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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Produktion unter Risiko : ein agentenbasiertes, sektorales Partialmodell zur Anwendung in der Nachhaltigkeitsforschung / Production under risk

Meißner, Frank January 2007 (has links)
Mit der hier vorliegenden Arbeit wird ein mikroökonomisches Multiagentenmodell eines Produktionssektors vorgeschlagen. Das Modell folgt einem post-walrasianischem Ungleichgewichtsansatz und beschreibt optimierende Agenten der Produktionsseite. Diese berücksichtigen in probabilistischen Nebenbedingungen Risiken des Cash Flow, die sich aus unsicheren Absatzmengen ergeben. Produzenten stehen in monopolistischer Konkurrenz und lernen durch Beobachten. Wird vorliegendes Modell in ein Totalmodell integriert, so wird es möglich, die sich aus der Klimadebatte ergebenden, notwendigen Veränderungen im Investitions- und Produktionsverhalten zu diskutieren und darzustellen. / In the following thesis I propose a microeconomic Multi-Agent-Model of a production sector. I apply a Post-Walrasian disequilibrium approach and describe optimizing agents. These agents use chance constraints which depict a Cash Flow at Risk approach. Agents act in a Monopolistic-Competition environment.
12

A fast, scalable acoustic resonator-based biosensor array system for simultaneous detection of multiple biomarkers

Munir, Farasat 17 August 2012 (has links)
This thesis is about the design of a biosensor system for detection of multiple cancer biomarkers. Accurate diagnosis and prognosis of cancer requires early detection. Equally important, though, is the measurement of biomarker-velocity and detection of multiple biomarkers. Early detection requires highly sensitive biosensors capable of detection at very low concentrations of target molecules. Biomarker-velocity can be measured by monitoring concentration of target molecule over a period of time. This requires a system which is very easy to use, fast, flexible, inexpensive and portable, thus enabling its ubiquitous presence at the point of care. For detection of multiplexed biomarkers, biosensors which easily lend to array configuration are required. Conventional techniques do not fulfill either all or some aspects of the requirements listed above. In this work, we present the design of a biosensor system, keeping in view the desired features described above, to achieve the ultimate goal of enabling ubiquitous presence of biosensor at the point of care. We focus on acoustic transducer based biosensors. The two fundamental components of design in an acoustic biosensor are the design of an acoustic transducer and the design of a novel electrical interface for the transducer. For transducer design, we introduce and present the design of a single structure, GHz range, multi-mode acoustic resonator. We present this as a suitable transducer for liquid phase biosensors, which is the preferred medium for sensing of cancer biomarkers. We explore the underlying physics and do experimental and theoretical characterization of this device. The transducer needs to be functionalized with a chemically sensitive layer which performs the molecular recognition of cancer biomarkers. We present the experimental exploration of a reversible and oriented immobilization based Histidine-Ni(2+) interaction which used NTA as the chelator for anchoring onto the device. Then we discuss the microfluidic design to enable liquid phase operation. We used SU-8 polymer barriers for liquid containment and addressed the challenges of making it compatible with ZnO based devices. An electrical interface is needed to excite and extract the sensor response. We have presented here a novel method to measure and track a resonator's response and extract its characteristic parameters. This method measures the wideband frequency response of the resonator with a much simpler setup as compared to conventional methods. We have proposed and demonstrated the use of a white noise signal as a viable signal for broadband excitation of resonator-based sensing platforms. We have also established, shown through simulation and prototype measurements, the feasibility of the proposed method. The accuracy and speed of the system can be further greatly improved by FFT-based digital implementation of the spectral analysis system. We have presented an example hardware implementation of FFT-based signal analyzer, and have discussed the hardware resources required for actual implementation in a chip form. Lastly we discuss the measurement protocol and sensor results for head and neck cancer and prostate cancer biomarkers. These results demonstrate the usability of the proposed sensor system for detection of cancer biomarkers.
13

