Physicochemical instability

The other rather odd feature of Fig. 3.7.a-l is that for large P, and a narrow range of values, three possible values of ti could be obtained. This behavior is caused by the fact that the heat generation term on the right-hand side of Eq. 3.7.a-2 is a strongly nonlinear function of 7. which can lead to multiple solutions of the equations. This is an example of physicochemical instability, and will be... 

In the first case, the migration of impurities into the solution could initiate physicochemical instability and possibly some potential toxicity. 

Dietary folate intake determines folate nutritional status. It is therefore important to accurately measure folate in food using the best analytical platform currently available. In particular, folate analysis is confounded by several factors, such as the presence of many vitamers, low concentrations, physicochemical instability, and complex sample preparation [12]. It has been reported that the levels of endogenous 5-methyltetrahydrofolate and 5-formyltetrahydrofolate in canned chickpeas, a rich folate source, were 52 and 8 pg/lOO g, respectively [13]. Folate-fortified foods contain higher total folate concentrations than those found in natural folate-rich foods. We recently determined folic acid in Australian fortified bread varieties that was approximately 100 [tg/100 g [14]. 

This equation has been derived as a model amplitude equation in several contexts, from the flow of thin fluid films down an inclined plane to the development of instabilities on flame fronts and pattern formation in reaction-diffusion systems we will not discuss here the validity of the K-S as a model of the above physicochemical processes (see (5) and references therein). Extensive theoretical and numerical work on several versions of the K-S has been performed by many researchers (2). One of the main reasons is the rich patterns of dynamic behavior and transitions that this model exhibits even in one spatial dimension. This makes it a testing ground for methods and algorithms for the study and analysis of complex dynamics. Another reason is the recent theory of Inertial Manifolds, through which it can be shown that the K-S is strictly equivalent to a low dimensional dynamical system (a set of Ordinary Differentia Equations) (6). The dimension of this set of course varies as the parameter a varies. This implies that the various bifurcations of the solutions of the K-S as well as the chaotic dynamics associated with them can be predicted by low-dimensional sets of ODEs. It is interesting that the Inertial Manifold Theory provides an algorithmic approach for the construction of this set of ODEs. 

Similar considerations apply to chemical or physicochemical equilibria such as encountered in phase transitions. A chilled salt solution may be stable (at or below saturation), metastable (supercooled to an extent not allowing nucle-ation), or unstable (cooled sufficiently to nucleate spontaneously). In the case of a solid, S, dispersed in a binary liquid, Li + L2, instability at the instant of formation gives way to a neutral or metastable condition wherein three types of contacts are established ... 

Shale stability is an important problem faced during drilling. Stability problems are attributed most often to the swelling of shales. It has been shown that several mechanisms can be involved [680,681]. These can be pore pressure diffusion, plasticity, anisotropy, capillary effects, osmosis, and physicochemical alterations. Three processes contributing to the instability of shales have to be considered [127] ... 

Combustion of a propellant in a rocket motor accompanied by high-frequency pressure oscillation is one of the most harmful phenomena in rocket motor operation. There have been numerous theoretical and experimental studies on the acoustic mode of oscillation, concerning both the medium-frequency range of 100 Hz-1 kHz and the high-frequency range of 1 kHz-30 kHz. The nature of oscillatory combustion instability is dependent on various physicochemical parameters, such... 

In summary, all features of the liquid rocket engine combustion processes are extensively affected by injector design, and any simplified combustion model, in which the essential three-dimensional nature of the flow processes is ignored, can only be of qualitative significance. Nevertheless, these simplified models are useful in giving us some insight into the nature of the physicochemical phenomena that determine engine performance. In this connection, steady-state combustion rates and overall combustion efficiencies in propellant utilization are far less important practical problems than are control or elimination of instabilities, excessive heat transfer, and hard starts. 

This review, which covers the literature up to mid-1968, presents the knowledge, which is available to date, concerning the molecular and electronic structure of pyrrole. It also surveys the spectroscopic and nonspectroscopic physical properties of pyrrole and its simple derivatives. During the past 25 years, as a result of developments and improvements in instrument design, the literature on the physicochemical properties of organic compounds has expanded rapidly. Mainly as a result of the instability or nonavailability of many compounds, however, the study of pyrroles has lagged somewhat behind... 

Numerous investigations have noted the instability of the physicochemical characteristics of Al(OR)3—the first members of the homologous series, which can display varied physical states, m.p., density, vapor pressure (hysteresis on measurement), viscosity, refraction coefficient, solubility in alcohols, and so... 

Thermal instability of fullerene hydrides makes additional difficulties for investigation of their physicochemical properties, especially at T> 400 K. 

Lipid analyses include both global profiling of the main lipid classes and targeted methods for specific lipid classes which are usually not covered by the global methods due to their low concentrations (e.g., eicosanoids, steroids), instability, or other physicochemical features. Different analytical methods are typically needed for these two approaches. 

In conclusion, drug-excipient compatibility studies have a key role at the early preformulation stages to select excipients or after formulation to help identify the mechanism of any detected instability [14], An understanding of the potential physicochemical interactions of drug with known chemical reactivities of excipients and... 

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