Wurster modeling

Sandor K, Elekes K, Szabo A, Pinter E, Engstrom M, Wurster S, Szolcsanyi J, Helyes Z (2006) Analgesic effects of the somatostatin sst4 receptor selective agonist J-2156 in acute and chronic pain models. Eur J Pharmacol 539 71-75... 

Mechanistic studies reveal transformations of N, A -disubstituted PD 11 in autoxidized and photo-oxidized polymers and model hydrocarbons [57,58], Wurster s ion radicals 49, associated with ROO in CTC 41 are formed in the first step after electron transfer from 11 [3,24]. 49 is formed regardless of the oxidizing agent and is stabilized via electron delocalization in mesomeric forms [59] ... 

Wurster s Blue perchlorate has been the subject of many investigations. Its stability as a solid and in solution, its ease of preparation, and its symmetry make it an ideal model in spectroscopic and magnetic susceptibility studies. It was one of the first cation radicals to be shown to exist both as a monomer and as a dimer in solution (Hausscr, 1956 Bolton et al., 1962) and in the solid state (Duffey, 1962 McConnell and Lynden-Bell, 1962), the dimeric form being obtainable reversibly by lowering the temperature. This phenomenon is widespread among cation radicals and is discussed in section 3. 

These observations suggest the possible existence of a second oscillator that would be intracellular and would not depend on activation by external cAMP while retaining the capability of being phase shifted by it (Nanjundiah Wurster, 1989). Models based on such an activation cease to oscillate when the cell density is reduced by more than two orders of magnitude. The possibility of a second intracellular oscillator therefore exists the latter could be based on the direct activation of adenylate cyclase by intracellular cAMP (Goldbeter Segel, 1977). An attractive possibility is that the second oscillator involves the autonomous generation of spikes of intracellular Ca (Dupont ... 

The results obtained by Wurster (1982) in Dictyostelium and by Knobil (1980) in the rhesus monkey show, nevertheless, that the frequency of stimulation is as important as the periodic nature of the signal in eliciting an adequate response. The results shown in fig. 8.1 obtained from the model for cAMP synthesis based on receptor desensitization in D. discoideum provide a theoretical basis for these observations. Confirming that the efficiency of the signal is a function of its frequency, these results suggest that the optimum frequency will be dictated by the relative values of the interval between successive stimuli and the time required for receptor resensitization. 

Halloy, J., Y.X. Li, J.L. Martiel, B. Wurster A. Goldbeter. 1990. Coupling chaotic and periodic cells results in a period-doubling route to chaos in a model for cAMP oscillations in Dictyostelium suspensions. Phys. Lett. A. 151 33-6 cmd (Erratum) 159 442 (1991). 

Nanjundiah, V. B. Wurster.1989. Is there a cyclic-AMP-independent oscillator in Dictyostelium discoideum In Cell to Cell Signalling From Experiments to Theoretical Models. A. Goldbeter, ed. Academic Press, London, pp. 489-502. 

The aminoarylation of 9-methylacridinium salts with aromatic amines provides a well-established example of a SET from arylamines to the acridinium ion, as evidenced by the formation of diacridanyl and arylamine radical cation species (Scheme 62). Also, treatment of W-methylacridinium ion with W,W -tetramethyl-para-phenylenediamine, as the model compound, gave the characteristic color of the Wurster s Blue radical cation [11, 136, 137]. 

However, in various coating and granulation experiments a change in the shape of the distribution is observed, for example a dispersion of the distribution. In Fig. 7.45 the results of five different coating experiments are shown, which were conducted in Wurster equipment, a conventional fluidized bed apparatus (FB) in top and bottom spray configuration, and a spouted bed apparatus (SB) in top and bottom spray configuration. Although identical initial conditions were used and the process conditions are comparable (see Tab. 7.6), different final distributions are achieved. This effect cannot be explained by the common model of Eq. 7.34, but it underlines the influence that different types of equipment with different flow patterns may have on the process result. 

A Wurster coater similar to the equipment of Fig. 7.35 was simulated by DPM. The original geometry and the meshed model are shown in Fig. 7.49. 

This contribution outlines a multiscale simulation approach for analysis of a Wurster coating process occurring in a fluidized bed. The processes occurring in the apparatus are described on four different time and length scales The Discrete Element Method coupled with Computational Fluid Dynamics, where each particle is considered as a separate entity and its motion in fluid field is calculated, play a central role in the modeling framework. On the macroscale, the Population Balance Model describes the particle... 

Figure 6 Application of the mesoscale model on Wurster coater.

The real coating process in the studied Wurster coater apparatus with the bed mass of 3 kg contains about 21.8x10 particles with the size of 550 im. Unfortunately, the numerical effort for the calculation of the DPM model increases with increasing the number of simulated particles. The DPM model is unable to represent this number of particles, at least with the actually available computing power. However, the number of particles can be reduced by conservation of the particle and fluid dynamics in the simulated apparatus and its real geometry. In this work a scaling approach proposed by Link et al. (2009) and extended by Sutkar et al. (2013) has been used, in which the scahng of the particle size was carried out. Due to the size increase, the adequate properties of sohd and gas phase have been adapted to keep the dimensionless numbers Archimedes At) and Reynolds Re) and the velocities of minimal fluidization and elutriation constant. 

The sugar pellets SUGLETS produced by Colorcon (UK) are processed in the simulated Wurster coater. These particles are studied in the compression, shear, and impact tests to estimate the material parameters for the Hertz-Mindlin contact model of particles used in DEM on the microscale of the simulation. 

Kadsson S, Rasmuson A, van Wachem B, Bjorn IN CFD modeling of the Wurster bed coater, AIChEJ 55 2578-2590, 2009. 

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