Les discontinuités granulaires dans les ouvrages hydrauliques ou dans leur fondation constituent une source majeure d’instabilités à l’origine des phénomènes d’érosion. L’érosion interne est ainsi définie comme une migration de particules engendrée par un écoulement interne parasite, dans un sol ou dans un ouvrage en terre. A long terme, les conséquences de cette migration peut affecter la stabilité des ouvrages et peut même conduire à leur rupture. La sécurité des ouvrages en terre dépend principalement de la performance de leurs filtres, c’est-à-dire de la capacité du filtre, mis en interne en phase de conception ou en externe en phase de réparation, à retenir les particules fines. L’espace poral d’un filtre granulaire est divisé en volumes élémentaires, appelés pores, reliés entre eux par des étranglements plus étroits appelés constrictions. Des recherches récentes ont montré que la distribution des tailles de constriction (CSD) joue un rôle fondamental dans la compréhension des propriétés de filtration des sols granulaires. Ce travail vise à étudier la CSD et son impact sur les mécanismes de filtration dans les matériaux granulaires. Pour atteindre cet objectif, deux approches ont été suivies dans ce travail: l’une numérique et l’autre analytique. Dans le cas des matériaux de forme sphérique, la méthode des éléments discrets (DEM) permet de calculer la CSD en s’appuyant sur une partition de Delaunay en tétraèdres. Cependant, une CSD plus réaliste peut être obtenue par association des tétraèdres voisins selon un critère basé sur le chevauchement de leurs sphères de vide inscrites. A partir de cette considération et en se basant sur les modèles analytiques existants, un modèle révisé est proposé pour obtenir rapidement la CSD. Les échantillons DEM générés sont ensuite utilisés pour examiner le potentiel de transport des particules fines à travers un filtre d’épaisseur donnée. Les résultats des essais de filtration numériques menés ont montré une corrélation entre la CSD et la possibilité de migration des particules fines. En conséquence, une formule analytique a été proposée pour calculer le diamètre d’ouverture de contrôle des filtres granulaires. Cette taille caractéristique qui prend en compte la granulométrie et la densité du matériau granulaire, a été introduite dans un critère de filtre construit sur la base de la CSD, en vue de le représenter de manière plus physique. Le critère proposé reproduit correctement des résultats expérimentaux rapportés dans la littérature. / The granular discontinuities in hydraulic structures or in their foundation constitute a major source of instabilities causing erosion phenomena, process by which finer soil particles are transported through the voids between coarser particles, under seepage flow. In the long term, the microstructure of the soil will change and the excessive migration become prejudicial to the stability of the structures and may also induce their failure. The safety of earth structures is mainly dependent on the reliability of their filter performance, i.e. the ability of the filter placed inside the structure during construction or outside during repair, to retain fine particles. Indeed, the void space of a granular filter is divided into larger volumes, called pores, connected together by throats or constrictions. Recent researches showed that the distribution of throats (Constriction Size Distribution or CSD) between pores plays a key role to understand the filtration properties of a granular soil. This research is devoted to investigate the constriction sizes and their impact on the mechanisms of filtration in granular spherical materials. To achieve this objective, two approaches were followed in this work: numerical and analytical approaches. In the case of spherical materials, the Discrete Element Method (DEM) can help to compute the CSD using the Delaunay tessellation method. However, a more realistic CSD can be obtained by merging adjacent Delaunay cells based on the concept of the overlap of their maximal inscribed void spheres. Following this consideration and by extending the previously developed analytical models of CSD, a revised model is proposed to quickly obtain the CSD. The DEM data generated are then used to explore the potential of transport of fine particles through a filter of a given thickness by means of numerical filtration tests. A correlation has been found between the CSD and the possibility of migration of fine grains. Accordingly, an analytical formula has been proposed to calculate the controlling constriction size of a filter material. This characteristic size, which takes into account the particle size distribution (PSD) and the density of the material, has been used to reformulate a constriction-based criterion in a more physical manner. The proposed filter design criterion is verified based on experimental data from past studies and a good agreement has been found.

