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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.
341

Simulation and Implementation of Two-Level and Three-Level Inverters by MATLAB and RT-LAB

Gebreel, Abd Almula G. M. 17 March 2011 (has links)
No description available.
342

How different forms of formative assessment can be integrated in physics lab activities.

Kjäll, Nellie, Linnarsson, Gustav January 2023 (has links)
Experiments are an important part of physics and it naturally follows that lab activities is important in physics education. While there are a great number of methods for lab activities that all have varying effects, this study seeks to answer how they interact with one of the most important tools in education, formative assessment. We have explored this topic by reviewing scientific articles on both physics lab activities as well as formative assessment in its many forms. To connect it to a more practical and Swedish context, we also surveyed Swedish physics teachers at different levels of education and performed a thematic analysis to see how they approach lab activities and what, if any, formative assessment they implement. From the scientific review we found that we can divide the physics lab activities into minimally and heavily guided. The minimally guided support abilities like critical thinking and considering sources of error, while heavily guided lab activities are more suited training procedural abilities, such as handling lab equipment, or for students with no prior experience with labs. Formative assessment can be implemented  with positive effects regardless of lab activity. Especially self and peer assessment show great results and should be viewed as a regular part of the teaching methodology for lab activities. The survey, which had 12 respondents, indicated that self and peer assessment are not used on a regular basis prior to university and the lab activities start out from heavily guided and moves towards minimally guided. The main challenge against changing both of these was time. To aid teachers in implementing the effective lab activities, proposed by the research literature, we prepared a lab activity in Swedish alongside considerations for implementations, formative assessment and a rubric.
343

Using the mixed-method approach to examine telepresence outside the lab

Sun, Weimei January 2015 (has links)
This study’s main focus is people’s experience of telepresence (or presence for short) —where the roles of technology are misperceived by media users in various ways, such as the illusion of “being there” in a mediated environment. Although over 2000 articles have examined telepresence and nearly all of research studies about telepresence have been conducted in labs by controlling and measuring the effects of different factors, with few examining it from the perspective of people’s experiences in their daily lives. Following Lombard and Sun’s (2014) (my previous study with Lombard) study of people’s presence experience outside the lab, this study used the combined results of a survey and an interview (n = 36) to explore participants’ lived experiences of presence. Participants offered basic information about them and their experience of presence in the survey; and talked about any experience of presence in their lives and specifically talk more details about their recent experience during the interviews. This study found when, where, with what kind of media, and in what situation people are more likely to have the experience of presence, and explored what elements could contribute to people’s experiences of different types of presence. The results of this study noted aftereffects of presence experiences, which means the effects presence has after people’s mediated experiences are over. These results were new findings to the study of presence outside the labs. Moreover, this study also demonstrated the value of Lombard and Sun’s (2014) survey and found two questions in the survey that could be improved. / Media Studies & Production
344

Introductory Biology Laboratory Manuals

Service, Margaret Ann 01 1900 (has links)
ABSTRACT This project describes the development and evaluation of two laboratory courses in First Year Biology, each of which is part of a larger full-year course of instruction given by the Biology Department at McMaster University. Introductory Human Physiology is prepared for Physical Education students. Adaptation in the Biological World - a general Biology course - is prepared for Natural Sciences students. Design of the laboratory exercises utilizes a variety of different educational models which are intended to stimulate the students' interest in Biology. The exercises give students first-hand experience with important principles and concepts related to the lecture material. This project stresses the role of the Teaching Assistants who supervise activities in the laboratories and who demonstrate the basic skills we expect students to learn. Conclusions drawn from this project are: 1. The majority of students consider the laboratory courses to be useful. 2. Educational goals established for the courses are being met. 3 • Change and improvement are important ongoing components of the curriculum. 4. As funds become available, we must introduce more interesting techniques and methodologies to the curriculum. 5. It is essential to maintain a high level of efficiency and organization within the team of people associated with laboratories. / Thesis / Master of Science (Teaching)
345

