Mathematical Methods of Operational Research, Nov 30, 2001
We consider a class of time-varying stochastic control systems, with Borel state and action space... more We consider a class of time-varying stochastic control systems, with Borel state and action spaces, and possibly unbounded costs. The processes evolve according to a discrete-time equation x nþ1 ¼ G n ðx n ; a n ; x n Þ, n ¼ 0; 1; . . . ;
We consider a class of time-varying stochastic control systems, with Borel state and action space... more We consider a class of time-varying stochastic control systems, with Borel state and action spaces, and possibly unbounded costs. The processes evolve according to a discrete-time equation x nþ1 ¼ G n ðx n ; a n ; x n Þ, n ¼ 0; 1; . . . ;
In this paper, two modelling approaches are proposed for wine-making fermentations. The first one... more In this paper, two modelling approaches are proposed for wine-making fermentations. The first one is largely based on the first principle modelling approach and considers the main yeast physiological mechanisms. The model accurately predicts the fermentation kinetics of more than 80% of a large number of experiments performed with 20 wine yeast strains, 69 musts and different fermentation conditions. Thanks to the wide domain of validity of the model, a simulator based on this model coupled to a thermal model was developed to help winemakers to optimize tank management. It predicts the end of the fermentation and changes in the rate of fermentation but furthermore includes an optimization module based on fuzzy logic which allows, via temperature profiles and nitrogen addition strategies, to decrease the duration of fermentation and the energy requirements at winery scale according to user specifications. The objective of the second modelling approach is the development of a mathematical model of the fermentation process including some minority by-products known as characteristic flavour compounds. It refers to metabolic engineering and accounts for the intracellular behaviour of the yeast Saccharomyces cerevisiae by using approaches like the Metabolic Flux Analysis (MFA) and the Elementary Flux Modes (EFMs). A state of the art describes the application of these methods in the restrained field of wine-making/fermentation conditions and underlines the potential of such approaches.
We consider a class of time-varying R d -valued control models, and with possibly unbounded costs... more We consider a class of time-varying R d -valued control models, and with possibly unbounded costs. The processes evolve according to the system equation xn+1 = Gn(xn; an) + n (n ∈ N), where { n} are i.i.d. random vectors and {Gn} a sequence of known functions converging to some function G∞. Under suitable hypotheses, we show the existence of an -discount optimal policy for the limiting system xn+1 = G∞(xn; an) + n.
Journal of the American Society For Horticultural Science, Mar 1, 2008
Whereas quality is an increasingly important aspect of peach fruit [Prunus persica (L.) Batsch] p... more Whereas quality is an increasingly important aspect of peach fruit [Prunus persica (L.) Batsch] production at this time, it is still not adequately addressed in crop models. Our objective was to develop a model to assess an essential trait of peach fruit quality (the refractometric index at harvest) to include it in existing crop models and to address the issue of quality in programs dealing with the improvement of crop management. The model predicts the fruit refractometric index, an indicator of sugar content (the most decisive parameter in consumer satisfaction) commonly used by the fruit industry. The model was simple enough so that it could be easily linked to carbon-based crop models. It was calibrated and tested using several independent data sets representing many growing conditions. To account for the effect of uncertainty in input and model parameters, the output of the model was qualified by a prediction interval. Results indicated that the model accurately predicted refractometric indices under 12% (relative root mean squared error values of 0.09 and 0.12 for two data sets), which corresponds to the fruit industry's range of interest. Prediction intervals revealed that the uncertainty in model parameters has moderate effects, whereas the uncertainty of the model input has important effects.
We introduce two novel procedures to test the nullity of the slope function in the functional lin... more We introduce two novel procedures to test the nullity of the slope function in the functional linear model with real output. The test statistics combine multiple testing ideas and random projections of the input data through functional Principal Component Analysis. Interestingly, the procedures are completely datadriven and do not require any prior knowledge on the smoothness of the slope nor on the smoothness of the covariate functions. The levels and powers against local alternatives are assessed in a nonasymptotic setting. This allows us to prove that these procedures are minimax adaptive (up to an unavoidable log log n multiplicative term) to the unknown regularity of the slope. As a side result, the minimax separation distances of the slope are derived for a large range of regularity classes. A numerical study illustrates these theoretical results.
... Document de Travail n°2005-62 IS FISHING COMPATIBLE WITH ENVIRONMENTAL CONSERVATION: A STOCHA... more ... Document de Travail n°2005-62 IS FISHING COMPATIBLE WITH ENVIRONMENTAL CONSERVATION: A STOCHASTIC MODEL WITH AN ELEMENT OF SELF-PROTECTION Dominique AMI Nadine HILGERT Sophie PARDO Mabel TIDBALL December 2005 Page 2. ...