Les laboratoires sur puce visent à miniaturiser et à intégrer les fonctions couramment utilisées dans les laboratoires d'analyse afin de cibler des applications en santé avec un impact prometteur sur le diagnostic médical au lit du patient. Les membranes poreuses sont d'un grand intérêt pour la préparation et l'analyse d'échantillon sur puce car elles permettent la séparation par taille/charge de molécules, mais également leur pré-concentration. Parmi les matériaux disponibles pour constituer des membranes poreuses, le silicium poreux présente de nombreux avantages tels que le contrôle précis de la taille des pores et de la porosité, une chimie de surface pratique et des propriétés optiques uniques. Les membranes de silicium poreux sont généralement intégrées dans des puces fluidiques en les montant entre deux couches comportant des micro-canaux, formant ainsi des réseaux fluidiques à trois dimensions, peu pratiques et peu adaptés à l'observation directe par microscopie. Dans ces travaux de thèse, nous avons développé deux méthodes de fabrication de membranes de silicium à pores latéraux qui permettent leur intégration monolithique dans des systèmes microfluidiques planaires. Le premier procédé est fondé sur l'utilisation d'électrodes localement structurées afin de guider la formation de pores de manière horizontale, en combinaison avec des substrats type silicium sur isolant (SOI) pour localiser spatialement la formation de silicium poreux dans la profondeur du canal. La deuxième méthode repose sur le fait que la formation de silicium poreux par anodisation est fortement dépendante du type de dopant et de sa concentration. Bien que nous utilisons encore le même type d'électrodes structurées sur les parois latérales de la membrane pour injecter le courant lors de l'anodisation, le dopage par implantation permet de confiner la membrane, de façon analogue mais à la place de l'oxyde enterré du SOI. Des membranes à pores latéraux ont été fabriquées par ces deux méthodes et leur fonctionnalité a été démontrée en réalisant des expériences de filtrage. En plus de la filtration d'échantillon, les membranes ont été utilisées pour étudier la possibilité d'effectuer de la pré-concentration électrocinétique et de la détection interférométrique. La sélectivité ionique des membranes microporeuse permet la pré-concentration moléculaire avec des facteurs de concentration pouvant atteindre jusqu'à 103 en 10 min en appliquant moins de 9 V. Ces résultats sont comparables à ceux rapportés dans la littérature à l'aide par exemple de nanocanaux avec une consommation d'énergie beaucoup plus faible. Enfin, nous avons pu détecter une variation de l'indice de réfraction du silicium poreux par le décalage du spectre d'interférence lors du chargement de différents liquides injectés dans les membranes. Le travail présenté dans cette thèse constitue la première étape dans la démonstration de l'intérêt du silicium poreux pour la préparation d'échantillon et la biodétection dans des laboratoires sur puce planaires. / Lab on a chip devices aim at integrating functions routinely used in medical laboratories into miniaturized chips to target health care applications with a promising impact foreseen in point-of-care testing. Porous membranes are of great interest for on-chip sample preparation and analysis since they enable size- and charge-based molecule separation, but also molecule pre-concentration by ion concentration polarization. Out of the various materials available to constitute porous membranes, porous silicon offers many advantages, such as tunable pore properties, large porosity, convenient surface chemistry and unique optical properties. Porous silicon membranes are usually integrated into fluidic chips by sandwiching fabricated membranes between two layers bearing inlet and outlet microchannels, resulting in three-dimensional fluidic networks that lack the simplicity of operation and direct observation accessibility of planar microfluidic devices. To tackle this constraint, we have developed two methods for the fabrication of lateral porous silicon membranes and their monolithic integration into planar microfluidics. The first method is based on the use of locally patterned electrodes to guide pore formation horizontally within the membrane in combination with silicon-on-insulator (SOI) substrates to spatially localize the porous silicon within the channel depth. The second method relies on the fact that the formation of porous silicon by anodization is highly dependent on the dopant type and concentration. While we still use electrodes patterned on the membrane sidewalls to inject current for anodization, the doping via implantation enables to confine the membrane analogously to but instead of the SOI buried oxide box. Membranes with lateral pores were successfully fabricated by these two methods and their functionality was demonstrated by conducting filtering experiments. In addition to sample filtration, we have achieved electrokinetic pre-concentration and interferometric sensing using the fabricated membranes. The ion selectivity of the microporous membrane enables to carry out sample pre-concentration by ion concentration polarization with concentration factors that can reach more than 103 in 10 min by applying less than 9 V across the membrane[TL1]. These results are comparable to what has already been reported in the literature using e.g. nanochannels with much lower power consumption. Finally, we were able to detect a change of the porous silicon refractive index through the shift of interference spectrum upon loading different liquids into the membrane. The work presented in this dissertation constitutes the first step in demonstrating the interest of porous silicon for all-in-one sample preparation and biosensing into planar lab on a chip.