Development and validation of models for bubble coalescence and breakup

Liao, Yixiang 20 February 2014 (has links) (PDF)
A generalized model for bubble coalescence and breakup has been developed, which is based on a comprehensive survey of existing theories and models. One important feature of the model is that all important mechanisms leading to bubble coalescence and breakup in a turbulent gas-liquid flow are considered. The new model is tested extensively in a 1D Test Solver and a 3D CFD code ANSYS CFX for the case of vertical gas-liquid pipe flow under adiabatic conditions, respectively. Two kinds of extensions of the standard multi-fluid model, i.e. the discrete population model and the inhomogeneous MUSIG (multiple-size group) model, are available in the two solvers, respectively. These extensions with suitable closure models such as those for coalescence and breakup are able to predict the evolution of bubble size distribution in dispersed flows and to overcome the mono-dispersed flow limitation of the standard multi-fluid model. For the validation of the model the high quality database of the TOPFLOW L12 experiments for air-water flow in a vertical pipe was employed. A wide range of test points, which cover the bubbly flow, turbulent-churn flow as well as the transition regime, is involved in the simulations. The comparison between the simulated results such as bubble size distribution, gas velocity and volume fraction and the measured ones indicates a generally good agreement for all selected test points. As the superficial gas velocity increases, bubble size distribution evolves via coalescence dominant regimes first, then breakup-dominant regimes and finally turns into a bimodal distribution. The tendency of the evolution is well reproduced by the model. However, the tendency is almost always overestimated, i.e. too much coalescence in the coalescence dominant case while too much breakup in breakup dominant ones. The reason of this problem is discussed by studying the contribution of each coalescence and breakup mechanism at different test points. The redistribution of the gaseous phase from the injection position at the pipe wall to the whole cross section is overpredicted by the Test Solver especially for the test points with high superficial gas velocity. Besides the models for bubble forces, the simplification of the Test Solver to a 1D model has an influence on the redistribution process. Simulations performed using CFX show that a considerable improvement is achieved with comparison to the results delivered by the standard closure models. For the breakup-dominant cases, the breakup rate is again overestimated and the contribution of wake entrainment of large bubbles is underestimated. Furthermore, inlet conditions for the liquid phase, bubble forces as well as turbulence modeling are shown to have a noticeable influence, especially on the redistribution of the gaseous phase.
14

Kan korslaminerat trä effektivisera ett byggsystem : En jämförelse av flervåningshus i trä

Svennberg, Renny, Torstensson, Mikael January 2017 (has links)
The construction of wooden multi-storey buildings creates issues with the acoustic environment. To meet Boverkets soundproofing requirements the solutions of today results in thick partition building components taking up potential floor space. Crosslaminatedtimber is a solid timber slab that can be manufactured in varying sizes and thicknesses. These boards can then be used as supporting elements in walls, ceilings and floors. This study investigates whether cross-laminated timber can be used to streamline the construction of multi-storey wooden buildings. In this comparative survey a reference building constructed by A-hus was used and current loads, sound insulation, use of floorspace and economy were analyzed. Four different alternative walls and one floor constructed with cross-laminated timber have been studied according to the above named criteria, and then compared with the reference building. The result indicates that a wall with 80 mm cross-laminated timber board has the load capacity required, improves sound insulation and saving 16 m2 of floorspace in the reference building valued to approximately 695,000 SEK in increased sales revenue. Using cross-laminated timber in the floor does not sufficient improve A-hus current construction system and should therefore not be interesting.
15

Development and validation of models for bubble coalescence and breakup

Liao, Yixiang January 2013 (has links)
A generalized model for bubble coalescence and breakup has been developed, which is based on a comprehensive survey of existing theories and models. One important feature of the model is that all important mechanisms leading to bubble coalescence and breakup in a turbulent gas-liquid flow are considered. The new model is tested extensively in a 1D Test Solver and a 3D CFD code ANSYS CFX for the case of vertical gas-liquid pipe flow under adiabatic conditions, respectively. Two kinds of extensions of the standard multi-fluid model, i.e. the discrete population model and the inhomogeneous MUSIG (multiple-size group) model, are available in the two solvers, respectively. These extensions with suitable closure models such as those for coalescence and breakup are able to predict the evolution of bubble size distribution in dispersed flows and to overcome the mono-dispersed flow limitation of the standard multi-fluid model. For the validation of the model the high quality database of the TOPFLOW L12 experiments for air-water flow in a vertical pipe was employed. A wide range of test points, which cover the bubbly flow, turbulent-churn flow as well as the transition regime, is involved in the simulations. The comparison between the simulated results such as bubble size distribution, gas velocity and volume fraction and the measured ones indicates a generally good agreement for all selected test points. As the superficial gas velocity increases, bubble size distribution evolves via coalescence dominant regimes first, then breakup-dominant regimes and finally turns into a bimodal distribution. The tendency of the evolution is well reproduced by the model. However, the tendency is almost always overestimated, i.e. too much coalescence in the coalescence dominant case while too much breakup in breakup dominant ones. The reason of this problem is discussed by studying the contribution of each coalescence and breakup mechanism at different test points. The redistribution of the gaseous phase from the injection position at the pipe wall to the whole cross section is overpredicted by the Test Solver especially for the test points with high superficial gas velocity. Besides the models for bubble forces, the simplification of the Test Solver to a 1D model has an influence on the redistribution process. Simulations performed using CFX show that a considerable improvement is achieved with comparison to the results delivered by the standard closure models. For the breakup-dominant cases, the breakup rate is again overestimated and the contribution of wake entrainment of large bubbles is underestimated. Furthermore, inlet conditions for the liquid phase, bubble forces as well as turbulence modeling are shown to have a noticeable influence, especially on the redistribution of the gaseous phase.
16

