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Population Balance Approach (population + balance_approach)
Selected AbstractsThe effect of cell size distribution during the cooling stage of cryopreservation without CPAAICHE JOURNAL, Issue 8 2010S. Fadda Abstract A novel model capable of quantitatively describing and predicting intracellular ice formation (IIF) as a function of temperature in a cell population characterized by a size distribution is proposed. The model overcomes the classical approach which takes into account a population of identically sized cells. The size distribution dynamics of a cell population in response to water osmosis and IIF occurrence during the cooling stage of a standard cryopreservation protocol without using cryoprotective agent (CPA) is simulated by means of a suitable population balance approach. Specifically, the model couples the classical water transport equation developed by Mazur1 to the quantitative description of nucleation and diffusion-limited growth of ice crystals in the framework of a 1-D population balance equation (PBE). It is found that IIF temperature depends on the cell size, i.e., it is higher for larger cells. Correspondingly, the probability of IIF (PIIF) results to be dependent on the initial size distribution of the cell population. Model's parameters related to the osmotic behavior of the cell population and to IIF kinetics are obtained by comparison between theoretical results and suitable experimental data of isolated rat hepatocytes available in the literature. Model reliability is successfully verified by predicting the experimental data of PIIF at different, constant cooling rates with better accuracy as compared to the theoretical approaches available in the literature. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Flocculation of biological cells: Experiment vs. theoryAICHE JOURNAL, Issue 7 2003Binbing Han Flocculation of biological cells is important in the biotechnology industry, as it could lead to improved efficiencies for bioreactor harvesting operations such as microfiltration. Experimental studies for flocculation of yeast and CHO cells using cationic polyelectrolytes suggest the existence of a steady-state, self-similar floc size distribution. The experimentally determined floc size distributions were modeled using a population balance approach. For flocculated yeast suspensions, the variation of the floc volume fraction with dimensionless particle diameter is predicted by the population balance model assuming a binary breakage distribution function. However, the variation of floc number fraction with dimensionless particle diameter is better predicted assuming a log normal fragment distribution function probably due to the presence of submicron-sized yeast cell debris. For CHO cell flocs, the floc volume and number fractions are predicted using a log normal fragment distribution function. CHO cells are far more fragile than yeast cells. Thus, individual CHO cells in a CHO cell floc can lyse leading to the formation of a number of small particles. [source] Determination of fluidized bed granulation end point using near-infrared spectroscopy and phenomenological analysisJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2005W. Paul Findlay Abstract Simultaneous real-time monitoring of particle size and moisture content by near-infrared spectroscopy through a window into the bed of a fluidized bed granulator is used to determine the granulation end point. The moisture content and particle size determined by the near-infrared monitor correlates well with off-line moisture content and particle size measurements. The measured particle size is modeled using a population balance approach, and the moisture content is shown to follow accepted models during drying. Given a known formulation, with predefined parameters for peak moisture content, final moisture content, and final granule size, the near-infrared monitoring system can be used to control a fluidized bed granulation by determining when binder addition should be stopped and when drying of the granules is complete. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:604,612, 2005 [source] Copolymer Sequence Distributions in Controlled Radical PolymerizationMACROMOLECULAR REACTION ENGINEERING, Issue 2-3 2009Amin Zargar Abstract Although simulations of polymerizations have been performed using population-balance and method-of-moments techniques to determine the properties of copolymers, the method used most often to estimate copolymer composition distribution is based on probabilistic arguments and is not entirely compatible with the population balance approach. In this paper, a model based on the method of moments is presented that determines not only the molecular weight and copolymer composition characteristics, but also allows prediction of the copolymer distribution. The method is applied to controlled-radical polymerization. Batch polymerizations are simulated to illustrate the effect of composition drift, and shot polymerizations are simulated to show the potential to produce copolymers with customized sequence distributions. [source] Prediction of the Bivariate Molecular Weight-Long Chain Branching Distribution in High-Pressure Low-Density Polyethylene AutoclavesMACROMOLECULAR THEORY AND SIMULATIONS, Issue 6 2007Apostolos Krallis Abstract In the present study a population balance approach is described to follow the time evolution of bivariate molecular weight-long chain branching (MW-LCB) distributions in high pressure low density polyethylene autoclaves. The model formulation is based on a sectional grid method, the so-called fixed pivot technique (FPT). According to this method, the ,live' and ,dead' polymer chain populations are assigned to a selected number of discrete points. Then, the resulting dynamic discrete-continuous molar species equations for ,live' and ,dead' polymer chains are solved at the specified grid points. It is shown that a very good agreement exists between theoretical results and experimental data which proves the capability of the FPT method in calculating the joint MW-LCB distribution for branched polymers. [source] | |||||||||||||