In dieser Arbeit werden Mikrosiebe mit unterschiedlichen Porendurchmessern im Mikrometer- und Submikrometerbereich mithilfe des float-casting-Verfahrens hergestellt. Im ersten Teil der Arbeit werden die Mikrosiebe mit vier unterschiedlichen Porendurchmessern mithilfe des klassischen float-casting-Verfahrens hergestellt und zu unterschiedlichen hierarchisch strukturierten Mikrosiebverbunden kombiniert. Die Permeanz der hergestellten Mikrosiebe und Mikrosiebverbunde wird theoretisch, experimentell sowie numerisch untersucht. Dabei zeigt sich, dass alle Methoden vergleichbare Werte liefern. Die Untersuchung der Filtrationseigenschaften der Mikrosiebverbunde zeigt, dass Mikrosiebe mit Porendurchmessern im Mikrometerbereich durch ihre defektfreie Struktur hervorragende Filtrationseigenschaften besitzen. Mikrosiebe mit Porendurchmessern im Submikrometerbereich weisen hingegen wenige Fehlstellen auf, die jedoch durch eine Grenzflächenpolymerisation behoben werden können. Im zweiten Teil der Arbeit wird ein Verfahren entwickelt, mit der es möglich ist, Mikrosiebe durch das Sprühen auf eine mit Partikeln besetzte Wasseroberfläche herzustellen. Dafür wird eine Apparatur für den Sprühvorgang entworfen und gebaut. Als Sprühdüse findet eine Zweistoffdüse mit äußerer Mischung Verwendung. Die verschiedenen Parameter der Sprühapparatur werden näher untersucht und im Anschluss Versuche zur Herstellung von Mikrosieben mit Porendurchmessern im Mikrometerbereich durchgeführt. Die Ergebnisse zeigen, dass sich die selbst gebaute Apparatur mit der verwendeten Zweistoffdüse zur Herstellung von Mikrosieben eignet.

Gram-negative infection has been linked to hospital water although few studies have examined whether water systems are reservoirs of nosocomial pathogens. This study investigated longitudinal recovery of the opportunistic pathogens Pseudomonas aeruginosa, Stenotrophomonas maltophilia and Acinetobacter baumannii from water outlets of a haematology unit and evaluated Point-Of-Use Filtration (POU-F) as a control measure. In a two-year double cross-over trial, water samples and swabs were taken weekly from 39 showers/taps on the unit. Four study phases alternated between non-filtered (Phases 1 & 3), and filtered outlets (Phases 2 & 4) using Pall AquasafeTM 14-day filters. In Phases 1 & 3; 99% of 1396 samples yielded bacterial growth, with colonies generally too numerous to count. Target species were isolated from 22% of water samples (P. aeruginosa 14%; S. maltophilia 10%) and 10% of swabs. P. aeruginosa was particularly associated with handwash stations and S. maltophilia with showers. A. baumannii was not isolated. With POU-F; 22% of 1242 samples yielded bacterial growth (mean CFU/100ml ,4.6). S. maltophilia was isolated only once from water but never from outlet swabs. PCR typing identified clusters of isolates colonizing different outlets over time but no clear association between water and patient isolates was identified. The incidence of Gram negative infections remained low throughout the study. Without POU-F, water from taps/showers represented a source of bacteria including the target species. POU-F substantially reduced the frequency and number of target species from every outlet, and merits further investigation as an intervention to protect immunocompromised patients from opportunistic pathogens. / School of Life Sciences, University of Bradford and Pall Medical (Pall Europe Ltd)

Clean air is a global health concern. Each year more than seven million people across the globe perish from breathing poor quality air. Development of high efficiency particulate air (HEPA) filters demonstrate an effort to mitigate dangerous aerosol hazards at the point of production. The nuclear power industry installs HEPA filters as a final line of containment of hazardous particles. Advancement air filtration technology is paramount to achieving global clean air. An exploration of analytical, experimental, computational, and machine learning models is presented in this dissertation to advance the science of air filtration technology. This dissertation studies, develops, and analyzes alternative air filtration materials and methods of analysis that optimize filtration efficiency and reduce resistance to air flow. Alternative nonwoven filter materials are considered for use in HEPA filtration. A detailed review of natural and synthetic fibers is presented to compare mechanical, thermal, and chemical properties of fibers to desirable characteristics for air filtration media. An experimental effort is undertaken to produce and evaluate new nanofibrous air filtration materials through electrospinning. Electrospun and stabilized nanofibrous media are visually analyzed through optical imaging and tested for filtration efficiency and air flow resistance. The single fiber efficiency (SFE) analytical model is applied to air filtration media for the prediction of filtration efficiency and air flow resistance. Digital twin replicas of nonwoven nanofibrous media are created using computer scripting and commercial digital geometry software. Digital twin filters are visually compared to melt-blown and electrospun filters. Scanning electron microscopy images are evaluated using a machine learning model. A convolutional neural network is presented as a method to analyze complex geometry. Digital replication of air filtration media enables coordination among experimental, analytical, machine learning, and computational air filtration models. The value of using synthetic data to train and evaluate computational and machine learning models is demonstrated through prediction of air filtration performance, and comparison to analytical results. This dissertation concludes with discussion on potential opportunities and future work needed in the continued effort to advance clean air technologies for the mitigation of a global health and safety challenge.