Modélisation de l'évaporation des films liquides minces, y compris au voisinage des lignes de contact: application aux caloducs à rainures

Rossomme, Séverine 17 December 2008 (has links)
Les recherches que nous présentons dans ce manuscrit s’inscrivent dans le cadre de l’analyse des phénomènes de transport fondamentaux impliqués lors du processus d’évaporation d’un film liquide mince. Outre les mécanismes macroscopiques (résistance thermique du solide, capillarité, thermocapillarité, …) qui influencent le comportement de tels films, des développements fondamentaux et expérimentaux ont mis en évidence le rôle significatif d’effets microscopiques, comme les forces de van der Waals [11,96,117]. L’objectif de cette thèse est double. Il s’agit tout d’abord de caractériser les phénomènes locaux qui influencent le processus d’évaporation et ensuite, d’étendre notre étude à une échelle globale “macroscopique”. Ce manuscrit est divisé en deux parties qui correspondent à ces deux objectifs. <p><p>L’étude décrite dans la première partie propose une contribution originale à la modélisation de l’évaporation des films minces, y compris au voisinage des lignes de contact. De manière générale, nous cherchons à mettre en évidence l’influence de phénomènes qui se déroulent aux petites échelles sur le transfert thermique d’un film mince déposé sur une paroi plane et chauffée. Dans le cadre de l’hypothèse de lubrification, deux modèles sont dès lors développés. Le premier modèle décrit l’évaporation d’un film liquide mince dans sa vapeur pure tandis que le second modèle porte sur l’évaporation d’un film liquide mince dans un gaz inerte. Les diverses recherches menées sont principalement orientées vers la quantification, d’une part, des angles de contact apparents générés par l’évaporation, malgré le caractère parfaitement mouillant du couple liquide-solide utilisé et, d’autre part, des flux de chaleur et de matière interfaciaux. Une particularité du premier modèle est qu’il généralise divers modèles existants [15,25,86,117] en regroupant un ensemble de phénomènes spécifiques et complexes tels que le saut de température à l’interface liquide-vapeur, la résistance thermique de la vapeur et celle du solide ou la variation locale de la température de saturation à l’interface liquide-vapeur suite à la courbure interfaciale et aux forces de van der Waals. En plus de ces effets, d’autres mécanismes plus classiques sont inclus dans le modèle :la tension superficielle, la thermocapillarité, la pression de disjonction, l’évaporation et le recul de vapeur. Des analyses de stabilité linéaires et des études paramétriques ont été réalisées afin de quantifier l’influence de ces phénomènes sur la stabilité d’un film liquide mince, sur son évaporation et sur le transfert de chaleur associé. Au travers des chapitres 3 et 4, nous mettons notamment en évidence <p>• comment les forces de van der Waals compensent l’évaporation du film liquide mince de façon à créer un film stationnaire stable,<p>• pourquoi le recul de la vapeur et la thermocapillarité sont deux phénomènes qui peuvent être négligés dans les conditions étudiées dans ce travail,<p>• des lois analytiques qui décrivent certaines variables du problème, plus particulièrement l’angle de contact et le maximum du flux de chaleur, en fonction de la surchauffe de la paroi solide.<p><p>Faisant suite aux travaux proposés par Haut et Colinet [59], nous avons ensuite développé un second modèle afin de caractériser l’évaporation dans une faible quantité de gaz inerte d’un film liquide mince déposé sur une paroi plate et chauffée. Tout comme dans le cadre de l’étude précédente, notre analyse s’articule autour d’une étude de stabilité linéaire ainsi que d’études paramétriques réalisées sur des nombres caractéristiques du problème. Alors que les conclusions sur la stabilité du film sont indépendantes de la quantité de gaz inerte contenue dans la phase vapeur, il n’en est pas de même pour les transferts de matière et de chaleur interfaciaux comme montré au chapitre 5.<p><p>Dans la seconde partie du travail, nous utilisons les conclusions auxquelles nous sommes arrivés dans la première partie dans le cadre d’une application industrielle. En collaboration avec le Centre d’Excellence en Recherche Aéronautique (CENAERO) et la société Euro Heat Pipes (EHP), une stratégie a été élaborée afin de simuler les transferts thermiques radiaux dans une rainure d’un caloduc au niveau de l’évaporateur. Les résultats numériques, obtenus sur base d’un modèle multi-échelle développé à l’ULB et implémenté numériquement lors d’un stage chez CENAERO, montrent que ces transferts sont influencés par la valeur de l’angle de contact. Celui-ci dépendant des phénomènes microscopiques, il s’avère par conséquent nécessaire de les inclure dans le modèle thermique. En effet, si nous ne considérons que les aspects macroscopiques du problème, qui se résument à la conduction dans le solide et dans le liquide, le coefficient d’échange global au niveau de la rainure est surestimé.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished
17

