Aggregation rate limited

The rate of disintegration of the dosage form and the size of the resulting aggregates can be the rate-limiting... 

The coordination of this entire complex process is the province of project management, the objective of which is to ensure that all the necessary parts and components of a project mate up. This discipline in its modem form was first developed for the Polaris missile project in the 1960s. Its major tool that is familiar to pharmaceutical scientists is the network or PERT (Program Evaluation Review Technique) chart, as illustrated in Figure 1.2. This chart is a tool that allows one to see and coordinate the relationships between the different components of a project. One outcome of the development of such a network is identification of the rate-limiting steps, which, in aggregate, comprise the critical path (see Table 1.3 for a lexicon of the terms used in project management). 

Slow aggregation, called Rate Limited Aggregation (RLA), species have a lower sticking probability. Some are able to rearrange and densify the floe, D 2.0-2.2. 

Since transport across the syncytiotrophoblast layer is the rate-limiting step in the absorption of substances from the maternal circulation to the fetal, these cells can provide information on uptake processes which are subject to intracellular regulatory mechanisms or affected by intracellular metabolism. However, it is very difficult to isolate this layer because of its syncytial nature. As a result, the undifferentiated precursor cytotrophoblast cells have been isolated and cultured. These cells do not proliferate in culture, but aggregate and spontaneously differentiate into syncytiotrophoblasts [49],... 

The cross-linked aggregates of MeHNL also showed themselves to be highly active and robust catalysts. Optimized procedures give MeHNL CLEAs with activity recoveries up to 93% measured by a synthetic assay [75]. As observed earlier for PaHNL CLEAs [74], this result is in contrast with the photometric assay, indicating that a fast assay severely underestimates the recovery of initial activity because of rate-limiting diffusion [75]. 

Using Mossbauer spectroscopy to monitor the formation of p-hematin under in vitro reaction conditions, Adams et al. have demonstrated that the reaction is a psuedo-zero-order process [109]. Such a process is consistent with a mechanism whereby a small concentration of heme is kept soluble via acetate, functioning as a phase-transfer catalyst, in a heme-saturated solution. In the rate limiting step, the soluble heme aggregates to P-hematin, which in turn grows until it precipitates from solution. There are clearly complicated heterogeneous reaction equilibria involved in the aqueous chemical formation of p-hematin. Consequently, it should be emphasized that the detailed mechanistic analysis of the complex solubilization of the species involved in the chemical synthesis... 

The aggregation rate is modeled as second-order because dimerization is often the initial step to the formation of aggregates of aggregation number A, with initial dimerization as the rate-limiting step. 

Solid silica spheres are prepared by the Stober8 method. This involves the condensation of TEOS in alcoholic solution of water and ammonia. The mechanism of this synthesis was elucidated by Van Blaaderen et al.20,21 The particle growth is rate-limited by the production of hydrolysed monomer molecules. It involves a surface condensation of monomers and oligomers, while aggregation of particles is only occurring in the early stages of the condensation. 

For soils without appreciable clay aggregation, the experimental results and theoretical analysis described here indicate that when diffusion is rate-limiting, the ratio of the hydrodynamic dispersion coefficient to the estimated soil self-diffusion coefficient may be a useful indicator of the applicability of the local equilibrium assumption. For reacting solutes in laboratory columns such as those used in this study, systems with ratios near unity can be modeled using equilibrium chemistry. 

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