Synthetic Auxin Engineering: Building a Biofoundry Platform

Bryant Jr, John Alexander 03 June 2024 (has links)
Genetic regulatory circuits control metabolism, development, and environmental response across all kingdoms of life. Genetic circuit engineering facilitates sustainable and efficient production of biopharmaceutical, chemical, fiber, and food products that keep humans healthy, nourished, and clothed. However, the complexity of most genetic regulatory circuits, particularly in the context of multicellular eukaryotes, often prevents them from being leveraged as tools or applied technologies with bioeconomic relevance. However, synthetic biology enables the transfer of genes, circuits, networks, and even whole chromosomes between organisms. This approach can be leveraged to port genetic circuits into simple model organisms to control existing and engineer new cellular functions. Still, porting genes to non-native contexts can affect circuit function due to unknown factors. For this reason, iterative design-build-test-learn (DBTL) cycles are necessary for optimizing circuits in new contexts. To facilitate the DBTL cycle, automation approaches can be deployed for streamlining synthetic genetic circuits optimization. Here, I provide a case study for how using synthetic biology and automation – a biofoundry approach – has facilitated engineering of the auxin signaling pathway in a synthetic yeast system. Auxin is a phytohormone involved in nearly every aspect of plant growth and development, and this striking versatility designates it as a target for biotechnology development and a candidate for engineering. First, I provide a literature review of the history of synthetic auxin engineering in yeast, a survey of tools available for expanding yeast synthetic biology, and a summary of applicable automation tools and platforms. Next, I describe and validate a platform called AssemblyTron, which deploys liquid handling robotics for DNA assembly and can serve as the foundation of a biofoundry platform. I then introduce TidyTron, which is a protocol library for automated wash and reuse of single use lab plastics to promote biofoundry sustainability. Next, I expand the AssemblyTron package by providing protocols for mutant and modular indexed plasmid library assembly. Finally, I describe a modular indexed plasmid library (toolkit) for rapid assembly of auxin circuit variants and validate it by building and optimizing an auxin circuit. / Doctor of Philosophy / Genetic mechanisms allow humans, plants, and microbes to grow, breathe, speak, and survive. The DNA that encodes these genetic mechanisms produces protein machines that make chemicals, transfer them, and respond to them in other cells. This process is called signaling, and the protein machines involved make a circuit. In biotechnology, we harness natural genetic circuits to create important products like biopharmaceuticals, food, and clothes. However, the genetic circuits that make valuable proteins/chemicals are usually located on chromosomes along with every other gene involved in building an advanced, multicellular organism (called the genome). Synthetic biology allows us to choose just the DNA that encodes a genetic circuit of interest and put it into the chromosome of a simpler organism with faster growth, smaller genome, etc., which allow us to engineer it more easily. However, transferring a gene circuit to a new organism can cause problems, and it is usually necessary to try many versions of gene circuits to find one that works. Using robots to do synthetic biology can make it faster and less error-prone, which enables more versions of the genetic circuit to be tested. Here, I describe a biofoundry approach where I combined synthetic biology and robotics to speed up the process of building and optimizing the auxin plant hormone signaling pathway. Auxin is a small molecule that plants produce and transfer throughout their leaves, stems, and roots to turn growth on or off (e.g., auxin causes plants to do things like bend towards the sun). I focus on auxin because my goal is to manipulate the auxin pathway to rationally control plant growth. First, I provide a recap of existing work in the field of auxin synthetic biology, tools for transferring auxin circuits into simpler organisms, and available robotics that can speed up auxin synthetic biology. Next, I introduce a software called AssemblyTron, which I developed for building and modifying genes (a process called DNA assembly) with a robot. Next, I discuss how I used the same robot to wash and reuse plastic pipette tips and plates to improve lab sustainability. I then discuss an extended version of AssemblyTron that can be used for more advanced DNA assembly applications like making 10s – 100000s of versions of gene circuits at the same time. Finally, I introduce a collection of auxin circuit DNA parts that can be assembled interchangeably for rapid synthetic auxin engineering.
346

