Browsing by Author "Perez Correa, R"

Now showing 1 - 9 of 9
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    A neural network estimator for total biomass of filamentous fungi growing on two dimensional solid substrate
    (KLUWER ACADEMIC PUBL, 1998) Acuna, G; Giral, R; Agosin, E; Jorquera, H; Perez Correa, R; Ferret, E; Molin, P; Thibault, J
    A neural network dynamic model is proposed for the on-line estimation of total biomass during filamentous fungi cultures on two dimensional solid substrate. The neural network provides an accurate and robust estimation of biomass from macroscopic measurements of the colony radius evolution. Experiments were performed on Gibberella fujikuroi growing on Petri dishes under different conditions of temperature and water activity.
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    Comparison of experimental methods for measuring infinite dilution volatilities of aroma compounds in water/ethanol mixtures
    (AMER CHEMICAL SOC, 2004) Athes, V; Lillo, MPY; Bernard, C; Perez Correa, R; Souchon, I
    Several experimental methodologies exist for measuring volatilities; however, results show great dispersion and sometimes lack of agreement between different methods. The aim of our study was to compare the performance of three static headspace methods (vapor phase calibration, VPC; phase ratio variation, PRV; and liquid calibration static headspace, LC-SH) for determining gas/liquid partition coefficients of two aroma compounds in hydroalcoholic multicomponent solutions at infinite dilution. Comparison with literature data based on static and dynamic methods showed that PRV is simpler than VPC and LC-SH and that VPC and PRV are more accurate than LC-SH, which presented a significant bias (50% lower values).
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    Dynamic modelling and advanced multivariable control of conventional flotation circuits
    (PERGAMON-ELSEVIER SCIENCE LTD, 1998) Perez Correa, R; Gonzalez, G; Casali, A; Cipriano, A; Barrera, R; Zavala, E
    Expert and predictive multivariable control algorithms for a conventional cooper flotation circuit were assessed through simulations These simulations were carried out with a nonlinear dynamic model, derived from mass balances and empirical relationships, that qualitatively reproduced the dynamic behaviour of a real plant well. In order to make the simulations more realistic, they included noisy measurements, stochastic parameter variations and input disturbances. New expert algorithms were able to keep the plant operating within a pre-defined zone for long periods without complete control saturation, unlike previous expert controllers. In addition, the inclusion of constraints in a multivariable predictive algorithm verified improved control system regulation and flexibility. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
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    Indirect measurement of water content in an aseptic solid substrate cultivation pilot-scale bioreactor
    (JOHN WILEY & SONS INC, 2001) Lillo, MPY; Perez Correa, R; Agosin, E; Latrille, E
    A lack of models and sensors for describing and monitoring large-scale solid substrate cultivation (SSC) bioreactors has hampered industrial development and application of this type of process. This study presents an indirect dynamic measurement model for a 200-kg-capacity fixed-bed SSC bioreactor under periodic agitation. Growth of the filamentous fungus Gibberella fujikuroi on wheat bran was used as a case study. Real data were preprocessed using previously reported methodology. The model uses CO, production rate and inlet air conditions to estimate average bed water content and average bed temperature. The model adequately reproduces the evolution of the average bed water content and can therefore be used as an on-line estimator in pilot-scale SSC bioreactors. To obtain a reasonable fit of the bed temperature, however, inlet air humidity measurements will have to be adjusted with a data reconciliation algorithm. Good estimation of temperature is important for the future design of improved water content estimation using state observers. The model also provides insight into understanding the complex behavior of the dynamic system, which could prove useful when establishing advanced model-based operational and control strategies. (C) 2001 John Wiley & Sons, Inc.
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    Modelling Gibberella fujikuroi growth and GA(3) production in solid-state fermentation
    (ELSEVIER SCI LTD, 2002) Gelmi, C; Perez Correa, R; Agosin, E
    A simple differential equation model was developed to represent the growth and production of a secondary metabolite in solid-state cultivation (SSC) under conditions of limited nitrogen. The model was used to interpret data obtained from SSCs of the fungus Gibberella fujikuroi, under different temperatures (25 and 31 degreesC) and water activity conditions (0.985, 0.992, 0.999). The model was calibrated in two steps. An innovative procedure to achieve good initial guesses for key parameters, such as maintenance coefficients and death rates was first applied. These initial guesses were then used in a non-linear optimisation routine to get a minimum least squares fit for the model. The mathematical model was able to reproduce the measured variables: biomass, urea, starch, CO2, O-2 and GA(3) satisfactorily. Moreover. the model indicated that the fungus does not assimilate the nitrogen source, urea, directly. The model will be useful in developing optimal feeding policies and on-line biomass estimators. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.
