Structural impedance

This effect is not simply due to the better packing possible with the branched isomers. The lumpy brcuiched structures impede rotation about the carbon-carbon bond on the main chain, thus giving a stiffer molecule with consequently higher transition temperature. 

The slow and incomplete retraction of the solutions containing n-propylamine is attributed in part to the presence of weakly-held polysiloxane material on an underlying, more coherent film. The fact that the solution retracts at a low contact angle (about 20° to 30°) cannot completely explain the inordinately slow retraction. It is more likely that a loose, gel-like polymeric structure impedes and in some instances prevents the withdrawal of the retracting liquid. When retraction failed to occur, the residual solution was easily displaced by water. Undoubtedly, this displacement is a complex process of desorption, liquid-liquid displacement and hydrolysis of the polymer film. 

High frequency applications in which the wavelength is comparable to the scale of the composite macrostructure, show the full potential of composite structures. Impedance, bandwidth, and radiation pattern can be controlled in such systems in a sophisticated manner impossible in single-phase systems. By prepoling PZT fibers or ribbons before the assembly of the composite, it is possible to construct polar solids of new type for use in complex transducer arrays operating in scanning and focusing modes. 

For the reasons outlined above, some typical acid-catalysed reactions, such as hydration and etherification, may be better performed over non-microporous acid catalysts, but microporous acids have found uses in this area. Asahi, for example, have established the zeolite-catalysed hydration of cyclohexene as a commercial process, " where in a two-phase reaction mixture (aqueous and non-aqueous layers) the H-ZSM-5 catalyst stays in the aqueous phase but adsorbs enough cyclohexene, because of its relative hydrophobicity, that the reaction proceeds in the zeolite pores. This has the advantage over the previously used cyclohexene/sulfuric acid system that the aqueous layer is not acidic and corrosive. Furthermore, the medium-pore structure impedes etherification to dicyclohexyl ether and the highly siliceous zeolite has long-term stability in boiling water. 

The adaptronic approach would be one that would borrow directly from the biological world. Materials that behave more or less like muscles can be used in adaptronic structures and are called induced strain actuators. When energy is applied to the actuators, they attempt to expand/contract and work against any load that is applied to them. The actuators are typically bonded to the surface of a structure, or embedded within the material. This means that the artificial muscles must now work against the inherent structural impedance of the component, just as hmnan muscles are parallel to the skeletal structure or bone. However, whereas the arm has discrete joints about which rotation occurs, the adaptronic structure may be a continuum, thereby necessitating a distributed actuation system. For example, the tip motion of a beam will not occur by rotating the beam about a joint but by inducing its deformation by means of induced strain actuators placed on the beam. 

During its lifetime the press felt runs several million times through the press nip. Reduction in felt thickness, abrasion and contamination are the main reasons why a press felt has to be replaced. Fillers such as calcium carbonate, clay/kaolin, other papermaking additives, and adhesives e. g. from recovered paper deposit in the press felt structure, impeding or even locally preventing water flow. In some cases not even alkaline and acids can re-open the press felt structure. 

The oxonium ion shown below, with its positive oxygen attached to three tertiary carbons, is stable and immune to solvolysis Evidently, its tightly constrained structure impedes unimolecular C-O bond cleavage that would give a carbocation. Basic nucleophiles give an E2 product. Equally surprisingly, azide, N3, attacks the tertiary center by Sn2, the only such case reported in the literature. 

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