Chip-Scale Gas Chromatography

Akbar, Muhammad 04 September 2015 (has links)
Instrument miniaturization is led by the desire to perform rapid diagnosis in remote areas with high throughput and low cost. In addition, miniaturized instruments hold the promise of consuming small sample volumes and are thus less prone to cross-contamination. Gas chromatography (GC) is the leading analytical instrument for the analysis of volatile organic compounds (VOCs). Due to its wide-ranging applications, it has received great attention both from industrial sectors and scientific communities. Recently, numerous research efforts have benefited from the advancements in micro-electromechanical system (MEMS) and nanotechnology based solutions to miniaturize the key components of GC instrument (pre-concentrator/injector, separation column, valves, pumps, and the detector). The purpose of this dissertation is to address the critical need of developing a micro GC system for various field- applications. The uniqueness of this work is to emphasize on the importance of integrating the basic components of μGC (including sampling/injection, separation and detection) on a single platform. This integration leads to overall improved performance as well as reducing the manufacturing cost of this technology. In this regard, the implementation of micro helium discharge photoionization detector (μDPID) in silicon-glass architecture served as a major accomplishment enabling its monolithic integration with the micro separation column (μSC). For the first time, the operation of a monolithic integrated module under temperature and flow programming conditions has been demonstrated to achieve rapid chromatographic analysis of a complex sample. Furthermore, an innovative sample injection mechanism has been incorporated in the integrated module to present the idea of a chip-scale μGC system. The possibility of using μGC technology in practical applications such as breath analysis and water monitoring is also demonstrated. Moreover, a nanotechnology based scheme for enhancing the adsorption capacity of the microfabricated pre-concentrator is also described. / Ph. D.
347

Identifying Job Categories and Required Competencies for Instructional Technologist: A Text Mining and Content Analysis

Chen, Le 06 July 2020 (has links)
This study applied both human-based and computer-based techniques to conduct a job analysis in the field of instructional technology. The primary research focus of the job analysis was to examine the efficacy of text mining by comparing text mining results with content analysis results. This agenda was fulfilled by using job announcement data as an example to determine essential job categories and required competencies. In phase one, a job title analysis was conducted. Different categorizing strategies were explored, and primary job categories were reported. In phase two, the human-based content analysis was conducted, which identified 20 competencies in the knowledge domain, 22 in the ability domain, 23 in the skill domain, and 13 other competencies. In phase three, text mining (topic modeling) was applied to the entire data set, resulting in 50 themes. From these 50 themes, the researcher selected 20 themes that were most relevant to instructional technology competencies. The findings of the two research techniques differ in terms of granularity, comprehensibility, and objectivity. Based on evidence revealed in the current study, the author recommends that future studies explore ways to combine the two techniques to complement one another. / Doctor of Philosophy / According to Kimmons and Veletsianos (2018), text mining has not been widely applied in the field of instructional technology. This study provides an example of using text mining techniques to discover a set of required job competencies. It can be helpful to researchers unfamiliar with text mining methodology, allowing them to understand its potentials and limitations better. The primary research focus was to examine the efficacy of text mining by comparing text mining results with content analysis results. Both content analysis and text mining procedures were applied to the same data set to extract job competencies. Similarities and differences between the results were compared, and the pros and cons of each methodology were discussed.
348

Towards label-free biosensing in compact disk technologies f or point-of-need analysis

