Quenched state

Equation (A3.3.57) must be supplied with appropriate initial conditions describing the system prior to the onset of phase separation. The initial post-quench state is characterized by the order parameter fluctuations characteristic of the pre-quench initial temperature T.. The role of these fluctuations has been described in detail m [23]. Flowever, again using the renomialization group arguments, any initial short-range correlations should be irrelevant, and one can take the initial conditions to represent a completely disordered state at J = xj. For example, one can choose the white noise fomi (i /(,t,0)v (,t, 0)) = q8(.t -. ), where ( ) represents an... 

For initial post-quench states in the metastable region between the classical spinodal and coexistence curves,... 

The electrochemical machining (ECM) of metals rests on the selective local anodic dissolution of metal. It is used to give metal parts the required shape and size, to drill holes, create hollows, cut shaped slots, and fashion parts of a complex pattern (e.g., the blades of gas turbines). It is an advantage of this method that it can also be used for hard metals (high-alloy steels and other alloys, metals in the quenched state, etc.). 

As shown in Fig. 25, the aged glass typically has a lesser volume in the glassy state compared to the as-quenched state. It is obvious from the data that the longer the aging time, the larger is the amount of volume lost due to sub-Tg annealing. This observation also fits well into the free-volume collapse model discussed earlier. 

Since the optical anisotropy reflects the ordered stacking of aromatic molecules, the anisotropic spheres and the coalesced regions (which can be quite viscous but deformable) are in the liquid crystalline state during the carbonization process. Their quenched state can be described as "liquid crystal glass" according to Diefendorf (9) ... 

Figure 15. a) Partial (calculated, top) and total (calculated, top and measured, bottom) conductivity of Fe-doped SrTiOj in the reversible (regime 1) and in the quenched state (regime 2). At T < T 1 the surface reaction is frozen, b) Reversible and quenched path at lower temperatures. The reversible path is taken when the surface is covered by YBajCUjCW which acts as a catalyst of the surface reaction. According to Ref.68. 

The behavior of unsubstituted stilbene is the opposite Comparison of ps fluorescence decay data [86-88] and fluorescence quantum yields [89] as a function of solvent polarity shows that the nonradiative rates increase in parallel with solvent polarity giving evidence that the quenching state P is more polar than the fluorescing one, E. ... 

Figure 13.20 Master curves of G Tq/T ) versus reduced frequency ajco for the PS-PI block copolymer described in Fig. 13-15 in the high-temperature disordered state and in the low-temperature ordered state flow-aligned into either the parallel or perpendicular directions. The arrows show the time-temperature-shifted frequencies at which the parallel (sideways arrow) and perpendicular (up arrow) orientations are achieved by large-amplitude shearing. The frequency ajcoc 300 secri is the reduced frequency below which G in the disordered and quenched states no longer superpose. (Reprinted with permission from Patel et al., Macromolecules 28 4313. Copyright 1995, American Chemical Society.)...

Studies of Classy Metals in As-quenched State a) Surface Structure and Electronic Properties... 

The thermal stability is a severe limitation if the metallic glass is to be used in as-quenched state for catalysis however, that is not necessarily the case if the glassy alloy is used as catalyst precursor. The thermal stability is mainly influenced by the chemical composition of the metallic glass and the medium to which it is exposed. It has been shown that the crystallization temperature can be significantly lowered in the presence of a hydrogen atmosphere [4.23,24,31,50] or an adsorbed organic compound [4.76]. 

Surface oxidation behavior is particularly important with regard to the use of glassy metals in as-quenched state. A general observation made with binary alloys is that the more electropositive constituent of the alloy tends to segregate to the surface upon oxidation. This procedure can occur already at lower temperature, and consequently the surface of freshly prepared alloys is likely to be covered with a thin layer of oxides of this constituent. This phenomenon has certainly contributed to controversy with regard to the catalytic properties of glassy metal surfaces, since in many of the earlier investigations little care was taken of this behavior and authors tacitly assumed that the surface composition resembles the bulk composition of the quenched materials. 

Fig. 2. Simple two state allosteric model for qE in which the switch between quenched and unquenched conformation is driven by the effect of protonation and de-epoxidation. In this model LHCll can exist in two states, an unquenched conformation and a quenched conformation. Because the affinity of proton and zeaxanthin binding is greater in the quenched state, the ApH and de-epoxidation state will determine the equilibrium between these states. The existence of co-operativity indicates that these two states consist of a group of LHCll subunits which interact and change conformation in concert. The changed conformation, and intersubunit interaction, may give rise to quenching process itself In this model one or moreofthe different LHCll components may be involved.

Heine I and Dau H (1997) The pH-dependence of the Photosystem II fluorescence co-operative transition to a quenching state. Berichte der Bunsen-Gesellschaft-Physical Chemistry 100 2008-2013... 

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