Transition phenomena

Ii90a] Li, W., N.H.Packard and C.G.Langton, Transition phenomena in cellular automata rule space , Physica, 45D (1990) 77-94. 

The theoretical models of effects of recharging of the surface on the band diagram in the surface-adjacent domain of semiconductor adsorbent accompanying adsorption have been developed. The effect of the surface band bending in semiconductor adsorbent on its electrophysical characteristics caused by transition phenomena have been studied. The theories of adsorption-caused response of above characteristics were derived for both ideal monocrystalline adsorbent [4] and monocrystal with... 

Ebner, C. Saam, W. F., New phase-transition phenomena in thin argon films, Phys. Rev. Lett 1977, 38, 1486-1489... 

Equations of state relate the phase properties to one another and are an essential part of the full, quantitative description of phase transition phenomena. They are expressions that find their ultimate justification in experimental validation rather than in mathematical rigor. Multiparameter equations of state continue to be developed with parameters tuned for particular applications. This type of applied research has been essential to effective design of many reaction and separation processes. 

Phase behavior in complex fluids such as polymer blends and block copolymers has been a rich area of the chemical sciences. Near-critical and other transitional phenomena are frequently prominent. Since molecular movement in viscous systems such as these is comparatively slow, phase transitions can be studied more easily in time, and manipulated by quenching and other external influences. Processes for controlled growth of ordered materials are often readily influenced by diffusion, a variety of external fields, and the influence of interacting boundaries, or flow. 

In addition, data on the size, shape and solvation of the polymer particles in aqueous solutions at temperatures below and above the transition phenomena registered by HS-DSC have been obtained [42]. Table 2 shows the results of capillary viscometry and light scattering experiments for the fractions p and s of poly(NVCl-co-NVIAz) synthesized at 65 °C from the feed with the initial molar comonomer ratio equal to 85 15. Since fraction p precipitates from the aqueous solution at temperatures > 34 °C, its intrinsic viscosity can be determined only at 20 °C, whereas for the fraction s such measurements were possible above and below the temperatures of the HS-DSC-registered conformational transition. 

Giitlich, Garcia and Spiering (2003) Spin Transition Phenomena [255]. 

Real, Gaspar, Niel and Munoz (2003) Communication between iron(II) building blocks in cooperative spin transition phenomena [256]. 

Giitlich P, Garcia Y, Spiering H (2003) Spin transition phenomena. In Miller JS, Dril-lon M (eds) Magnetism molecules to materials IV. Wiley-VCH, Weinheim, p 271... 

Roos, Y.H. 1998. Role of water in phase-transition phenomena in foods. In Phase/State Transitions in Foods (M.A. Rao and R.W. Hartel, eds), pp. 57-93. Dekker, New York. 

The technique appears to be particularly useful in the characterization of glass transition phenomena. The utility of MDSC in the study of glass transitions can lead to methods for determination of the amorphous content in a substance [62,63]. 

The application of Landau theory to rock-forming minerals has been promoted by Ekhard Salje and his coworkers in an attempt to achieve better quantification of complex transition phenomena (mainly in feldspars, but also in pyroxenes and spinels Salje etal., 1985 Salje, 1985,1988 Carpenter and Salje, 1994a,b Carpenter, 1988). 

We will see detailed application of Landau theory to complex superimposed transition phenomena when we treat the energetics of feldspars in chapter 5. 

Experimental studies on C2 c pyroxenes (Cameron et al., 1973b Finger and Ohashi, 1976) at temperatures up to E = 1000 °C show that the structure remains stable without transition phenomena, and that the increase of the angle 0 is 2 to 3°. Analogous studies on Pbca pyroxenes (hyperstene, ferrosilite Smyth, 1973) show phase stability in the T range 25 to 1000 °C but a more conspicuous increase in the angle 0 (i.e., 10° for chain A and 15° for chain B in ferrosilite 5° for chain A and 10° for chain B in hyperstene). However, phase transitions have been observed in P2j c pyroxenes. Brown et al. (1972) observed a transition to the form... 

In the case of simple amphiphiles (fatty acids, fatty alcohols, lecithins, etc.), in several cases, transition phenomena have been observed between the gaseous and coherent states of films, which show a very striking resemblance to the condensation of vapors to liquids in three-dimensional systems. The liquid films shows various states in the case of some amphiphiles, as shown in Figure 4.6 (schematic). In fact, if the II versus A data deviate from the ideal equation, then the following interactions may be expected in the film ... 

Current investigations on dilute polymer solutions are still largely limited to the class of macromolecular solutes that assume randomly coiled conformation. It is therefore natural that there should be a growing interest in expanding the scope of polymer solution study to macromolecular solutes whose conformations cannot be described by the conventional random-coil model. The present paper aims at describing one of the recent studies made under such impetus. It deals with a nonrandom-coil conformation usually referred to as interrupted helix or partial helix. This conformation is a hybrid of random-coil and helix precisely, a linear alternation of randomly coiled and helical sequences of repeat units. It has become available for experimental studies through the discovery of helix-coil transition phenomena in synthetic polypeptides. 