Avellà Oliver, José Miguel 01 September 2017 (has links)
Tesis por compendio / This thesis explores new analytical advances using compact disk biosensing technologies, and comprises six scientific publications distributed along four chapters. Special attention is herein payed to Thermochromic Etching Disks (TED) technology (Chapter 1), rational design of disk-based biorecognition assays (Chapter 2), and label-free detection systems for point-of-need analysis (Chapters 3 and 4). First, insights into a novel light-mediated signal developing system for biorecognition assays (based on TED disks and drives) are provided together with an overview of the state-of-the art and future trends in photo- and thermochromic biosensing. This signal developing approach exploits photo- and thermochromism for biosensing in an original manner and represents a potential strategy to simplify signaling processes in bioanalytical systems. Then, how to transform TED technology into lab-on-a-disk systems is addressed. TED has proven to be a very versatile tool to perform sensitive analysis of biorecognition assays, using platforms and scanners easily obtained from regular disks and drives, respectively. Biologically relevant assays of different nature (microarray, cell culture, immunofiltration, turbidimetry, etc.) have been arrayed in a single disk and sensitively analyzed by imaging. Regarding rational design, a theoretical-experimental method (INSEL) based on kinetics and mass-transport modelling for optimizing biorecognition assays and exploring their behavior is presented. INSEL has been implemented as an in silico tool that enables to characterize biointeractions with minimal experimentation, to perform optimizations directed towards custom objectives defined by the user, and to easily compute the effect of critical variables without further experiments. In another study included in this thesis, polycarbonate grooved structures obtained from standard recordable disks (CD-R and DVD-R) were coated with silver and tailored to become SERS-active. This strategy represents a cost-effective and industrially scalable alternative to the SERS substrates typically used for bioanalysis. These disk-based materials have presented tunable plasmonic responses, significant Raman enhancement, and have allowed complex biological targets (such as proteins and exosomes) to be analyzed by SERS without using labeled reagents as tracers. In addition to introduce inexpensive and large-scale SERS substrates for biosensing, this study also suggests the development of prospective Raman scanners based on disk drives. Another approach herein presented addresses the implementation of diffraction-based sensing (DBS) in TED technology in order to conceive disk-based label-free biosensors based on standard disks and drives. At first, a comprehensive experimental assessment of the analytical possibilities offered by DBS is presented. Then, the fabrication of arrays of diffractive protein networks on TED disks is investigated, with which sensitive analysis of antibodies in label-free conditions has been demonstrated, using adapted drives as scanners. This investigation provides important insights into cost-effective and industrially scalable functional materials and detection setups that exploit consumer electronics for label-free biosensing. / Esta tesis explora nuevos avances en química analítica usando tecnologías de biosensado basadas en sistemas de disco compacto y comprende seis publicaciones científicas distribuidas a lo largo de cuatro capítulos. Los estudios se han centrado en la tecnología Thermochromic Etching Disks (TED) (Capítulo 1), el diseño racional de ensayos de bioreconocimiento en discos compactos (Capítulo 2), y la detección sin marcaje para realizar análisis in situ (Capítulos 3 y 4). Primero, enmarcado en una discusión del estado del arte y futuras tendencias en biosensado foto y termocrómico, se presenta un nuevo sistema (basado en discos y lectores TED) mediado por luz para el desarrollo de señales en ensayos de bioreconocimiento. Ésta constituye una estrategia novedosa para aprovechar el foto y termocromismo en biosensado, y presenta un gran potencial para simplificar los procesos de desarrollo de señal en sistemas bioanalíticos. A continuación, se aborda cómo transformar la tecnología TED en sistemas analíticos integrados basados en discos compactos. TED ha demostrado ser una herramienta muy versátil para analizar, de forma sensible, ensayos de bioreconocimiento usando plataformas y escáneres fácilmente obtenidos a partir de discos y lectores convencionales, respectivamente. Un único disco ha mostrado poder albergar varios ensayos biológicos importantes y de distinta naturaleza (micromatriz, cultivos celulares, inmunofiltración, turbidimetría, etc.), para ser analizados de forma sensible a través de imágenes En cuanto al diseño racional, se presenta un método teórico-experimental (INSEL), basado en modelos cinéticos y de transporte de masa, para optimizar ensayos de bioreconocimiento y explorar su comportamiento. INSEL se ha implementado como una herramienta in silico que permite caracterizar biointeracciones mediante mínima experimentación, realizar optimizaciones dirigidas a objetivos particulares definidos por el usuario, y computar el efecto de variables críticas de forma sencilla y sin