Mantle dynamics and geoid Green functions

cited By 45International audienceWe compute Green functions relating mantle mass heterogeneities to geoid undulations using both incompressible and radially compressible mantle rheologies. Our results differ from those previously published by Forte & Peltier (1991) and Thoraval, Machetel & Cazenave (1994). This is due to two factors. Instead of taking gravity as constant throughout the mantle, we compute it self-consistently with the radial density profile. Secondly, we show that in the mathematical formulation of the compressible case, stresses are not continuous through a density jump. We then point out that the presence of a surface ocean has no additional effect on the geoid signal associated with internal mantle mass anomalies. We apply this formalism to a geodynamic model of mantle density variations and show that an excellent fit to the observed geoid can be obtained. Copyright © 1995, Wiley Blackwell. All rights reserve

Converting mantle tomography into mass anomalies to predict the Earth's radial viscosity

cited By 43In this study, several mantle tomography models are used as input to constrain the amplitude of mass anomalies and viscosity variations with depth in the mantle. For this purpose, we compute the dynamical state of an incompressible mantle overlaid with rigid plates. The best profiles for the viscosity and for the seismic velocity (υ) to density (ρ) conversion factor, ∂ρ/∂υ, are obtained through a Tarantola-Valette inversion by matching the predicted and observed geoid and the poloidal and toroidal surface velocities, and by minimizing the dynamical topography induced by the lower mantle. The recently available second generation of tomography models yields the best results, i.e. 70% of variance reduction for the geoid. An unusual trend of ∂ρ/∂υ with depth is found in the lower mantle. We show that the inversion is more dependent on a priori parameters than on the model, and that there is a strong trade-off between ∂ρ/∂υ and viscosity structures in this kind of modeling. Finally, we discuss the origin of deep mass anomalies in terms of past subduction. © 1994

OPTIMIZATION OF FERMENTATION PLANTS

Techniques for estimation of investment and manufacturing costs in fermentation are discussed. A method for optimization of fermentation Plants as whole is described. 5 It necessitates knowledge of a model of the biosynthesis and equations correlating investment and manufacturing costs to the size of equipment. The Minimization of the non-linear objective function in a non-convex field is obtained by a two step method. Optimization in fermentation industry may have numerous aspects. One may envision improving the growth rate, the production rate or the yield in compound biosynthesis. In this case, the main control parameters are : substrate concentrations, temperature, pH, aeration and agitation etc... Since a mathematical model of microbial cell-growth has been formulated by Monod (1), the kinetic pattern of various fermentation systems has been intensively studied. The number of publications in this field is strongly increasing (2,3,4,5,6). The problem concerning the reduction of manufacturing costs such as those of steam, energy of agitation and aeration, consumption of air, water and raw materials belong to another category of optimization. Okabe and Aiba have recently presented solutions to these problems (7,8,9,10,11). The purpose of this paper concerns the approach of a global optimization of a new plan supposing that the annual production of a fermentation product is given, then the optimization consists in determining the size of the fermentor, power of agitation and aeration system, size of heat exchangers, pumps, filters, centrifuges etc... the required condition for temperature, pH, dissolved oxygen, substrate concentration etc... so that the investment capital and annual expenditure for the production be minimized. Since the same control variables and equipment are used in most fermentation industries, we consider that the method proposed, as regards yeast production, will also apply to various other production

Regulation of branched-chain amino acid biosynthesis by alpha-acetolactate decarboxylase in Streptococcus thermophilus

Aims: To demonstrate the presence of an active alpha-acetolactate decarboxylase in Streptococcus thermophilus and to investigate its physiological function. Methods and Results: Streptococcus thermophilus CNRZ385 contains a gene encoding an alpha-acetolactate decarboxylase. Comparison of the production of alpha-acetolactate and its decarboxylation products, by the parent strain and an alpha-acetolactate decarboxylase-deficient mutant, demonstrated the presence of a control of the pool of alpha-acetolactate by valine, leucine and isoleucine. This control occurs via an allosteric activation of the alpha-acetolactate decarboxylase. Cell-free extracts of S. thermophilus were not able to decarboxylate the isoleucine precursor alpha-acetohydroxybutyrate. Conclusions: These results strongly suggest that one of the physiological functions of the alpha-acetolactate decarboxylase in S. thermophilus is to regulate leucine and valine biosynthesis by diverting the flux of alpha-acetolactate towards acetoin when the branched-chain amino acids are present at a high concentration. Significance and Impact of the Study: Regulation of branched-chain amino acid biosynthesis by alpha-acetolactate decarboxylase may occur in several other micro-organisms and explain some of their growth properties

Une approche symbolique floue pour estimer l'état sensoriel des produits alimentaires : application à l'affinage de fromages

In the food industries, end-products must conform to a compromise between several properties. Among these, the sensory properties are essential because they condition the choice and preferences of consumers. In this problematic, we propose to integrate the operator skill using a fuzzy symbolic approach. Indeed operators play an important role and their knowledge is not given sufficient recognition. More precisely, the aim of our study is to present an application of such an approach to the development of a support system dedicated to help the operator at line in his/her evaluation of the degree of cheese ripening. The results are relevant regarding the objective of control of the sensory properties of the products at the fabrication stage. Thus, the model give the ability to follow the sensory trajectory of the cheese during ripening and help the operator to diagnosis a derive of it in 95 % of the 85 data tested. It opens an interesting road of cooperation between operators and food process control systems.Dans les procédés alimentaires, les produits doivent répondre à un compromis entre plusieurs propriétés. Parmi elles-ci, les propriétés sensorielles sont essentielles car elles conditionnent le choix et les préférences des consommateurs. Dans ce contexte, nous proposons d'intégrer la dimension opérateur dans un système d'aide à la décision en utilisant une approche symbolique floue. L'application traitée est l'affinage de fromages. Les résultats obtenus sont pertinents au regard de l'objectif d'une meilleure maîtrise des propriétés sensorielles en cours de fabrication. Ainsi l'approche développée permet de suivre la trajectoire sensorielle du fromage en cours d'affinage et aide l'opérateur à diagnostiquer de manière prédictive une dérive du produit dans 95% des 85 données testées. Ces résultats ouvrent une voie de coopération intéressante entre les opérateurs et les systèmes d'aide à la décision ou contrôle développés pour les industries alimentaires