Although the statistical mechanical theories such as those described above yield exact analytic expressions for various quantities characterizing the conformation of an interrupted helix, those expressions are so complicated that it is of both theoretical and practical value to simplify them, with the imposition of suitable restrictions on parameters, to forms that are amenable to straightforward computations and also, hopefully, to direct comparisons with observed data. Various attempts have been made, and they are summarized in Poland-Scheraga s book (10). Though not available at the time this book was published, the approximations worked out by Okita et al. (13) are of great practical use for their wide applicability and simplicity. Their method is described below in some detail, because it has been consistently used in our statistical-thermodynamic analyses of helix-coil transition phenomena. 

Figure 5 illustrates, with the data for poly(/J-benzyl L-aspartate) (PBLA) (22), that there are two types of thermal helix-coil transition, normal and inverse. It should be noted that for a given polypeptide the type of transition depends on the solvent in which the polymer is studied. This suggests that polymer-solvent interactions play a decisive role in the helix-coil transition phenomena of polypeptides. 

Paul Ehrenfest suggested a widely used classification of thermodynamic transition phenomena according to the lowest derivative of Gibbs free energy that exhibits a mathematical discontinuity at the phase transition. 

Everything discussed in the present paper shows that the free-volume concept, although very useful from the qualitative point of view, cannot be used for the quantitative description of many properties of polymer systems. This is especially clear when we consider glass-transition phenomena using the idea of the iso-free-volume state. Many experimental data, discussed above, show that this concept cannot be applied even to polymer materials having the same chemical nature but a different physical structure. From the experimental results Goldstein104 had already concluded that the concept of free-volume cannot be correct. These conclusions were carefully discussed later105. ... 

We believe the difficulty is that the free-volume theory as applied to the glass-transition does not take account of the essential role of intra- and intermolecular interaction in the system and the flexibility of the polymer chains, all of which factors play an important role in the glass-transition phenomena. 

At the same time it is evident that the glass-transition phenomena are very complicated and that a different approach and different ideas will be necessary to explain them. This confirms the words written many years ago (in 1899) by the great Russian poet, Valery Briusov, that there are many truths and they often contradict one another . 

Many recent studies on polymer gels are related to volume phase transition phenomena of poly(acrylamide) PAAm gel [7] and poly(N-isopropyl acrylamide) PNIPAAm gel [8, 9]. The volume phase transition in gels was extensively studied by Tanaka and his coworkers [10, 11]. 

In addition to the transition phenomena mentioned so far in the present section, a variety of even larger scale processes might have operated during chemical evolution, namely, instabilities and bifurcations in the very atmospheric environment within which life emerged. As shown in the paper by Marcel Nicolet, the earth s atmosphere is the theater of a variety of complex chemical and transport phenomena. Moreover, as explained by Stanley L. Miller, the composition of the primordial atmosphere has certainly affected deeply the chemistry in the primitive oceans. Conversely, once life emerged the properties of the atmosphere changed radically, and this must have affected the further course of evolution. We refer to Prather et al.41 and North et al.42 for an account of present views on large scale transitions in the earth-atmosphere system. 

It will be apparent from the above discussion that the double-cavity membrane system is ideally suited to investigations of fluctuations and fluctuational transition phenomena. Stochastic resonance and huge noise-induced amplification of a heterodyne signal have been observed. We would emphasize that noise-protected heterodyning is a general phenomenon that may occur in bistable systems of various sorts, and that it may therefore be of interest for applications in engineering. 

First, each person has a large repertoire of these identity states and transits between one and another of them extremely readily, practically instantly. Thus, no obvious lapses or transitional phenomena occur that would make him likely to notice the transitions. 

The next two chapters are devoted to ultrafast radiationless transitions. In Chapter 5, the generalized linear response theory is used to treat the non-equilibrium dynamics of molecular systems. This method, based on the density matrix method, can also be used to calculate the transient spectroscopic signals that are often monitored experimentally. As an application of the method, the authors present the study of the interfadal photo-induced electron transfer in dye-sensitized solar cell as observed by transient absorption spectroscopy. Chapter 6 uses the density matrix method to discuss important processes that occur in the bacterial photosynthetic reaction center, which has congested electronic structure within 200-1500cm 1 and weak interactions between these electronic states. Therefore, this biological system is an ideal system to examine theoretical models (memory effect, coherence effect, vibrational relaxation, etc.) and techniques (generalized linear response theory, Forster-Dexter theory, Marcus theory, internal conversion theory, etc.) for treating ultrafast radiationless transition phenomena. 

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