Transitioning possessions

Reconstructive phase transitions occur when major changes are made in the topology, i.e. when the bond graph is reorganized. The transitions usually observed in structures with lattice-induced strain are displacive and often second order (no latent heat). Reconstructive transitions arise when two quite different structures with the same composition have similar free energies. Unlike the displacive transitions they involve the dissolution of one structure and the recrystallization of a quite different structure. These phase transitions possess a latent heat and often display hysteresis. 

It should be taken into account that even while the spin-flop transition possesses the character of a 1-st order phase transition at a precise alignment of the magnetic field along the z-axis, the character of the 1-st order transition is lost when h tilts away from the z-axis by an angle larger than a certain critical value ipc. The critical angle value is deter-... 

However, these criteria are not as general as claimed by the authors. As is demonstrated in the next section, metal dissolution reactions that oscillate at the active passive transition possess all the characteristics of N-NDR oscillators, but do not comply with Strasser et al. s mechanistic ingredients. Hence, the above conditions (a) and (b) are sufficient, but not necessary. 

It is still uncertain whether or not the solid-hquid equihbrium Hne terminates at a critical point. Munster has recently given theoretical reasons for behoving that all first-order transitions possess a critical point, but this conclusion is contrary to that reached by Domb, j"j whose theory predicts the absence of a solid-fluid critical point. The experimental work of Simon and his co-workers on the melting line of hehum shows no evidence for a critical point up to a pressure of 9,000 atm. and a temperature of 56° K. Alder and Jura have, however, made calculations which suggest that a soHd-fluid critical point should... 

The same t3q)e of analysis can be applied to (m- j ) transitions. Again examination of Fig. 4 shows that the (m->0) transition possesses the greatest vibrational overlap. Transitions of type (m->j ) with j > 0 possess vibrational overlaps which decrease as j increases. In cases where i approaches n, 9i 9i oscillates rapidly and (i j ) 0. 

Moreover, it is also interesting to find that the unit cell dimensions along the a- and -axes show small, but sudden, changes at the transition temperature of e Sj7->Sg. Their first derivatives with respect to the temperature, the coefficients of mermal expansion of those axes, also exhibit discontinuous changes (S,Jjy This clearly indicates that this transition possesses the characteristics of a thermodynamic first-order transition (4). 

Sometimes it is stiU debated whether the glass transition is a purely kinetic transition or a second-order thermodynamic transition (van Krevelen 2003). On one hand, it is true that the crystallization process for a number of (atactic) polymers would not take place even at infinite time, and this transition possesses the characteristics of a second-order thermodynamic transition (at least formally, in the Ehrenfest sense see definition of the phase transition in Section 2.2). But the absence of crystallization does not prove that the glass transition is a thermodynamic second-order transition, and it is also true that the glass transition does not occur as a definite sharp transition as would be required by equilibrium thermodynamics. Therefore, the glass transition must be considered a kinetic transition. 

Fig. 6.7 Schematic lepiesentation of the change in electronic distribution induced in a molecule by the electromagnetic field in the case of an electric dipole transition (a), a magnetic dipole transition (b) and a transition possessing a rotaUny strength (c). In the latter case the transition is associated with the phenomenon of optical activity...

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