Nucleation stage

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. 

Concerning the nucleation of PE ECC under high pressure, so far two different theories have been proposed. Hikosaka et al. [105-109] suggested that there is no essential difference between the mechanisms of formation of FCC and ECC. At the primary nucleation stage, a... 

In the primary nucleation stage of crystallization at small supercoolings and high pressures, the growth rate G and net transition rate J can be correlated by the following relation ... 

In the secondary nucleation stage, the remaining amorphous portions of the molecule begin to grow in the chain direction. This is schematically shown in Fig. 16. At first, nucleation with the nucleus thickness /i takes place in the chain direction and after completion of the lateral deposition, the next nucleation with the thickness k takes place, and this process is repeated over and over. The same surface nucleation rate equation as the primary stage can be used to describe these nucleation processes. 

As suggested by Barrett (2), it is assumed that following the particle nucleation stage, the polymerization proceeds in the particle (monomer/polymer) phase with no mass transfer limitation. Therefore, the dispersion polymerization is similar to a mass or suspension polymerization, and kj can not be assumed to be constant even at isothermal conditions, since kp and even kp are dependent on the degree of polymerization because of a gel effect. (2., ,D However, since the application of the model is for a finishing step, with polymer molecular weight and viscosity fairly well established, further changes in kp and kp should be minimal. 

If it slow, then nucleation is likely to be due solely to proximity. Model D is an example of volame nucleation idiere decomposition of a solid is involved whereas Model E is that involving gas or liquid nucleation of the solid. Note that if nucleation does not occur, the solid reacts uniformly throughout its whole volume (Model F). However, this mode is rare and the nucleation stages are more likely to occur. We wUl not dwell upon how these nucleation models were derived and will only present the results here. One is referred to Appendix I wherein one can study the mathematics used to obtain the net-result. 

The basic principle of chemical synthesis of nanoparticles is to initiate chemical reactions and control the nu-cleation and growth of the reaction products. In order to achieve monodispersity, LaMer has shown that the separation of the nucleation stage from the growth stage is an important factor to be considered (Figure 1). 

The nucleation stage is followed by two different kinetic regimes of cluster growth (i) a diffusional one (occurring at the earlier stage of growth) which is characterized by a time dependence of cluster radius scaling as where... 

As a result, the energy preference of the local adsorption unit is switched to the opposite distortion/reconstruction and, thus, chiral lateral interactions are switched in the direction of the induction and propagation of the chiral assembly occurring in the mirror image construct, leading to a mirror chiral surface. Therefore, from this work, one may conclude that the overall global or local chirality is determined principally at the nucleation stage. 

A structure formed by the reversible association of am-phiphiles in apolar solvents. In inverted micelles, the polar portion of the amphiphile is concentrated in the interior of the macrostructure. Such association usually occurs with aggregation and is not typically characterized by a definite nucleation stage. Thus, inverted micelles (also referred to as inverse or reverse micelles) often fail to exhibit critical micelle concentration behavior. See Micelle... 

The nucleation stage corresponded to the instantaneous reaction of the C,d2+ ions, initially in equillibrium with the Cd(OH)2, with S2- promptly liberated from... 

The initial nucleation stage of the complex-decomposition mechanism is probably similar to the simple free-anion mechanism. Either ionic or molecular metal species (ion-by-ion) or Cd(OH)2 (cluster) adsorbs on the substrate. However, instead of conversion of the hydroxide to sulphide by topotactic reaction with sulphide ions, the chalcogenide precursor (in almost all studies of this mechanism, that is thiourea) adsorbs on the Cd(OH)2 surface to form a hydroxide-thiourea complex, which then decomposes to CdS. 

Particles smaller than a critical size, which may be referred to as clusters, are formed in the system. Some of these clusters, out of the many that repeatedly come together and part again, may by chance grow larger than the critical size. The process that describes the situation up to the point where the particles reach critical size may be called the nucleation stage. 

After clusters attain a critical size in the system and the nucleation stage is complete, the growth stage commences in a narrower sense. Since the structure is already formed, the solute component will be incorporated into the crystal at the expense of a much smaller energy than that necessary for nucleation. Here, the interface structure between the solid and liquid phases that appeared as a result of... 

Scaling-up by maintaining the droplet size of the granulating liquid will enhance the probability of an uniform nucleation stage to build the granules. 

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