Machine Learning Based Prediction and Classification for Uplift Modeling / Maskininlärningsbaserad prediktion och klassificering för inkrementell responsanalys

Börthas, Lovisa, Krange Sjölander, Jessica January 2020 (has links)
The desire to model the true gain from targeting an individual in marketing purposes has lead to the common use of uplift modeling. Uplift modeling requires the existence of a treatment group as well as a control group and the objective hence becomes estimating the difference between the success probabilities in the two groups. Efficient methods for estimating the probabilities in uplift models are statistical machine learning methods. In this project the different uplift modeling approaches Subtraction of Two Models, Modeling Uplift Directly and the Class Variable Transformation are investigated. The statistical machine learning methods applied are Random Forests and Neural Networks along with the standard method Logistic Regression. The data is collected from a well established retail company and the purpose of the project is thus to investigate which uplift modeling approach and statistical machine learning method that yields in the best performance given the data used in this project. The variable selection step was shown to be a crucial component in the modeling processes as so was the amount of control data in each data set. For the uplift to be successful, the method of choice should be either the Modeling Uplift Directly using Random Forests, or the Class Variable Transformation using Logistic Regression. Neural network - based approaches are sensitive to uneven class distributions and is hence not able to obtain stable models given the data used in this project. Furthermore, the Subtraction of Two Models did not perform well due to the fact that each model tended to focus too much on modeling the class in both data sets separately instead of modeling the difference between the class probabilities. The conclusion is hence to use an approach that models the uplift directly, and also to use a great amount of control data in each data set. / Behovet av att kunna modellera den verkliga vinsten av riktad marknadsföring har lett till den idag vanligt förekommande metoden inkrementell responsanalys. För att kunna utföra denna typ av metod krävs förekomsten av en existerande testgrupp samt kontrollgrupp och målet är således att beräkna differensen mellan de positiva utfallen i de två grupperna. Sannolikheten för de positiva utfallen för de två grupperna kan effektivt estimeras med statistiska maskininlärningsmetoder. De inkrementella responsanalysmetoderna som undersöks i detta projekt är subtraktion av två modeller, att modellera den inkrementella responsen direkt samt en klassvariabeltransformation. De statistiska maskininlärningsmetoderna som tillämpas är random forests och neurala nätverk samt standardmetoden logistisk regression. Datan är samlad från ett väletablerat detaljhandelsföretag och målet är därmed att undersöka vilken inkrementell responsanalysmetod och maskininlärningsmetod som presterar bäst givet datan i detta projekt. De mest avgörande aspekterna för att få ett bra resultat visade sig vara variabelselektionen och mängden kontrolldata i varje dataset. För att få ett lyckat resultat bör valet av maskininlärningsmetod vara random forests vilken används för att modellera den inkrementella responsen direkt, eller logistisk regression tillsammans med en klassvariabeltransformation. Neurala nätverksmetoder är känsliga för ojämna klassfördelningar och klarar därmed inte av att erhålla stabila modeller med den givna datan. Vidare presterade subtraktion av två modeller dåligt på grund av att var modell tenderade att fokusera för mycket på att modellera klassen i båda dataseten separat, istället för att modellera differensen mellan dem. Slutsatsen är således att en metod som modellerar den inkrementella responsen direkt samt en relativt stor kontrollgrupp är att föredra för att få ett stabilt resultat.

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