Nucleation, factors

Particle formation in the early stages of a batch reaction is normally quite rapid. Hence the particle surface area produced is able to adsorb the free emulsifier quite early in the reaction (2 to 10% conversion) and particle formation ceases, or at best slows to a very low rate. Particles formed in the beginning of the reaction would have approximately identical ages at the end of the batch reaction. These particles would be expected to be nearly the same size unless flocculation mechanisms, stochostic differences, or secondary nucleation factors are significant. 

BRAND K, PAGE S, WALLI A K, NEUMAIER D and BAEUERLE P A (1997) Role of nucleat factor kB in atherogenesis Experimental Physiology 82, 297-304. 

Howell, D. S., Pita, J. C., Marquez, J. F., Gatter, R. A. Demonstration of macromolecular inhibitor (s) of calcification and nucleational factor (s) in fluid from calcifying sites in cartilage. J. Clin. Invest. 48, 630 (1969)... 

There is a striking resemblance between Permeation (Chap. 18) and Crystallisation. Just as Permeability is the product of Solubility and Diffusivity (P = SD), the rate of crystallisation is the product of Nucleability (or probability of Nucleation, also called "nucleation factor") and Transportability (Self-diffusivity of chains or chain fragments, also called "transport factor"). This statement is valid as well for the primary nucleation in melt or solution, as for the growth of the crystallites (which is a repeated sequence of surface nucleation and surface growth). 

Due to this unexplained behavior, heterogeneous nucleation is often treated empirically, by simply utilizing a nucleation factor in the exponential in Equation... 

Kitamura (1989) studied many of these nucleation factors in the competitive crystallization of the a and fi forms of L-glutamic acid. He found that at 25 °C only the a modification nucleates and grows. In this system, at least, the effect of temperature on the relative nucleation rates of the two polymorphs is more remarkable than the effect of the supersaturation ratio as the temperature is increased with a constant supersaturation ratio, the amount of a decreases. He also reported that the p form tends to nucleate in stagnant solutions, while at 25 °C essentially only a nucleated homogeneously. 

Kato N, Toukairin M, Asanuma I, et al. Immunocytochemis-tty fot hepatocyte nucleat factor-lbeta (HNF-lbeta) A marker for ovarian clear cell carcinoma. Diagn Cytopathol. 2007 35 193-197. 

Li F, Higgs HN (2003) The mouse Formin mDial is a potent actin nucleation factor regulated by autoinhibition. Curr Biol 13 1335-1340... 

Thus, if the nucleation explanation is correct, it would only be too cold to snow when T decreases well below T /3. This would imply temperatures below 91 K, or -182 °C This is far colder than any recorded temperature on Earth, indicating that the nucleation factor is not an adequate explanation for snowfall suppression at frigid temperatures. The better explanation considers the water vapor capacity of the atmosphere, which decreases exponentially with decreasing temperature. Cold air holds exponentially less water vapor than warm air, and so the precipitation potential decreases dramatically as temperatures become more frigid. This is the main reason why warm snowstorms, where the air temperature is just slightly below the freezing point, typically produce the greatest snowfall rates. 

In 1-14 weeks after withdrawing treatment bile reverts to its supersaturated state (13). Since other factors (obesity, pregnancy, diurnal variation of biliary cholesterol saturation, presence of nucleating factors, etc.) are required for gallstone recurrence, a supersaturated bile does not necessarily mean gallstone recurrence, but does represent a high risk factor. 

The following expression is then derived for regime 111 growth. It is noted that the nucleation factor, the last exponent in eq. (8.75), is the same as that for regime 1 (cf. eq. (8.64)) ... 

The central quantity of interest in homogeneous nucleation is the nucleation rate J, which gives the number of droplets nucleated per unit volume per unit time for a given supersaturation. The free energy barrier is the dommant factor in detenuining J J depends on it exponentially. Thus, a small difference in the different model predictions for the barrier can lead to orders of magnitude differences in J. Similarly, experimental measurements of J are sensitive to the purity of the sample and to experimental conditions such as temperature. In modem field theories, J has a general fonu... 

For these sequences the value of Gj, is less than a certain small value g. For such sequences the folding occurs directly from the ensemble of unfolded states to the NBA. The free energy surface is dominated by the NBA (or a funnel) and the volume associated with NBA is very large. The partition factor <6 is near unify so that these sequences reach the native state by two-state kinetics. The amplitudes in (C2.5.7) are nearly zero. There are no intennediates in the pathways from the denatured state to the native state. Fast folders reach the native state by a nucleation-collapse mechanism which means that once a certain number of contacts (folding nuclei) are fonned then the native state is reached very rapidly [25, 26]. The time scale for reaching the native state for fast folders (which are nonnally associated with those sequences for which topological fmstration is minimal) is found to be... 

Interleukin-1 OC and (3. IL-1 has radioprotective activity toward BM and other tissues (151,164). IL-1 is produced in response to endotoxin, other cytokines, and microbial and viral agents, primarily by monocytes and macrophages. Other nucleated cells can also produce it. IL-1 appears to play an important role in the regulation of normal hemopoiesis directly by stimulating the most primitive stem cells and indirectly by stimulating other hemopoietic factors, including G-CSF, GM-CSF, M-CSF, and IL-6. 

Both homogeneous and heterogeneous mechanisms requite relatively high supersaturation, and they exhibit a high order dependence on supersaturation. These factors often lead to production of excessive fines ia systems where primary aucleatioa mechanisms are important. The classical theoretical treatment of primary nucleation results ia the expressioa (5) ... 

TFIIA and TFIIB are two basal transcription factors that are involved in the nucleation stages of the preinitiation complex by binding to the TBP-TATA box complex. Crystal structures of the ternary complex TFIIA-TBP-TATA box have been determined by the groups of Paul Sigler, Yale University, and Timothy Richmond, ETH, Zurich, and that of the TFIIB-TBP-TATA box by Stephen Burley and collaborators. The TBP-DNA interactions and the distortions of the DNA structure are essentially the same in these ternary complexes as in the binary TBP-TATA complex. 

The properties of a given polymer will very much depend on the way in which crystallisation has taken place. A polymer mass with relatively few large spherulitic structures will be very different in its properties to a polymer with far more, but smaller, spherulites. It is thus useful to consider the factors affecting the formation of the initial nuclei for crystallisation (nucleation) and on those which affect growth. 

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