Analyse factorielle | EPFL Graph Search

L'analyse factorielle est un terme qui désigne aujourd'hui plusieurs méthodes d'analyses de grands tableaux rectangulaires de données, visant à déterminer et à hiérarchiser des facteurs corrélés aux données placées en colonnes. Au sens anglo-saxon du terme, l'analyse factorielle (factor analysis) désigne une méthode de la famille de la statistique multivariée, utilisée pour décrire un ensemble de variables observées, au moyen de variables latentes (non observées). Pour réduire le nombre de variables, la méthode calcule ces variables latentes comme combinaisons linéaires des variables observées. Créée au début du par Charles Spearman, cette méthode est utilisée en psychologie et particulièrement en psychométrie. Dans la méthodologie Q, Stephenson, un élève de Spearman, distingue l'analyse factorielle R, orientée sur les différences interindividuelles, et l'analyse factorielle Q, orientée sur les différences intraindividuelles . En France, la terminologie « analyse factorielle » repré

THERMAL STORAGE AIMING AT INCREASING THE SHARE OF USED HEAT REJECTED FROM A COOLING PROCESS

Antoine Girardin

Neighbourhood energy concepts for mixed industrial and commercial sites can be developed by applying energy integration techniques. This study presents an application of these techniques on a concrete site (RTA facility in Vienna, Austria), focussing on the possibility to recover the heat rejected from an industrial cooling process to heat a number of office buildings. The data set provided allows for characteristing the heat rejected and modelling the heat recovery possibilities by the help of composite curves. The data characterising the waste heat and the heat demand represented by these curves is generated by a Montecarlo simulation at a hourly time step. The parameters characterising the size of heat recovery and storage equipment are the decision variables of a thermoeconomic objective function which is minimized towards minimal energy costs for the buildings. This analysis leads to the optimal design of heat exchanger and thermal storage. The results show that 35% of the energy costs of a passive building can be saved under such conditions. However, the investments are not profitable for a conventional office building which requires heat at a higher temperature level. This study therefore introduces the need for a further analysis which would take into account the refrigeration requirements on the industrial side and propose an energy system design while taking into account the energy costs of the entire site (office buildings and industrial facility).

2012

Mécanismes d'action du TiO2 illuminé sur Escherichia Coli

Gaëtan Gogniat

The increase of bacterial resistance against various disinfection processes is a worrying phenomenon. As a consequence, the search for alternative techniques for fighting micro-organisms has become one of the major issues of these last few years. In this domain, water treatment is an important preoccupation for many states, either to guarantee the quality of drinking water supply or to detoxify industrial effluents, charged with chemically or biologically pollutants. The financing of this thesis project was provided by the European project AQUACAT. This project aims at evaluating an emerging technology, the titanium dioxide (TiO2) photocatalysis, as an alternative to the traditional water treatments. This technique is based on the illumination of the catalyst, which thus generates reactive oxygen species (ROS), particularly hydroxyls radicals. TiO2 photocatalysis can be used as a water treatment by detoxifying organic compounds and inactivate micro-organisms. Moreover, its bactericidal activity have a promising biomedical future, by killing cancerous cells for example. Although the bactericidal action of the TiO2 photocatalysis is well documented, its mode of action on bacteria was not yet well defined. The objective of this thesis is to contribute to a better comprehension of the mode of action of the TiO2 photocatalysis on the bacterium Escherichia coli. Few microbiologists ever worked on this subject. A review of published articles on the mode of action of TiO2 photocatalysis showed some experimental failures. Moreover, dogmas related to TiO2 photocatalysis showed contradictions, which will be discussed in this thesis. This thesis is divided in four chapters, including two major sections: i) interaction between TiO2 particles, bacteria, biomolecules and salts and ii) the defence mechanisms of the bacterial cells against TiO2 photocatalysis. The first chapter shows that bacterial cells are adsorbed onto TiO2 particles. So as to demonstrate this feature, bacterial cells and TiO2 particles were mix in the presence of two salts affecting at different degrees the effectiveness of TiO2 photocatalysis rate. In the presence of NaCl-KCl, photocatalysis was very effective and the cultivability of the cells decreased at the beginning of the illumination phase. On the contrary, in a phosphate solution, a latency phase of 20 minutes was observed. Using flow cytometry and microscopic observations, we observed very distinctly that the bactericidal effect begun when the cells started to be adsorbed on TiO2 particles. Bacterial adsorption on TiO2 particles could be correlated to the loss of cell cultivability and also to the loss of membrane integrity, measured by flow cytometry. We then studied the interaction between biomolecules (proteins and DNA), bacterial cells and TiO2 particles. Biomolecules strongly adsorbed onto TiO2 particles in a NaCl-KCl solution (up to 60 µg protein per ml of catalyst). A desorption buffer composed of phosphate (50mM, pH 7.0) and SDS (0.1%) is able to desorb 12% only of the proteins. When bacterial cells were in presence of a cell crude extract corresponding to the quantity of proteins belonging to their population (equal to 12µg protein/ml for 2×107 bacteria /ml), it was observed that the effectiveness of the treatment was decreased, suggesting that cell crude extract protected bacterial cells from the photocatalytical treatment. So as to improve our understanding of the mode of action of the TiO2 on the bacterial cells, we compared the survival of E. coli mutants with the wild type one. Knowing that TiO2 generated ROS, we assayed mutant affected in their defence mechanisms against these molecules. Thus, the sensitivity of mutants defected in the induction of DNA repair and of DNA protection systems suggested the induction of cytoplasmic damage by the photocatalytical process. We could also highlight the importance of the Fenton reaction and the formation of hydroxyls radicals in this inactivation process. The hypothesis is that these hydroxyl radicals were also produced in the cells, following an increase in reactive iron and hydrogen peroxide. Interestingly, the loss of E. coli cultivability after TiO2 illumination appeared not only during the illumination, but also when cells were incubate on Petri plates, whereas TiO2 was not illuminated. Thus bacteria underwent a secondary stress, leading also to their loss of cultivability. Finally, we identified genes expressed in the response to the treatment (primary stress) and after a short incubation in a rich culture medium to 37 °C (secondary stress). Thus after an illumination time (100% of bacteria were cultivable) and an other one which show first signs of letality (80% of the cultivable bacteria), no difference in expression of the mRNA could be observed with the transcriptome analysis (DNA chips) of the E. coli genome. On the other hand, as soon as the cell were resuspended in a rich medium after the treatment during only 5 minutes, we could observe differences, by a factor higher than two, in the induction of certain genes. The totality of genes induced during the TiO2 photocatalysis were repressed by Fur and were implied in the iron transport.

