Level measurement characterized displacers

This description of antennas may seem more appropriate to a discussion of radio or television waves. We must realize, however, that at the molecular level dipoles behave exactly like antennas. Since molecules are made up of charged parts, a dipole moment /x is induced by the electric field of the radiation in any material through which radiation passes. In this discussion, the dipole moment equals the product of the effective charge displaced by the field and its distance of separation from the opposite charge. In SI, pi has units C m. We consider isotropic materials characterized by a polarizability a. As the name implies, this property measures the ease with which charge separation —polarity —is induced in a molecule by an electric field. For isotropic substances, the dipole moment and the field are related by the expression... 

The key challenge for the successful use of NMR velocity-imaging techniques to characterize fluid flow properties is the interpretation of the measured parameters. Different experimental strategies provide information about flow processes at different spatial and dynamic scales in porous media. In principle, the flow velocity can be probed either as a local quantity with an image resolution below the pore level,2425 or as a macroscopic flow property corresponding to local volume and temporal averages of fluid molecular displacements.26 One must develop a suitable methodology to correctly determine the parameters that best describe the properties of interest. 

Furthermore, the magnitude of the relaxation modulus is a function of temperature to more fuUy characterize the viscoelastic behavior of a polymer, isothermal stress relaxation measurements must be conducted over a range of temperatures. Figure 15.6 is a schematic log ,(f)-versus-log time plot for a polymer that exhibits viscoelastic behavior. Curves generated at a variety of temperatures are included. Key features of this plot are that (1) the magnitude of EXt) decreases with time (corresponding to the decay of stress. Equation 15.1), and (2) the curves are displaced to lower EXt) levels with increasing temperature. 

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