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    Reassessment of the estimation of dissolved oxygen concentration profile and K(L)a in solid-state fermentation
    (ELSEVIER SCI LTD, 2000) Thibault, J; Pouliot, K; Agosin, E; Perez Correa, R
    Oxygen mass transfer in aerobic microbial growth systems is often a limiting factor for optimal growth and productivity. Oxygen mass transfer has been widely studied in submerged fermentations but has attracted as yet little attention for solid state fermentations. The parallel to submerged fermentation has led to the incorrect interpretation and use of the overall oxygen mass transfer coefficient (K(L)a) to assess the ability of a particular fermentation system to supply the oxygen to microorganisms. The use of K(L)a, as traditionally defined, should be used with caution in solid substrate fermentation systems because there is no convection on the liquid side of the medium, and oxygen is consumed in the biofilm. Hence, K(L)a must be redefined for solid state fermentation. In this payer, the use of oxygen mass transfer coefficients in solid state fermentations is clarified. Published literature data were analysed with a simple pseudo-steady-state model and used to discuss the influence of the biofilm thickness, the dissolved oxygen diffusion coefficient, the convective gas mass transfer coefficient, and the gas flow rate on the oxygen mass transfer coefficient in solid state fermentations. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.
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    Rigorous dynamic modeling and simulation of wine distillations
    (ELSEVIER SCI LTD, 2004) Osorio, D; Perez Correa, R; Belancic, A; Agosin, E
    A novel simulation strategy for dynamic distillation of complex mixtures, such as wine, is proposed and evaluated in terms of computing efficiency and accuracy. The model developed describes wine distillation as a multicomponent reactive batch distillation process. The simulation approach transforms the system of differential algebraic equations (DAE) into a set of ordinary differential equations, by pre-solving the algebraic equations and replacing them with artificial neural networks.
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    Solid substrate cultivation of Gibberella fujikuroi on an inert support
    (ELSEVIER SCI LTD, 2000) Gelmi, C; Perez Correa, R; Gonzalez, M; Agosin, E
    Growth of Gibberella fujikuroi on Amberlite, an inert support, and gibberellic acid (GA,) production was studied in glass columns under different conditions of temperature and water activity (a(w)). Maximum biomass concentration and GA(3) production were respectively 40 (mg/g inert support) and 0.73 (mg/g inert support). While high specific growth rates were obtained, low initial nitrogen resulted in low biomass concentrations. Maximum GA(3) (31 degrees C, a(w)=0.985) was not produced by the maximum concentration of biomass (25 degrees C, a(w)=0.992). Peaks in the rate curves of either outlet gas, CO2 or O-2 occurred on exhaustion of urea indicating, for future works, just when to feed the culture additional nitrogen. (C) 2000 Elsevier Science Ltd. All rights reserved.
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    Solid substrate fermentation of Monascus purpureus: Growth, carbon balance, and consistency analysis
    (WILEY, 2000) Rosenblitt, A; Agosin, E; Delgado, J; Perez Correa, R
    Solid substrate fermentation (SSF) of Monascus purpureus on rice is a promising new technology for obtaining natural pigments. However, before attempts can be made at maximizing pigment yield, all significant macroscopic compounds should be assayed. Here, Monascus purpureus has been grown on rice in batch mode, and the evolution of the main components, biomass, residual rice, O-2, CO2, ethanol, acetic acid, and pigments, have been followed. This set of data, never previously studied for Monascus SSF, allowed both the performance of a macroscopic elemental balance, which accounted for 83-94% of the initial substrate carbon, and a check of data consistency. Standard consistency analysis showed a significant underestimation of the nitrogen fraction of biomass, but it was unable to discriminate the errors in the carbon balance as a result of the simultaneous presence of two gross errors in the system. A simple stoichiometric model in tandem with consistency analysis explained unaccounted carbon as an underestimation of CO2 and ethanol. Using the simplified method to estimate ethanol, the macroscopic balance accounted for 87-99% of the initial carbon.