Resistive process resonance

Fig. 1 shows FR spectra for the neopraitane difilusion in sieve fractions of MWCNT-81 sample. When the characteristic time of periodic modulation approaches the time constant of the transport process, resonance occurs, which is indicated by the appearance of an inflexion and a peak in the in-phase and out-of-phase component curves, respectively. In Fig. 1 the component curves of the FR spectrum meet asymptotically at high frequencies. The theoretical analysis of the FR measurement suggested the appearance of this relative curve position is characteristic for rate-controlling diffusion process. However, the rate-controlling transport resistance can not be assigned on the basis of the FR results only to the transport in the macro, meso or micropores of the sample. 

Recall from discussion of the structural design process in Section 7.2 that reconfiguration of the structure is an essential step. Reconfiguration occurs either to increase the capability or to decrease the weight because the structure has more than adequate capability. The term ca-pabi/ity s meant to include margin of safety relative to fracture, adequate resistance to buckling, sufficient difference of excitation frequency from resonant frequencies, etc. 

Once the resist has been patterned, the selected regions of material not protected by photoresist are removed by specially designed etchants, creating the resonator pattern in the wafer. Several isotropic (etching occurs in all directions at the same etch rate) and anisotropic (directional) etching processes are available. Wet chemical etching is an isotropic process that... 

Polysulfone Plastics. These plastics which were commercialized by Union Carbide are actually aromatic polyethers containing periodic sulfone groups which provide additional resonance stabilization. They have good mechanical properties, creep resistance, and dimensional stability but their outstanding quality is their high heat distortion temperature (345°F.) and resistance to thermal oxidative degradation. Limitations are difficult thermoplastic processability, amber color, and sensitivity to organic solvents. 

Heat resistance of organic polymers is far lower than that of metals, ceramics, and glass. There have been major improvements, based on aromatic and heterocyclic resonance, ladder structures, and other mechanisms, and we may see further improvement in the future. Perhaps more serious limitations are the high cost of synthesis and the difficulty of processing these polymers into the desired final products. This is an area where the polymer chemist could use more help from the plastics engineer. 

The changes undergone by US on interacting with a solid, and the information that can thus be obtained from the solid, have been measured mainly through the US velocity and attenuation under resonant conditions. The ultrasonic parameters to be used and their processing are dictated by the final information required. Thus, the resistance to deformation is obtained by calculating the elastic moduli, the number and nature of which are a function of the nature of the solid (e.g. isotropic, anisotropic). However, equations relating the acoustic measurement to sample density, dimensions, material microstructure and thickness can usually be derived from simple parameters such as US velocity... 

---