Nucleation, multistep

SO4 in cloudwater Washout, rainout Dry deposition Cloud nucleation COS + OH multistep - HzS MSA - sol by some mechanism... 

Rapid polymer transport and associated structured flow formation are multistep processes. These processes may include 1) initial diffusion of components across the boundary 2) inversion of density, 3) convective motions occurring in regions that are unstable with respect to density, 4) birth and nucleation of structured flows, 5) development of visible structured flows, and 6) movement and maintenance of structured flows over longer periods. A clear delineation of any of these steps has not been achieved so far. Future work will be concerned with the development of systems in which these individual steps may be studied in more detail. 

These equations give the general solution to the problem of multistep nucleation when the rate constants are all different at the start, but after the nucleus contains more than r atoms, the nucleation rate constants have a constant value k for the addition of successive atoms of product- The limit for short times may be obtained by induction as before, and they obtain... 

Suppose that nucleation is a multistep process characterized by rate constants k0, ku kp, and that once a nucleus containing p atoms of product is formed it becomes an active growth nucleus. The rate of formation of active growth nuclei is therefore... 

This is the general solution to the problem of multistep nucleation followed by a constant rate of growth in three dimensions. Equation (113) is of the same form as Eq. (107) and therefore is called the generalized Avrami equation. The limit for short times is... 

One of the first steps to go behind the metastatic cascade is the examination of peripheral blood to detect potential circulating malignant cells. This method is useful to follow-up malignancies spreading via the blood stream such as sarcomas, melanoma, neuroblastoma, prostatic, thyroid and hepatocellular carcinomas. PCR-and RT-PCR-based molecular techniques are found to be the most efficient assay to detect circulating tumor cells in peripheral blood, and allow the detection of one tumor cell in up tolO background nucleated blood cells. However, it is important to consider that the presence of tumor cells in peripheral blood is only one step in a multistep process and not all tumor cells circulating in peripheral blood are able to... 

The electrode reaction may involve the formation of a new phase (e.g. the electrodeposition of metals in plating, refining and winning or bubble formation when the product is a gas) or the transformation of one solid phase to another (e.g. reaction (1.5)). The formation of a new phase is itself a multistep process requiring both nucleation and subsequent growth, and crystal growth may involve both surface diffusion and lattice growth. 

In Kinetics and Thermodynamics of Multistep Nucleation and Self-Assembly in Nanoscale Materials, eds Nicolis, G., Maes, D. John Wiley Sons, Inc. Hoboken, N.J. 

The overview provided above covers the classical perspective on crystallization and particularly nucleation. A rapidly growing body of work shows that this view is not complete. The alternative model for nucleation is often termed the two-step nucleation theory. In brief, this model sng-gests that nucleation is a multistep process where the first step involves phase separation via the formation of liquid or amorphous nanoparticles. This is then followed by crystallization within this particle. The activation energy for each of these steps is relatively small, and it is expected that the overall process would be faster when compared with a single-step (classical) process with the same overall activation energy. Experimental and theoretical evidence supports this mechanism, and it has been suggested that the nucleation process is likely to proceed in this way in most, if not all, cases. ... 

Zhang et al. used Langmuir monolayers to study the initial stage of nucleation and crystallization of calcium phosphate [160]. The monolayers used in their study consisted of dipalmitoylphosphatidylcholine, arachidic acid, and octadecylamine. The experiments show that the adsorption of calcium ions to the respective mono-layer is a prerequisite for subsequent nucleation. The authors also demonstrate that calcium phosphate forms through a multistage assembly process, in which first an amorphous calcium phosphate dihydrate layer forms, which then recrystallizes to form a crystalline hydroxyapatite layer (Fig. 12). This transformation of an amorphous phase to a crystalline phase provides direct evidence of a multistep crystallization process, which the authors claim is similar to the processes occurring in biomineralization. 

Nucleation on adsorbed monomer M and dimer D dye, with simultaneous independent micellization. This mechanism is the same as 6) but with the additional D-adsorption equilibrium and the following multistep sequence... 

The first kinetic studies carried out by slow temperature jump experiments (Pohl, 1968a,b, 1969, 1972a,b, 1976), followed by kinetic analyses reported by Baldwin and co-workers (see Baldwin, 1975) originated the interpretation of the folding process in terms of sequential steps of reactions. It was proposed that the first one, nucleation, is dominated by entropy. Progressively, it was accepted that protein folding is a multistep process and the identification of intermediates became an important goal in the study of the formation of protein structure. 

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