EPFL2006

Optimalisation des formes d'organisation dans l'industrie de la construction

Philippe Pot

A piece of work carried out by the construction industry, whether a building or a civil engineering project, is not a mass-produced item. It is always a unique piece of work, by dint of its response to the specific needs of the owner and its potential users, its integration or otherwise into a built environment, and its construction on ground whose geo-technical properties are always specific. This unique piece of work, carried out outside on a site subject to numerous hazards, must nevertheless meet the programme's fixed objectives first time round. Unfortunately, unlike most industrial products, it is usually, even nowadays, the outcome of a fragmented approach: designers and builders of the shell of the building and those engaged in the finishings are in fact involved in a segmented and sequential process, without any real interaction between the various disciplines, to the detriment of overall quality and the cost of the end-product. The author of this thesis has had the opportunity, in his professional career in the management of major construction companies, of testing most organisational forms in the sector. He has observed that, depending on the model chosen, they exercise a more or less beneficial effect on quality, costs and time-frames for completing the works, as well as on the capacity for innovation of the participants themselves. The first objective of the thesis was to analyse the strengths and weaknesses of the most common organisational models in the construction industry and to identify factors in the success of the construction process. The second objective was to suggest an original organisational model which would make optimum use of these factors, taking into account modern organisational theory and project management. The first section of the thesis is an historical study of organisational forms of construction from antiquity to the modern times, and examines in particular the relationships between those actively and directly involved (owner, designers and builders) and their relationships in turn with those involved indirectly (users, public administration, finance providers, environmental and heritage protection organisations, laws and standards, etc.). This historical perspective makes a useful contribution because, although much has been written on architecture and architects, especially the most famous among them, and sometimes on engineers, work looking systematically at the organisational forms used in the construction industry over the centuries is rare. This study demonstrates that the fragmented organisation of construction characteristic of the 20th century is merely an accident in the long history of construction; the twenty-five preceding centuries almost always favoured close collaboration between designers and builders and the wonderful works they left behind demonstrate the wisdom of this approach. Study of the history also provides us with a list of the main success factors and the demands to which the successful organisation of construction must respond. The second part endeavours to verify the relevance of the needs drawn, in the light of modern organisational theory, from project management and creativity, and to complete the list. It goes on to analyse on that basis the strengths and weaknesses of the organisational models most commonly used in the modern construction industry and demonstrates that organisation as a design and build, is in the best position at this stage in the research to meet the needs of owners. The third section verifies, through case studies of five pieces of work recently completed or under construction, whether this organisational model effectively satisfies the expectations of those involved in the construction project, simultaneously examining potential improvements. To that end, a series of interviews was conducted in each case study, with a view to eliciting the views of representative participants: owner, operator, user, project manager, architect, engineer and sub-contracting trades. The process was completed with an analysis of the attitude of some public sector owners to the design and build organisational model. Finally, the lessons drawn from these case studies were used to complete the list of success factors already identified. A final section sets out an original organisational model named Integrated Construction Management (ICM), which recommends an inter-disciplinary approach to construction and responds to the success factors identified in the first three sections. It involves a new division of the production process, which provides the owner with a broader and more cost-effective range of innovative architectural and construction options. It also delivers a series of practical recommendations to assist in the application of the proposed model. In conclusion, Integrated Construction Management places the owner at the centre of a transparent and progressive production process, simultaneously removing the majority of the risks involved in construction. Through its inter-disciplinary approach, it offers innovative solutions together with improvements to the overall quality of the piece of work itself on favourable economic terms. Finally, it enables the owner to take informed decisions and to use his or her financial resources as and when the feasibility of the project is confirmed. It is hoped that, as a result, these advantages will be demonstrated through pilot projects carried out using the ICM model, which will without doubt make possible further improvements in performance.

EPFL2005