experimentos adicionales. En otro estudio incluido en esta tesis, nanoestructuras en forma de surco obtenidas a partir de discos regrabables convencionales (CD-R y DVD-R) fueron recubiertas con plata y adaptadas para ser activas en SERS. Esta estrategia supone una alternativa, económicamente efectiva e industrialmente escalable, a los sustratos SERS típicamente usados en bioanálisis. Estos materiales han mostrado respuestas plasmónicas sintonizables, una amplificación Raman significativa, y han permitido analizar muestras biológicas complejas (como proteínas y exosomas) mediante SERS sin usar marcadores. Además de introducir sustratos SERS grandes y baratos, este trabajo también sugiere el desarrollo de escáneres Raman basados en lectores de disco. Otra aproximación presentada en esta tesis aborda la implementación de DBS (diffraction-based sensing) en tecnologías TED, con el fin de desarrollar biosensores para detección sin marcaje basados en discos y lectores convencionales. Primero, se presenta una amplia evaluación experimental de las posibilidades analíticas ofrecidas por DBS. A continuación, se investiga la fabricación de multitud de redes difractivas de proteínas sobre discos TED, con las que se ha demostrado la determinación sensible y sin marcaje de anticuerpos, usando lectores adaptados como escáneres analíticos. Esta investigación introduce avances importantes que apuntan al desarrollo de materiales funcionales y sistemas de detección, baratos e industrialmente escalables, que aprovechen las tecnologías de consumo para realizar biosensado sin marcaje. / Aquesta tesi explora nous avanços en la química analítica usant tecnologies de biosensat basades en sistemes de disc compacte, i comprèn sis publicacions científiques distribuïdes en quatre capítols. Els estudis s'han centrat en la tecnologia Thermochromic Etching Disks (TED) (Capítol 1), el disseny racional d'assajos de bioreconeixement en discos compactes (Capítol 2), i la detecció sense marcatge per realitzar anàlisi in situ (Capítols 3 i 4). Primer, dins del marc d'una discussió de l'estat de l'art i tendències futures en biosensat foto i termocròmic, es presenta un nou sistema (basat en discos i lectors TED) per al desenvolupament de senyals mitjançant llum, en assajos de bioreconeixement. Aquesta constitueix una nova estratègia per aprofitar el foto i termocromisme en biosensat, mentre que també presenta una gran potencial per simplificar els processos de desenvolupament de senyal en sistemes bioanalítics. Tot seguit, s'aborda com transformar la tecnologia TED en sistemes analítics integrats basats en discos compactes. TED ha demostrat ser una eina molt versàtil per analitzar, de forma sensible, assajos de bioreconeixement usant plataformes i escàners fàcilment obtinguts a partir de discos i lectors convencionals, respectivament. Un únic disc ha mostrat poder albergar diversos assajos biològicament importants i de distinta naturalesa (micromatrius, cultius cel·lulars, immunofiltració, turbidimetria, etc.), per a ser analitzats de forma sensible a través d'imatges. Pel que fa al disseny racional, es presenta un mètode teòric-experimental (INSEL), basat en models cinètics i de transport de massa, per optimitzar assajos de bioreconeixement i explorar el seu comportament. INSEL s'ha implementat com a una eina in silico que permet caracteritzar biointeraccions amb mínima experimentació, realitzar optimitzacions dirigides cap a objectius particulars definits per l'usuari, i computar l'efecte de variables crítiques de forma senzilla i sense experiments addicionals. En un altre estudi inclòs en aquesta tesi, nanoestructures en forma de solc obtingudes a partir de discos compactes regravables convencionals (CD-R i DVD-R) van ser recobertes amb plata i adaptades per a ser actives en SERS. Aquesta estratègia suposa una alternativa, econòmicament efectiva i industrialment escalable, als substrats SERS típicament usats en bioanàlisi. Aquests materials han mostrat respostes plasmòniques sintonitzables, una amplificació Raman significativa, i han permès analitzar mostres biològiques complexes (com proteïnes i exosomes) mitjançant SERS sense usar marcadors. A més d'introduir substrats SERS grans i barats, aquest treball també suggereix el desenvolupament d'escàners Raman basats en lectors de disc. Una altra aproximació presentada en aquesta tesi aborda la implementació de DBS (diffraction-based sensing) en tecnologies TED, per tal de desenvolupar biosensors basats en discos i lectors convencionals que permeten detecció sense marcatge. Primer, es presenta una amplia avaluació experimental de les possibilitats analítiques que ofereix aquesta tècnica. A continuació, s'investiga la fabricació de multitud de xarxes difractives de proteïnes sobre discos TED, amb les quals s'ha demostrat la determinació sensible i sense marcatge d'anticossos, usant lectors adaptats com a escàners analítics. Aquesta investigació introdueix avanços importants que apunten cap al desenvolupament de materials funcionals i sistemes de detecció, barats i industrialment escalables, que aprofiten les tecnologies de consum per dur a terme bioanàlisi sense marcatge. / Avellà Oliver, JM. (2017). Towards label-free biosensing in compact disk technologies f or point-of-need analysis [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86128 / Compendio
349

