Phase caveat

A detailed descriphon of octanol-water distribuhon coefficient measurements by shake-flask can be found in publications by Dearden [2] and Hansch [24], The method usually involves the following solubilization of the compound in a mixture of mutually presaturated buffered water and octanol, agitation unhl equilibrium has been reached, careful separation of octanol and aqueous phases, and direct measurement of the solute concentration in both phases. Although seemingly simple, the method has a number of caveats making it inappropriate for some compounds. 

Though both miscible and immiscible blends are composite materials, their properties are very different. A miscible blend will exhibit a single glass transition temperature that is intermediate between those of the individual polymers. In addition, the physical properties of the blends will also exhibit this intermediate behavior. Immiscible blends, on the other hand, still contain discrete phases of both polymers. This means that they have two glass transition temperatures and that each represents one of the two components of the blend. (A caveat must be added here in that two materials that are immiscible with very small domain sizes will also show a single, intermediate value for Tg.) In addition, the physical properties... 

As the digging task relies upon external motivation, investigators should be careful not to misinterpret the results. For example, if different strains of mice spend different amounts of time digging in the CS+ during the test phase of the experiment, this should not be interpreted to mean that one strain has learned more than another strain (Schellinck et al. 2001). It is possible that the different strains are more sensitive to food restriction, however mild, or have different levels of activity. Both factors could lead to increased digging. With this caveat, the task is very useful for assessing acuity and long-term memory. 

The other mode of application, known as surprisal synthesis is the more fundamental one. It starts from the distribution of initial conditions = the distribution in the initial phase space. As I argued, most of the details of this distribution are irrelevant for obtaining a reproducible final distribution of interest. (Again the caveat all... 

D. Washo-Stultz, C. Crowley, C. M. Payne, C. Bernstein, S. Marek, E. W. Gerner and H. Bernstein, Increased susceptibility of cells to inducible apoptosis during growth from early to late log phase an important caveat for in vitro apoptosis research, Toxicol. Lett., 2000, 116(3), 199. 

A final caveat that must be applied to phase diagrams determined using DFT calculations (or any other method) is that not all physically interesting phenomena occur at equilibrium. In situations where chemical reactions occur in an open system, as is the case in practical applications of catalysis, it is possible to have systems that are at steady state but are not at thermodynamic equilibrium. To perform any detailed analysis of this kind of situation, information must be collected on the rates of the microscopic processes that control the system. The Further Reading section gives a recent example of combining DFT calculations and kinetic Monte Carlo calculations to tackle this issue. 

The factors that control separation and dispersion are quite different. The relative separation of two solutes is solely dependent on the nature and magnitude of the Interactions between each solute and the two phases. Thus, the relative movement of each solute band would appear to be Independent of column dimensions or particle geometry and be determined only by the choice of the stationary phase and the mobile phase. However, there is a caveat to this statement. It assumes that any exclusion properties of the stationary phase are not included in the term particle geometry. The pore size of the packing material can control retention directly and exclusively, as in exclusion chromatography or, indirectly, by controlling the access of the solute to the stationary phase in normal and reverse phase chromatography. As all stationary phases based on silica gel exhibit some exclusion properties, the ideal situation where the selective retention of two solutes is solely controlled by phase interactions is rarely met in practice. If the molecular size of the solutes differ, then the exclusion properties of the silica gel will always play some part in solute retention. 

Given these caveats, we first treat the case of adsorption to a solid surface, and then absorption into a liquid particle or liquid surface layer on a particle. As we shall see, the distribution of SOC between the gas and condensed phases can be used to infer the nature of the sorbent sites. 

There is an important caveat. These, and other experimental values cited for the gas- and particle-phase concentrations of semivolatile PAHs, do not necessarily represent their actual equilibrium concentrations in the ambient air being sampled. Thus, there can be both positive and negative artifacts associated with the sampling methodologies. Furthermore, sorption equilibrium may not be achieved in the polluted ambient air. 

Before proving the phase rule (7.6), we list some elementary guidelines and caveats regarding the definitions (7.7a-c) ... 

We have previously emphasized (Section 2.10) the importance of considering only intensive properties Rt (rather than size-dependent extensive properties Xt) as the proper state descriptors of a thermodynamic system. In the present discussion of heterogeneous systems, this issue reappears in terms of the size dependence (if any) of individual phases on the overall state description. As stated in the caveat regarding the definition (7.7c), the formal thermodynamic state of the heterogeneous system is wholly / dependent of the quantity or size of each phase (so long as at least some nonvanishing quantity of each phase is present), so that the formal state descriptors of the multiphase system again consist of intensive properties only. We wish to see why this is so. 

There is one significant caveat to this. Allocations during phase II should not create promises about allocations post-2012 that foster inefficiency, or undermine the options post-2012. The risk of perverse incentives arising from expectations about continued free allocation has already been... 

The essential question that we address in this section is How well can the various types of ab initio and density functional calculations predict heats of formation However an important caveat must be added Our eventual interest will not be in normal, typical molecules, but rather in those metastable ones that show potential as energetic materials. The present discussion will focus upon gas phase AHf we will return later to the conversion to liquid and solid phase values. 

Asa caveat to the considerations involving the solid phase it should be mentioned that some solids undergo mesomorphic changes before melting (although these have been assumed not to occur in the solids so far discussed). 

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