Nitrogen fertilization and winter pruning are commonly used to control crop production in peach [... more Nitrogen fertilization and winter pruning are commonly used to control crop production in peach [Prunus persica (L.) Batsch] orchards. They are also known to affect the dynamics of Myzus persicae (Sulzer) (Homoptera: Aphididae) aphid populations via bottom-up regulation processes. Interactions between crops and pests can cause complex system behaviour in response to management practices. An integrated approach will therefore improve the understanding of the effects of these two cultural practices on aphid and peach performances.
The change in catches and mean size of one-year-old perch (Perca fluviatilis) in Lake Geneva was ... more The change in catches and mean size of one-year-old perch (Perca fluviatilis) in Lake Geneva was studied between 1957 and 2005, and related to trophic changes and average temperature. The status of Lake Geneva, assessed on the basis of total phosphorus concentrations, switched from being oligotrophic before 1960 to eutrophic, with total phosphorus concentration reaching nearly 90 µg L −1 in 1976-1979. In response to management measures, the trophic status then returned to mesotrophy in the early 2000s. Zooplankton is the main food consumed by young perch, and quantities present (annual biovolumes of zooplankton) were recorded throughout the study period. The lake water temperature was also recorded. Data obtained from perch catches and perch spawns enabled eleven strong cohorts of perch to be identified. Strong cohorts dominated the stock for three years, until they were massively caught by fishermen. Yields have fluctuated widely, increasing rapidly until 1975, and subsequently decreasing, with an exceptional decline between 1976 and 1981. During the period 1977-1981, unfavourable climatic conditions in spring were probably the main cause of this fall in perch yields. For the other periods, perch yields and the mean size of one-year-old perch were significantly correlated with trophic parameters, total phosphorus concentration and zooplankton biovolume. Correlations are higher if only strong cohorts are taken into account. As a result of the re-oligotrophication process, perch growth has been progressively reduced, age at first maturity delayed and strong cohorts become less frequent; the mean size of 0+ individuals in strong cohorts is significantly smaller than in the other cohorts, suggesting a population density effect in the context of a limited supply of zooplankton. During the study period, trophic changes in Lake Geneva have had more impact on perch growth and yield than has temperature, since no significant correlation could be detected between water temperature and perch growth.
Mathematical Methods of Operational Research, Nov 30, 2001
We consider a class of time-varying stochastic control systems, with Borel state and action space... more We consider a class of time-varying stochastic control systems, with Borel state and action spaces, and possibly unbounded costs. The processes evolve according to a discrete-time equation x nþ1 ¼ G n ðx n ; a n ; x n Þ, n ¼ 0; 1; . . . ;
We consider a class of time-varying stochastic control systems, with Borel state and action space... more We consider a class of time-varying stochastic control systems, with Borel state and action spaces, and possibly unbounded costs. The processes evolve according to a discrete-time equation x nþ1 ¼ G n ðx n ; a n ; x n Þ, n ¼ 0; 1; . . . ;
In this paper, two modelling approaches are proposed for wine-making fermentations. The first one... more In this paper, two modelling approaches are proposed for wine-making fermentations. The first one is largely based on the first principle modelling approach and considers the main yeast physiological mechanisms. The model accurately predicts the fermentation kinetics of more than 80% of a large number of experiments performed with 20 wine yeast strains, 69 musts and different fermentation conditions. Thanks to the wide domain of validity of the model, a simulator based on this model coupled to a thermal model was developed to help winemakers to optimize tank management. It predicts the end of the fermentation and changes in the rate of fermentation but furthermore includes an optimization module based on fuzzy logic which allows, via temperature profiles and nitrogen addition strategies, to decrease the duration of fermentation and the energy requirements at winery scale according to user specifications. The objective of the second modelling approach is the development of a mathematical model of the fermentation process including some minority by-products known as characteristic flavour compounds. It refers to metabolic engineering and accounts for the intracellular behaviour of the yeast Saccharomyces cerevisiae by using approaches like the Metabolic Flux Analysis (MFA) and the Elementary Flux Modes (EFMs). A state of the art describes the application of these methods in the restrained field of wine-making/fermentation conditions and underlines the potential of such approaches.
We consider a class of time-varying R d -valued control models, and with possibly unbounded costs... more We consider a class of time-varying R d -valued control models, and with possibly unbounded costs. The processes evolve according to the system equation xn+1 = Gn(xn; an) + n (n ∈ N), where { n} are i.i.d. random vectors and {Gn} a sequence of known functions converging to some function G∞. Under suitable hypotheses, we show the existence of an -discount optimal policy for the limiting system xn+1 = G∞(xn; an) + n.
