Conceptual model | EPFL Graph Search

A conceptual model is a representation of a system. It consists of concepts used to help people know, understand, or simulate a subject the model represents. In contrast, a physical model focuses on a physical object such as a toy model that may be assembled and made to work like the object it represents. The term may refer to models that are formed after a conceptualization or generalization process. Conceptual models are often abstractions of things in the real world, whether physical or social. Semantic studies are relevant to various stages of concept formation. Semantics is basically about concepts, the meaning that thinking beings give to various elements of their experience. Overview :See digital twin, simulation Models of concepts and models that are conceptual The term conceptual model is normal. It could mean "a model of concept" or it could mean "a model that is conceptual." A distinction can be made between what models are and what models are made

Approche mathématique de l'impact des sites contaminés sur les eaux souterraines dans un contexte d'analyse de risque

Dominique Guyonnet

The primary objectives of this thesis are, firstly, to develop analytical solutions for estimating the impact of contaminated sites (in particular landfills, and to a lesser extent accidentally contaminated soils) on groundwater, and secondly to evaluate methods for taking into account the uncertainty relative to the different relevant parameters. These developments are performed with particular reference to a risk analysis framework. One of the distinctive features of such a framework is the incomplete and uncertain nature of the information that is generally available in practice. This has a direct influence on the choice of tools and approaches. It is proposed, in the introductory chapter, to define risk as the likelihood that a damage may occur, thus avoiding the more frequently used term probability. The latter refers to a strictly statistical description of the uncertainty, and assumes a degree of knowledge with respect to the various relevant parameters that is not necessarily available in practice. A presentation of several risk analysis models underlines their respective areas of application. Chapter 2 presents analytical solutions for estimating the impact of contaminated sites on groundwater, several of which are original. The mathematical development of the original solutions is presented in detail in the appendix. The succession of proposed solutions goes from the simpler to the more complex, starting with solutions for a one-layer domain and one-, two- and three-dimensional contaminant migration, and then passing to solutions for a multi-layer domain. These solutions are presented in terms of dimensionless variables that allow the equations to be written in a compact fashion, and independently of any system of units. The dimensionless variables serve to construct type curves that provide a visual analysis of solution behaviour with respect to variations of input parameter values. The proposed original solutions are of particular interest for estimating the potential impact of waste disposal sites, as they take into account the effect of the diffusive-dispersive flux on the impact on groundwater. This component of the mass flux is generally either omitted by existing risk analysis tools, or else it is not truly coupled with the mass balance in the groundwater (via the boundary conditions). The proposed solutions are applied to several practical examples. The example involving the original solution developed for estimating the impact of a stabilized waste-disposal site, illustrates the solution's usefulness as an aid for site conception and design. The example also shows how, by providing a picture of the site's global performance with respect to its potential impact, the model can bring the designer to question some of his choices. Another example helps to clarify the concept of "equivalence" between different barrier systems. An original solution is also proposed for the problem of early contaminant detection using inorganic trace elements. A comparison with another approach proposed in the literature illustrates the limits of the latter. Chapter 3 addresses the question of how to take imperfection of knowledge into account in the calculations. Two methods for accounting for uncertainty with respect to input parameter values are described and compared. The first method is the Monte Carlo method, which relates to a statistical and probabilistic framework. The second method is based on the theory of possibilities and on so-called fuzzy calculus. The representation of the main model parameters (hydraulic conductivity, porosity, etc.) using fuzzy numbers rather than probability distributions, is often more consistent with the basic nature of the information that is available in practice. The comparison between the two methods, underlines the conservative character of the fuzzy approach. This is related to the fact that the calculation based on fuzzy numbers considers all possible combinations of fuzzy input parameter values, but does not transmit (through multiplication) the degrees of unlikelihood of the different values. In the Monte Carlo calculation, on the other hand, a scenario that combines low-probability values of the input parameters, has all the less chance of being randomly selected. Nevertheless, when the mere possibility that an unfavourable scenario may occur becomes an element of decision, the fuzzy approach may seem preferable. This situation can appear in an environmental context, where human health is often at stake. The examples presented herein contribute to introducing an "impact framework" to the management of contaminated sites. Such a framework tends to define the acceptability of choices with respect to the management of these sites, on the basis of a comparison between emitted pollutant fluxes and fluxes considered acceptable for the local environment. They also underline the usefulness of having a certain degree of freedom with respect to the choice of the conceptual model underlying the mathematical model, in order to provide reasonable appropriateness between the calculation tool and the various situations that might appear in practice. Existing risk analysis models are often difficult to apply to specific sites, due to the rigidity of their conceptual models. In some cases, these models are better described as tools for ranking chemical substances as a function of their contamination potential. Some of the original analytical solutions proposed herein can be readily incorporated into the "vector" module of a risk analysis tool.

EPFL1998

Reverse engineering the motor control system

Berat Denizdurduran

Mammalian motor control is implemented by a combination of different networks and system, working coherently to plan the movement of the body or a limb and to execute this movement a dynamical environment. While it is believed that complex, voluntary movements are planned in the motor areas of the cortex, the execution of the movement is controlled by a combination of cortical and cerebellar networks together with central pattern generators and reflex circuits in the spinal cord. In this thesis, we propose an abstract model that captures the basic properties of mammalian motor control, using the example of two different movements: arm movements as well as locomotion. Our model consists of three parts: first a high-level network, that learns movements, using a combination of actor-critic based reinforcement learning and Optimal Control theory. The second part corresponds to spinal reflex circuits that execute basic movements of the musculo-skeletal system. They are modeled by a simple neural network, that learns the dynamic properties of the muscoloskeletal system by the mechanism of spontaneous motor activity (muscle twithing) combined with a Hebbian learning rule. We demonstrate that this network can learn the antagonistic control of joint movements. The final part of the model is a cerebellar network, that translates a complex movement trajectory, such as reaching, and activates the spinal reflex circuits to execute the movement. The mapping between the cerebellar neurons and the spinal reflex circuits are trained with artificial neural networks. Using a musculoskeletal arm model, we demonstrate that the proposed neural motor control model can generate the movement to arbitrary goal position.

