Water, generally supercooled

In Section VII we conclude our results and discuss several issues arising from our proposals. We revisit our original motivation—that is, to find a simple model, in the sense of dynamical systems, that captures several common aspects of slow dynamics in liquid water, or more generally supercooled liquids or glasses. Our attempt is to make clear the relation and compatibility between the potential energy landscape picture and phase space theories in the Hamiltonian dynamics. Importance of heterogeneity of the system is discussed in several respects. Unclarified and unsolved points that still remain but should be considered as crucial issues in slow dynamics in molecular systems are listed. 

We may list differences between the liquid water system and the FPU model the latter will be examined in the next section as a representative system in the study of many-dimensional Hamiltonian systems. The most important difference would be that the FPU model describes a lattice vibration around an equilibrium point and the potential energy function possesses a single minimum, whereas there are infinitely many local potential minima and the potential energy landscape generally becomes ragged in the case of the liquid water system. The reason why the character of the potential landscape could be so important is that the raggedness is considered as an origin of slow motions in liquid water or supercooled liquids. 

Equilibrium vapor pressure is the vapor pressure of a system in which two or more phases or a substance coexist in equilibrium. In meteorology, the reference is to water substance, unless otherwise specified, If the system consists of moist air in equilibrium with a plane surface of pure water or ice, the more specialized term saturation vapor pressure is usually employed, in which case, the vapor pressure is a function of temperature only. In the atmosphere, the system is complicated by the presence of impurities in liquid or solid water substance (see also Raoult s Law), drops or ice crystals or both, existing as aerosols and, in general, the problem becomes one of nucleation. For example, the difference in vapor pressure over supercooled water... 

In general, intracellular freezing induced with extracellular ice crystal initiates around -5°C and most freezable water freezes by the time the cells reach -20°C. Thus, freezing injury of the cells should be concentrated in this temperature region. On the other hand, water molecules cannot endure in a supercooled state under —40°C even if there is no seeding of ice crystals. This suggests that reduction of cell viability is restricted to temperatures above -40°C. The results shown in Figure 9, also support this conjecture. 

We did not find any evidence of free volume channels in the mixtures of water and glucose, consistent with previous results of a study for water-sucrose in a broader range of water content (Molinero et al., 2003). The existence of such charmels, and the role of free volume in the dynamics of mixtures of oligosaccahrides with a high degree of polymerization deserve further study. The results presented here for water relaxation in supercooled DP12 allows us to generalize the observed mechanism for water diffusion in... 

The objective of this paper is to provide a theoretical framework for understanding the melting, freezing, and supercooling behavior of water in small dusters and droplets. Although attention will be focussed on spherical geometry, the basic ideas involved can be generalized to other shapes. 

It is perhaps worth while to have a further look at the ice-like clusters which play such an important part in all these theories. In the interests of simplicity they have generally been considered to have a crystalline structure like that of Ice Ih or I but such a requirement is unnecessary and, in view of the supercooling of liquid water which we shall consider presently, unlikely. From the point of view of the cluster theories discussed above, the only requirement on the clusters is that they have substantially tetrahedral bonding and the same sort of molecular volume and vibrational... 

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