Enhancement cavity, passive

Since its discovery, isolation, and purification in the early twentieth century, insulin has been administered to diabetic patients exclusively by injection until the recent introduction of inhaled insulin. Insulin possesses certain physiochemical properties that contribute to its limited absorption from the gastrointestinal tract, and requires subcutaneous injection to achieve clinically relevant bioavailability. With a molecular size of 5.7 kDa, insulin is a moderately sized polypeptide composed of two distinct peptide chains designated the A chain (21 amino acid residues) and the B chain (30 amino acid residues) and joined by two disulfide bonds. Like all polypeptides, insulin is a charged molecule that cannot easily penetrate the phospholipid membrane of the epithelial cells that line the nasal cavity. Furthermore, insulin monomers self-associate into hexameric units with a molecular mass greater than 30 kDa, which can further limit its passive absorption. Despite these constraints, successful delivery of insulin via the nasal route has been reported in humans and animals when an absorption enhancer was added to the formulation. 

This sensitivity enhancement in detecting small absorptions has no direct correlation with the gain medium and can be also realized in external passive resonators. If the laser output is mode matched (Vol. 1, Sect. 5.2.3) by lenses or mirrors into the fundamental mode of the passive cavity containing the absorbing sample (Fig. 1.11), the radiation power inside this cavity is q times larger. The enhancement factor q may become larger if the internal losses of the cavity can be kept low. 

Because Ni-Mo alloys do not develop a passivating oxide film on the surface, they do not suffer localized attack in the classical sense, such as the halide-induced pitting and crevice corrosion of stainless steels. In some service applications these alloys would not corrode uniformly but might develop some shallow cavities on their surface. These cavities could be the result of confined enhanced corrosion as a consequence of micro galvanic couples with oxidizing agents or other impurities. 

In this case the 200 mm thick reinforced concrete cast in situ slab gives a good inherent resistance against gas ingress. This can be enhanced with a 1200 g DPM and a passive xmderfloor venting layer in accordance witii Table 8.1. However, it should be noted that 1200 g DPM will require sealing with tape at all joints and to service penetrations and across any cavities (if present). It will also require independent inspection to confirm that it has been installed correctly and without defects. 

In contrast to the behavior in solution, valerophenone shows equal quantum efficiencies in frozen solvents. No significant interaction occurs between a solvent molecule and the OH group of a 1,4-biradical in frozen solvents. The frozen solvents provide passive cavities. On the other hand, interfaces of micelles provide active cavities where guest molecules can be oriented through hydrophobic—hydrophilic interactions. The quantum yield for the type 11 reaction of valerophenone in an aqueous hexadecyl tetramethyl ammonium chloride (HTAC) solution is unity. A polar silica-gel surface also provides an active cavity and would enhance the type 11 quantum efficiency. 

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