Journal of the American Society For Horticultural Science, Mar 1, 2008
Whereas quality is an increasingly important aspect of peach fruit [Prunus persica (L.) Batsch] p... more Whereas quality is an increasingly important aspect of peach fruit [Prunus persica (L.) Batsch] production at this time, it is still not adequately addressed in crop models. Our objective was to develop a model to assess an essential trait of peach fruit quality (the refractometric index at harvest) to include it in existing crop models and to address the issue of quality in programs dealing with the improvement of crop management. The model predicts the fruit refractometric index, an indicator of sugar content (the most decisive parameter in consumer satisfaction) commonly used by the fruit industry. The model was simple enough so that it could be easily linked to carbon-based crop models. It was calibrated and tested using several independent data sets representing many growing conditions. To account for the effect of uncertainty in input and model parameters, the output of the model was qualified by a prediction interval. Results indicated that the model accurately predicted refractometric indices under 12% (relative root mean squared error values of 0.09 and 0.12 for two data sets), which corresponds to the fruit industry's range of interest. Prediction intervals revealed that the uncertainty in model parameters has moderate effects, whereas the uncertainty of the model input has important effects.
We introduce two novel procedures to test the nullity of the slope function in the functional lin... more We introduce two novel procedures to test the nullity of the slope function in the functional linear model with real output. The test statistics combine multiple testing ideas and random projections of the input data through functional Principal Component Analysis. Interestingly, the procedures are completely datadriven and do not require any prior knowledge on the smoothness of the slope nor on the smoothness of the covariate functions. The levels and powers against local alternatives are assessed in a nonasymptotic setting. This allows us to prove that these procedures are minimax adaptive (up to an unavoidable log log n multiplicative term) to the unknown regularity of the slope. As a side result, the minimax separation distances of the slope are derived for a large range of regularity classes. A numerical study illustrates these theoretical results.
... Document de Travail n°2005-62 IS FISHING COMPATIBLE WITH ENVIRONMENTAL CONSERVATION: A STOCHA... more ... Document de Travail n°2005-62 IS FISHING COMPATIBLE WITH ENVIRONMENTAL CONSERVATION: A STOCHASTIC MODEL WITH AN ELEMENT OF SELF-PROTECTION Dominique AMI Nadine HILGERT Sophie PARDO Mabel TIDBALL December 2005 Page 2. ...
Nitrogen fertilization and winter pruning are commonly used to control crop production in peach [... more Nitrogen fertilization and winter pruning are commonly used to control crop production in peach [Prunus persica (L.) Batsch] orchards. They are also known to affect the dynamics of Myzus persicae (Sulzer) (Homoptera: Aphididae) aphid populations via bottom-up regulation processes. Interactions between crops and pests can cause complex system behaviour in response to management practices. An integrated approach will therefore improve the understanding of the effects of these two cultural practices on aphid and peach performances.
The change in catches and mean size of one-year-old perch (Perca fluviatilis) in Lake Geneva was ... more The change in catches and mean size of one-year-old perch (Perca fluviatilis) in Lake Geneva was studied between 1957 and 2005, and related to trophic changes and average temperature. The status of Lake Geneva, assessed on the basis of total phosphorus concentrations, switched from being oligotrophic before 1960 to eutrophic, with total phosphorus concentration reaching nearly 90 µg L −1 in 1976-1979. In response to management measures, the trophic status then returned to mesotrophy in the early 2000s. Zooplankton is the main food consumed by young perch, and quantities present (annual biovolumes of zooplankton) were recorded throughout the study period. The lake water temperature was also recorded. Data obtained from perch catches and perch spawns enabled eleven strong cohorts of perch to be identified. Strong cohorts dominated the stock for three years, until they were massively caught by fishermen. Yields have fluctuated widely, increasing rapidly until 1975, and subsequently decreasing, with an exceptional decline between 1976 and 1981. During the period 1977-1981, unfavourable climatic conditions in spring were probably the main cause of this fall in perch yields. For the other periods, perch yields and the mean size of one-year-old perch were significantly correlated with trophic parameters, total phosphorus concentration and zooplankton biovolume. Correlations are higher if only strong cohorts are taken into account. As a result of the re-oligotrophication process, perch growth has been progressively reduced, age at first maturity delayed and strong cohorts become less frequent; the mean size of 0+ individuals in strong cohorts is significantly smaller than in the other cohorts, suggesting a population density effect in the context of a limited supply of zooplankton. During the study period, trophic changes in Lake Geneva have had more impact on perch growth and yield than has temperature, since no significant correlation could be detected between water temperature and perch growth.
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