Use of genetic algorithms and gradient based optimization techniques for calcium phosphate precipitation

Phase equilibrium computations constitute an important problem for designing and optimizing crystallization processes. The Gibbs free energy is generally used as an objective function to find phase amount and composition at equilibrium. In such problems, the Gibbs free energy may be a quite complex function, with several local minima. This paper presents a contribution to handle this kind of problems by implementation of an optimization technique based on the successive use of a genetic algorithm (GA) and of a classical sequential quadratic programming (SQP) method: the GA is used to perform a preliminary search in the solution space for locating the neighborhood of the solution. Then, the SQP method is employed to refine the best solution provided by the GA. The basic operations involved in the design of the GA developed in this study (encoding with binary representation of real values, evaluation function, adaptive plan) are presented. Several test problems are first presented to demonstrate the validity of the approach. Then, calcium phosphate precipitation which is of major interest for P-recovery from wastewater, has been chosen as an illustration of the implemented algorithm

Modeling and Optimization of Lactic Acid Synthesis by the Alkaline Degradation of Fructose in a Batch Reactor

The present work deals with the determination of the optimal operating conditions of lactic acid synthesis by the alkaline degradation of fructose. It is a complex transformation for which detailed knowledge is not available. It is carried out in a batch or semi-batch reactor. The ‘‘Tendency Modeling’’ approach, which consists of the development of an approximate stoichiometric and kinetic model, has been used. An experimental planning method has been utilized as the database for model development. The application of the experimental planning methodology allows comparison between the experimental and model response. The model is then used in an optimization procedure to compute the optimal process. The optimal control problem is converted into a nonlinear programming problem solved using the sequencial quadratic programming procedure coupled with the golden search method. The strategy developed allows simultaneously optimizing the different variables, which may be constrained. The validity of the methodology is illustrated by the determination of the optimal operating conditions of lactic acid production

Constraint handling strategies in Genetic Algorithms application to optimal batch plant design

Optimal batch plant design is a recurrent issue in Process Engineering, which can be formulated as a Mixed Integer Non-Linear Programming(MINLP) optimisation problem involving specific constraints, which can be, typically, the respect of a time horizon for the synthesis of various products. Genetic Algorithms constitute a common option for the solution of these problems, but their basic operating mode is not always wellsuited to any kind of constraint treatment: if those cannot be integrated in variable encoding or accounted for through adapted genetic operators, their handling turns to be a thorny issue. The point of this study is thus to test a few constraint handling techniques on a mid-size example in order to determine which one is the best fitted, in the framework of one particular problem formulation. The investigated methods are the elimination of infeasible individuals, the use of a penalty term added in the minimized criterion, the relaxation of the discrete variables upper bounds, dominancebased tournaments and, finally, a multiobjective strategy. The numerical computations, analysed in terms of result quality and of computational time, show the superiority of elimination technique for the former criterion only when the latter one does not become a bottleneck. Besides, when the problem complexity makes the random location of feasible space too difficult, a single tournament technique proves to be the most efficient one

Applicability and generalisability of the results of systematic reviews to public health practice and policy: a systematic review

<p>Abstract</p> <p>Background</p> <p>The purpose of the study was to evaluate systematic reviews of research into two public health priorities, tobacco consumption and HIV infection, in terms of the reporting of data related to the applicability of trial results (i.e., whether the results of a trial can be reasonably applied or generalized to a definable group of patients in a particular setting in routine practice, also called external validity or generalisability).</p> <p>Methods</p> <p>All systematic reviews of interventions aimed at reducing or stopping tobacco use and treating or preventing HIV infection published in the Cochrane database of systematic reviews and in journals indexed in MEDLINE between January 1997 and December 2007 were selected. We used a standardized data abstraction form to extract data related to applicability in terms of the context of the trial, (country, centres, settings), participants (recruitment, inclusion and exclusion criteria, baseline characteristics of participants such as age, sex, ethnicity, coexisting diseases or co-morbidities, and socioeconomic status), treatment (duration, intensity/dose of treatment, timing and delivery format), and the outcomes assessment from selected reviews.</p> <p>Results</p> <p>A total of 98 systematic reviews were selected (57 Cochrane reviews and 41 non-Cochrane reviews); 49 evaluated interventions aimed at reducing or stopping tobacco use and 49 treating or preventing HIV infection. The setting of the individual studies was reported in 45 (46%) of the systematic reviews, the number of centres in 21 (21%), and the country where the trial took place in 62 (63%). Inclusion and exclusion criteria of the included studies were reported in 16 (16%) and 13 (13%) of the reviews, respectively. Baseline characteristics of participants in the included studies were described in 59 (60%) of the reviews. These characteristics concerned age in about half of the reviews, sex in 46 (47%), and ethnicity in 9 (9%).</p> <p>Applicability of results was discussed in 13 (13%) of the systematic reviews. The reporting was better in systematic reviews by the Cochrane Collaboration than by non-Cochrane groups.</p> <p>Conclusions</p> <p>Our study highlighted the lack of consideration of applicability of results in systematic reviews of research into 2 public health priorities: tobacco consumption and HIV infection.</p