permeation can be calculated and thus the gas transmission rate. When the volumetric method is used, a pressure differential is maintained across the barrier and the movement of a slug of liquid in a capillary tube is followed to determine the volume of gas crossing the barrier. 

A limited number of stodies have been conducted on the internal repair of steel pipelines using composite material systems. As a consequence, only a few industries have used composite technologies for internal repair. In their report, Bruce et al. (2006) indicated that internal repair would have the best economics for underwater repair locations as it reduces out-of-service time and does not require divers and habitats. Such economics arise because the majority of the gas transmission line companies in the United States consider the ability of the pipeline to remain in service during internal repair to be very important. Moreover, they would considCT internal repair, even if the pipeline needs to be out of service (no flow), only if the pipeline remains pressurised and the line can still be inspected by a pipe inspection gauge after repair. However, these companies have indicated that they would consider performing a repair from inside the pipe once a proven and accepted internal repair system becomes available. Thus, the selection of the most appropriate technique of renovation, particularly on the internal repair of high-pressure and deep water pipeline applications, is a critical and ongoing issue. 

Ultem PEI resins are amber and amorphous, with heat-distortion temperatures similar to polyethersulfone resins. Ultem resins exhibit high modulus and ate stiff yet ductile. Light transmission is low. In spite of the high use temperature, they are processible by injection mol ding, stmctural foam mol ding, or extmsion techniques at moderate pressures between 340 and 425°C. They are inherently flame retardant and generate Httie smoke dimensional stabiUties are excellent. Large flat parts such as circuit boards or hard disks for computers can be injection-molded to maintain critical dimensions. 

---