Predicting Pallet Part Yields From Hardwood Cants

Mitchell, Hal Lee 05 March 1999 (has links)
Pallet cant quality directly impacts pallet part processing and material costs. By knowing the quality of the cants being processed, pallet manufacturers can predict costs to attain better value from their raw materials and more accurately price their pallets. The study objectives were 1) to develop a procedure for accurately predicting hardwood pallet part yield as a function of raw material geometry and grade, processing equipment, and pallet part geometry, 2) to develop a model for accurately predicting raw material costs for hardwood pallet parts as a function of yield, 3) to examine current pallet industry methods of determining hardwood cant quality, and 4) to develop and evaluate hardwood cant grading rules for use in the pallet industry. Yield studies were necessary to accurately quantify the relationship between yield and cant quality. Thirty-one yield studies were conducted throughout the Eastern United States at pallet mills producing pallet parts from hardwood cants. 47, 258 board feet of hardwood cants were graded, and the usable pallet part yield and yield losses were determined for each grade. Yield losses were separated into three components: kerf loss, dimension loss, and defect loss. Kerf and dimension losses are a function of raw material and part geometry and were calculated without regard to cant quality. Defect loss is dependent on cant quality and was calculated for each cant grade as a function of total yield, kerf loss, and dimension loss. Mathematical models were developed from twenty-eight mill studies to predict each yield loss component as a function of cant dimensions, grade, and orientation, cutting bill parameters, pallet part dimensions, and kerf. Dimension and kerf losses were predicted geometrically. Regression analysis was used to predict defect loss. Results indicated that these models accurately predicted the total yield of usable pallet parts and pallet part material costs as a function of cant quality and price. Results also indicated that the pallet industry's current method of counting the number of "bad" ends per cant bundle to determine cant quality is not adequate. The effectiveness of the proposed cant grading rules was determined by grading cants and analyzing the cant grade distributions and corresponding pallet part yields. The grade rules produced statistically different quality divisions between grades. However, a more practical single cant grade based on the minimum quality for the proposed grade 2 rules is recommended. / Master of Science
350

Highly structured polymer foams from liquid foam templates using millifluidic lab-on-a-chip techniques / Mousses polymères hautement structurées à partir de modèles de mousses liquides obtenues à l'aide de techniques millifluidiques

