Wave propagation, transport properties

Following is a resume of paper by Fickett (Ref 2) If a cylinder of explosive is suddenly heated or struck at one end, a detonation wave propagates down the length of the charge with approximately constant velocity. This phenomenon is often treated by the model of von Neumann-Zel dovich. Transport properties are neglected, and the wave consists of a plane shock followed by a short reaction zone of constant length in which the explosive material is rapidly transformed into decomposition or detonation products. 

Transport properties such as wave propagation, diffusion, and conduction are known to depend strongly on material properties, but also on geometrical constraints and dimensional confinement. It is very challenging, especially in mesoscopic systems like ultrathin films, to determine the origin for exotic, not bulk-like, transport properties. 

Phenomenological theories fail to describe transport and material properties of small ensemble systems, i.e., systems in which the number of molecules is smaller than Avogadro s number. Within the last century, it has been theoretically predicted and experimentally confirmed that small ensemble systems generate some sort of quantum confinement, in which optoelectronic, electronic, and magnetic wave propagation experience quantized nanoscale size effects. 

The process is not instantaneous a wave propagates with a speed v, which depends on the properties of the medium. However, it must be noted that no transportation of the medium s particles take place, particles oscillate around their permanent equilibrium positions. 

Present theoretical efforts that are directed toward a more complete and realistic analysis of the transport equations governing atmospheric relaxation and the propagation of artificial disturbances require detailed information of thermal opacities and long-wave infrared (LWIR) absorption in regions of temperature and pressure where molecular effects are important.2 3 Although various experimental techniques have been employed for both atomic and molecular systems, theoretical studies have been largely confined to an analysis of the properties (bound-bound, bound-free, and free-free) of atomic systems.4,5 This is mostly a consequence of the unavailability of reliable wave functions for diatomic molecular systems, and particularly for excited states or states of open-shell structures. More recently,6 9 reliable theoretical procedures have been prescribed for such systems that have resulted in the development of practical computational programs. 

Apart from acoustic phonons, which account for heat transport in insulating media, propagation of vibrational energy is usually not considered in crystals, as the dispersion of optical modes is normally very small over the Brillouin zone. However, there is an important class of optical vibrations in crystals for which spatial propagation can be the dominant property at optically accessible wave vectors. This class is identical with that of infrared active modes and its members are known as phonon-polaritons. ... 

The formalism (Chapter 4) developed to derive lattice and molecular dynamics from optical and neutron spectroscopy is but a necessary first step towards deriving a sound mechanistic basis for the equations of state of the azides (Chapter 9). Through the study of molecular dynamics and the effect of pressure and temperature it may eventually become possible to treat quantitatively the manner in which the crystals absorb, release, and transport energy, and to seek in the inherent properties of the lattice and molecules the mechanism by which reaction waves develop and propagate. 

For high Da the column is dose to chemical equilibrium and behaves very similar to a non-RD column with n -n -l components. This is due to the fact that the chemical equilibrium conditions reduce the dynamic degrees of freedom by tip the number of reversible reactions in chemical equilibrium. In fact, a rigorous analysis [52] for a column model assuming an ideal mixture, chemical equilibrium and kinetically controlled mass transfer with a diagonal matrix of transport coefficients shows that there are n -rip- 1 constant pattern fronts connecting two pinches in the space of transformed coordinates [108]. The propagation velocity is computed as in the case of non-reactive systems if the physical concentrations are replaced by the transformed concentrations. In contrast to non-RD, the wave type will depend on the properties of the vapor-liquid and the reaction equilibrium as well as of the mass transfer law. 

A phonon is a lattice vibration that mediates transport of sound and thermal waves. A phononic crystal is a periodic material engineered to control the propagation of phonon waves. Phononic crystals that manipulate sound waves are sometimes called acoustic metamaterials. As for photonic crystals, BCP SA may be used for fabricating phononic crystals. Also similar to the photonics field, one of the main properties that scientists try to establish in acoustic metamaterials is a phononic band gap, i.e., a frequency range in which phonons cannot exist in the material. Similarly to photonic crystals, phononic crystals can manipulate specific phonons with a wavelength that is comparable to the lattice dimension. For example, a periodic material with a lattice dimension of centimeters manipulates sound waves, whereas a material with a lattice dimension of nanometers strongly interacts with thermal waves. Thus, a phononic crystal derived from BCP SA may be able to control the flow of thermal waves. 

---