EPFL2019

Alexandre Sarrasin (1895-1976) et l'esthétique de l'ingénieur

Philippe Mivelaz

Alexandre Sarrasin (1895-1976) studied at Zürich Federal Swiss Institute of Technology (ETH) from 1913 to 1918. Despite First World War's conflicts surrounding the neutral Switzerland, the intellectual climate inside ETH was cosmopolitan and liberal. As unique educational institution directly depending from the Federal government, the ETH played an important role in shaping modern Switzerland where country planning and infrastructure building were the central power's main tasks. Engineers were important figures of this process of modernization. They embodied the values of the industrial revolution: rationality, efficiency and the huge power of transformation of the country and its society. Sarrasin opened an engineer's office in Lausanne in 1921 and in Brussell two years later. He established himself in the capital of Belgium in 1927 while ruling at the same time his office in Lausanne. He came back to Switzerland when the German army invaded Belgium. The office in Bruxells was maintained up to the early 1960's. Branches were opened in Sion and Geneva during the 1950's. Sarrasin's work concerned foundations, buildings, bridges and some dams also. Nearly all these constructions works were made of reinforced concrete, his favorite material. This thesis is dedicated to the construction works, especially the bridges in Valais, Sarrasin's native district, and the aesthetic question in engineer's design. Of the bridge of Branson (1924- 1925) near Fully, his first important commission, he wrote that "The elegance of the design is due to its simplicity. The quietness of its lines is fully harmonized with the landscape. Nothing was planned for the decoration. The bridge is the simple realization of a mathematical truth". This quotation highlights the issue of form for engineers and especially in Sarrasin's works: the affirmation of simplicity and "mathematical truth", that is to say the expression of the structural mechanics, as the engineer's aesthetic's fundamental the relation with the landscape The question of form was not only thought of in terms of efficiency and economy, or lack of decoration. The development of structural mechanics as engineer's science gave new conceptual tools allowing new designs. The first professor of civil engineering at the ETH, Karl Culmann (1821-1881), was the graphical static's father. This applied science was inspired by descriptive geometry and graphical calculation methods developed in France during the 18th and 19th century. To the construction's classical point of view distinguishing between elements bearing weight (for example pillars) and others being supported (for example lintels), graphical static opposed a spatial vision of forces interactions into the structure. New materials allowed bringing these forces into play with tensed cables, compressed or extended frames. At the beginning of the 20th century, reinforced concrete appeared as modern material along side with iron and steel. Created by builders in the 19th century, its construction method was investigated by engineers making it a universal material used by everyone, independent of patents. This assimilation was made by elaborating construction norms that had sometimes inhibitive effects on the creativity of engineers. Other engineer looked for new forms fitting the material's caracteristics. Robert Maillart (1872-1940) was one of them. He had a great influence on Sarrasin's work. The first half-century of modern engineers which started with the creation of the ETH in 1855, was a period of great innovations in science and technology. Most construction works were made of metal and were built for the railways and designed with the graphical static, creating a new architecture, but the question of aesthetic became an issue only at the beginning of the 20th century. The first reaction rose against the overwhelming presence of technology in surroundings : its impact on the landscape or on the city's image was depicted as negative. At the same time, other observers – architects, art historians – recognized in industrial constructions an aesthetical value. Some engineers wanted a come back to traditional forms as stone vaults. During the first quarter of century, several metallic bridges had been considered as fragile and replaced by stone works. Bridges were designed as monuments. On the other side, some engineers argued for the beauty of modern materials and technology, opposed to the picturesque point of view, represented by those who wanted preserving the landscape. The First World War was not only the beginning of the 20th century. It seemed also to be the moment where engineers lost their innocence. Aesthetical questions and the impact on the landscape were matters of public debates. During the same period engineering became a profession free of contractors. That had probably the effect that engineers developed their own language. Sarrasin exactly spent his study years during this period of changes. Matters of aesthetic belonged to the themes treated by his professor of structural mechanics, Arthur Rohn (1878- 1956), who considered that a bridge should not only be built rationally, but should also express his structural system. François Schüle (1860-1925), who was involved in developing constructive norms for reinforced concrete, was his professor of material's technology. He represented the scientific side of the profession of engineer. The works of Sarrasin embodied this double requirement for rationality in using materials and the will to integrate the construction works into the landscape and into the environmental context. Valais was the landscape taken into account. This mountainous district entailed contradictory representations of the need of modernization and the preservation of landscape and traditions. On one side, this region was shown as a society preserved from modernity with unchanged traditions, on the other side, the Valais quickly took part in the national economy. The landscape changed deeply with the draining of the main valley of the Rhône river, the construction of rail and road nets, industry and hydroelectric plants. Sarrasin's works were the products of this economic revolution which transformed the Valais region; they wanted at the same time to be a testimony of this story. One of the interesting aspects of the attitude of this engineer is the way he used references to ancient constructions. Beamers and arches reconsidered in respect with modern technology by use of reinforced concrete, created a dialogue with the landscape or with stoned vaults thrown upon the Alps deep abysses.

EPFL2007