Testouri, Aouatef 08 October 2012 (has links)
Les mousses polymères appartiennent à la famille des mousses solides qui sont des matériaux polyvalents, largement utilisés dans un grand nombre d'applications telles que l'automobile, l'emballage, produits de sport, isolants thermiques et acoustiques ou l'ingénierie tissulaire. Composé de bulles d'air piégées dans un réseau continu solide, elles allient les propriétés du polymère avec ceux de la mousse pour créer un matériau intéressant et complexe. L'intégration d'une mousse dans un réseau de polymère permet non seulement d'utiliser la vaste gamme de propriétés intéressantes offertes par les polymères, mais permet aussi de profiter des propriétés avantageuses des mousse telles que la légèreté, la faible densité, la compressibilité et un rapport surface/volume grande surface élevé. En général, les propriétés des mousses polymères sont fortement liées à leur densité et leur structure (la taille des bulles, l’arrangement des bulles dans l’espace, la structure des cellules ouvertes ou fermées). Le contrôle des propriétés finales de ces mousses est donc régi par le contrôle de sa densité et sa structure.Nous avons développé une technique dans laquelle des mousses solides sont générées essentiellement suivant un processus à deux étapes dans lequel une mousse liquide suffisamment stable ayant des propriétés bien contrôlées est générée dans une première étape, puis solidifiée. Avec une telle approche, la production des mousses solides peut être divisé en un certain nombre de sous-tâches qui peuvent être contrôlées et optimisées séparément.Le passage de l'état liquide à l'état solide est essentiellement composé de trois étapes principales: la production de la mousse, le mélange des réactifs et la solidification de la mousse. Ce dernier nécessite l'optimisation de la stabilité de la mousse et des paramètres expérimentaux tels que le choix du temps de moussage et de solidification. En outre, une bonne homogénéité de la mousse polymère appelle à un bon mélange des différents réactifs impliqués dans la formulation de la mousse et de la polymérisation.Une illustration des avantages de cette approche est donnée par la solidification de mousses liquides monodisperses générées à l’aide de la technique millifluidique. Dans une telle mousse, des bulles de volume égal, s’auto-organisent sous l’effet de la gravité et du confinement pour former des structures cristallines. Ainsi, les mousses monodisperses permettent d’avoir un contrôle simultanément sur la taille et la distribution des bulles du matériau poreux final, ce qui donne lieu à une meilleure compréhension de la corrélation entre sa structure et ses propriétés. L’objectif de cette étude est donc d'explorer le nouveau spectre de propriétés, que des mousses polymère offrent lorsque l’on y introduit une structure ordonnée et de démontrer la faisabilité de cette approche à deux étapes pour différentes classes de polymères (hydrogel, polymère super-absorbant et polyuréthane).La génération de ces mousses polymères structurées a été réalisée à l’aide d’un laboratoire sur puce qui permet le rétrécissement des dispositifs expérimentaux à l'échelle micro / millimétrique. Il permet également l’injection et le mélange divers ingrédients liquides et gazeux de la mousse. / Polymer foams belong to the solid foams family which are versatile materials, extensively used for a large number of applications such as automotive, packaging, sport products, thermal and acoustic insulators, tissue engineering or liquid absorbents. Composed of air bubbles entrapped in a continuous solid network, they combine the properties of the polymer with those of the foam to create an intriguing and complex material. Incorporating a foam into a polymer network not only allows one to use the wide range of interesting properties that the polymer offers, but also permits to profit from the advantageous properties of foam including lightness, low density, compressibility and high surface-to-volume ratio. Generally, the properties of polymer foams are strongly related to their density and their structure (bubble size and size distribution, bubble arrangement, open vs closed cells). Having a good control over foam properties is thus achieved by first controlling its density and structure.We developed a technique in which solid foams are generated essentially in a two-step process: a sufficiently stable liquid foam with well-controlled structural properties is generated in a first step, and then solidified in a second one. With such a two-step approach, the generation of solid foams can be divided into a number of well-separated sub-tasks which can be controlled and optimised separately. The transition from liquid to solid state is a sensitive issue of a great importance and therefore needs to be controlled with sufficient accuracy. It is essentially composed of three key steps: foam generation, mixing of reactants and foam solidification and requires the optimisation of foam stability in conjunction with an appropriate choice of both foaming time and solidification time. Furthermore, a good homogeneity of the polymer foam calls for a good mixing of the different reactants involved in the foaming and the polymerisation.A particularly powerful demonstration of the advantages of this approach is given by solidifying monodisperse liquid foams generated using millifluidic technique, in which all bubbles have the same size. In a liquid foam, equal-volume bubbles self-order into periodic, close-packed structures under gravity or confinement. As such, monodisperse foams provide simultaneous control over the size and the organisation of the pores in the final solid with an accuracy which is expected to give rise to a better understanding of the structure-property relationship of porous solids and to the development of new porous materials.We therefore aim to explore the new spectrum of properties, which polymer foams offer when we introduce an ordered structure into them since the most widely used polymer foams nowadays have disordered structures. The goal of our study is to demonstrate the feasibility of this two-step approach for different classes of polymers, including biomolecular hydrogel, superabsorbent polymer and polyurethane.For the generation of the structured polymer foams we use Lab-on-a-Chip technologies which allow the “shrinking” of large-scale set-ups to micro/millimetic scale. It permits also to perform “flow chemistry” in which the various liquid and gaseous ingredients of the foam are injected and mixed in a purpose-designed network of the micro- and millifluidic Lab-on-a-Chip. We adjust this approach according to the requirements of each polymer system, i.e. the foaming and the mixing techniques are chosen to fit the properties of each system, and can be exchanged to fit the properties of the studied systems.

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