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Multiple Steady States (multiple + steady_states)
Selected AbstractsCybernetic Modeling and Regulation of Metabolic Pathways in Multiple Steady States of Hybridoma CellsBIOTECHNOLOGY PROGRESS, Issue 5 2000Maria Jesus Guardia Hybridoma cells utilize a pair of complementary and partially substitutable substrates, glucose and glutamine, for growth. It has been shown that cellular metabolism shifts under different culture conditions. When those cultures at different metabolic states are switched to a continuous mode, they reach different steady states under the same operating conditions. A cybernetic model was constructed to describe the complementary and partial substitutable nature of substrate utilization. The model successfully predicted the metabolic shift and multiple steady-state behavior. The results are consistent with the experimental observation that the history of the culture affects the resulting steady state. [source] Multiple steady states in distillation: Effect of VL(L)E inaccuraciesAICHE JOURNAL, Issue 5 2000Nikolaos Bekiaris Output multiplicities in heterogeneous azeotropic distillation columns were studied. The accuracy of the thermodynamic description is a key factor that determines if multiplicities can be observed in numerical simulations. The descriptions used in the multiplicity-related literature are analyzed. The ,/, analysis of Bekiaris et al. (1996) was used to check implications of inaccuracies in the reported thermodynamics on the existence of multiplicities in azeotropic distillation. On this basis, guidelines are derived concerning what features of thermodynamic descriptions need special attention for use in multiplicity prediction and simulation. Secondly, numerical studies on output multiplicities in heterogeneous azeotropic distillation in the literature were compared to the ,/, predictions wherever possible. The ,/, analysis was used to derive the relations between the reported multiplicities and to identify the physical phenomena causing them. [source] Fan the flame with water: Current ignition, front propagation and multiple steady states in polymer electrolyte membrane fuel cellsAICHE JOURNAL, Issue 12 2009Jay Benziger First page of article [source] HARVESTING AN AGE-STRUCTURED POPULATION AS BIOMASS: DOES IT WORK?NATURAL RESOURCE MODELING, Issue 4 2008OLLI TAHVONEN Abstract The economics of fisheries is based heavily on describing fish populations by the surplus production model. Both economists and ecologists have different opinions on whether this approach provides an adequate biological basis for economic analysis. This study takes an age-structured population model and shows how, under equilibrium conditions, it determines the surplus production model. The surplus production model is then used to solve an optimal feedback policy for a generic optimal harvesting problem. Next, it is assumed that the fishery manager applies this feedback policy even though the fish population actually evolves according to the age-structured model. This framework is applied to the widow rockfish, Atlantic menhaden, and Pacific halibut fisheries. Population age-structure contains information on future harvest possibilities. The surplus production model neglects this information and may lead to major deviations between the expected and actual outcomes especially under multiple steady states and nonlinearities. [source] Dynamic optimization and Skiba sets in economic examplesOPTIMAL CONTROL APPLICATIONS AND METHODS, Issue 5-6 2001Wolf-Jürgen Beyn Abstract We discuss two optimization problems from economics. The first is a model of optimal investment and the second is a model of resource management. In both cases the time horizon is infinite and the optimal control variables are continuous. Typically, in these optimal control problems multiple steady states and periodic orbits occur. This leads to multiple solutions of the state,costate system each of which relates to a locally optimal strategy but has its own limiting behaviour (stationary or periodic). Initial states that allow different optimal solutions with the same value of the objective function are called Skiba points. The set of Skiba points is of interest, because it provides thresholds for a global change of optimal strategies. We provide a systematic numerical method for calculating locally optimal solutions and Skiba points via boundary value problems. In parametric or higher dimensional systems Skiba curves (or manifolds) appear and we show how to follow them by a continuation process. We apply our method to the models above where Skiba sets consist of points or curves and where optimal solutions have different stationary or periodic asymptotic behaviour. Copyright © 2001 John Wiley & Sons, Ltd. [source] Rich and Poor Countries in Neoclassical Trade and GrowthTHE ECONOMIC JOURNAL, Issue 470 2001Alan V. Deardorff A neoclassical growth model provides an explanation for a ,poverty trap', ,club convergence', or ,twin peaks', in terms of specialisation and international trade. The model has many countries with identical linearly homogeneous technologies for producing three goods using capital and labour. With diverse initial endowments, initial equilibrium has unequal factor prices and two diversification cones. With savings out of wages, following Galor (1996), there may easily be multiple steady states. Poor countries converge to a low steady state while rich countries converge to a high one, even though all share identical technological and behavioural parameters. [source] Complex responses to culture conditions in Pseudomonas syringae pv. tomato DC3000 continuous cultures: The role of iron in cell growth and virulence factor inductionBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2010Beum Jun Kim Abstract The growth of a model plant pathogen, Pseudomonas syringae pv. tomato DC3000, was investigated using a chemostat culture system to examine environmentally regulated responses. Using minimal medium with iron as the limiting nutrient, four different types of responses were obtained in a customized continuous culture system: (1) stable steady state, (2) damped oscillation, (3) normal washout due to high dilution rates exceeding the maximum growth rate, and (4) washout at low dilution rates due to negative growth rates. The type of response was determined by a combination of initial cell mass and dilution rate. Stable steady states were obtained with dilution rates ranging from 0.059 to 0.086,h,1 with an initial cell mass of less than 0.6,OD600. Damped oscillations and negative growth rates are unusual observations for bacterial systems. We have observed these responses at values of initial cell mass of 0.9,OD600 or higher, or at low dilution rates (<0.05,h,1) irrespectively of initial cell mass. This response suggests complex dynamics including the possibility of multiple steady states. Iron, which was reported earlier as a growth limiting nutrient in a widely used minimal medium, enhances both growth and virulence factor induction in iron-supplemented cultures compared to unsupplemented controls. Intracellular iron concentration is correlated to the early induction (6,h) of virulence factors in both batch and chemostat cultures. A reduction in aconitase activity (a TCA cycle enzyme) and ATP levels in iron-limited chemostat cultures was observed compared to iron-supplemented chemostat cultures, indicating that iron affects central metabolic pathways. We conclude that DC3000 cultures are particularly dependent on the environment and iron is likely a key nutrient in determining physiology. Biotechnol. Bioeng. 2010;105: 955,964. © 2009 Wiley Periodicals, Inc. [source] On extremum seeking in bioprocesses with multivalued cost functionsBIOTECHNOLOGY PROGRESS, Issue 3 2009Georges Bastin Abstract Finding optimal operating modes for bioprocesses has been, for a long time, a relevant issue in bioengineering. The problem is of special interest when it implies the simultaneous optimization of competing objectives. In this paper, we address the problem of finding optimal steady states that achieve the best tradeoff between yield and productivity by using nonmodel - based extremum-seeking control with semiglobal practical stability and convergence properties. A special attention is paid to processes with multiple steady states and multivalued cost functions. © 2009 American Institute of Chemical Engineers Biotechnol. 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