Thesis (M.Sc. (Microbiology)) -- University of Limpopo, 2016 / Access to safe drinking water is a major problem globally and it mostly affects people living in low-income countries. The lack of potable water leads to the use of raw water from surface or ground water sources for drinking and other household purposes. A water filtration unit was designed and constructed using fabric, gravel and sand, which were wet-packaged into a 20 L bucket. The efficiency of the filter unit to improve the bio-physicochemical properties of contaminated water was tested using surface waters from rivers in the Sekhukhune area. Physico-chemical parameters tested included turbidity, colour, total suspended solids (TSS), total dissolved solids (TDS), total hardness and pH. Turbidity and colour were the most improved characteristics, where turbidity improved by 69% and colour by 80%. Other parameters such as total hardness, TSS and TDS were non-significantly reduced following treatment with the filtration unit. The amount of soluble solids in raw water was well within allowable limits by WHO standards. Microbiological tests included heterotrophic bacteria, total coliform and faecal coliform counts. The bacterial load was too numerous to count for the untreated water, however, after treatment with the filtration unit, heterotrophic bacterial load decreased to 15 x 10103 CFU/ml, total coliforms to 14 x 10 2 CFU/100ml and faecal coliforms to 11 x 10 2 CFU/100ml. Further treatment with UV sterilization unit resulted in undetectable amount of bacteria. The unit designed in this study can be beneficial in those rural communities were clean water is not available, it is easy to construct and simple to operate and most importantly it reduced contaminants in surface water. The UV unit incorporated in this study is not cost effective, therefore, other household treatment options such as chlorination and boiling which are easily accessible to most communities can be used to further eliminate remaining microorganisms after filtration. The effective shortest boiling time and minimum dosage of Na(OCl2) have been previously tested in our laboratory and total elimination of bacteria was achieved within 2 minutes of rolling boil and after 30 minutes following addition of 5ml/20L of liquid chlorine.

Approximation theory is a fundamental tool in order to study the representation theory of a ring R. Roughly speaking, it consists in determining suitable additive or abelian subcategories of the whole module category Mod-R with nice enough functorial properties. For example, torsion theory is a well suited incarnation of approximation theory. Of course, such an idea has been generalised to the additive setting itself, so that both Mod-R and other interesting categories related with R may be linked functorially. By the seminal work of Beilinson, Bernstein and Deligne (1982), the derived category of the ring turns out to admit useful torsion theories, called t-structures: they are pairs of full subcategories of D(R) whose intersection, called the heart, is always an abelian category. The so-called standard t-structure of D(R) has as its heart the module category Mod-R itself. Since then a lot of results devoted to the module theoretic characterisation of the hearts have been achieved, providing evidence of the usefulness of the t-structures in the representation theory of R. In 2020, following a research line promoted by many other authors, Saorin and Stovicek proved that the heart of any compactly generated t-structure is always a locally finitely presented Grothendieck categories (actually, this is true for any t-structure in a triangulated category with coproducts). Essentially, this means that the hearts of D(R) come equipped with a finiteness condition miming that one valid in Mod-R. In the present thesis we tackle the problem of characterising when the hearts of certain compactly generated t-structures of a commutative ring are even locally coherent. In this commutative context, after the works of Neeman and Alonso, Jeremias and Saorin, compactly generated t-structures turned out to be very interesting over a noetherian ring, for they are in bijection with the Thomason filtrations of the prime spectrum. In other words, they are classified by geometric objects, moreover their constituent subcategories have a precise cohomological description. However, if the ascending chain condition lacks, such classification is somehow partial, though provided by Hrbek. The crucial point is that the constituents of the t-structures have a different description w.r.t. that available in the noetherian setting, yet if one copies the latter for an arbitrary ring still obtains a t-structure, but it is not clear whether it must be compactly generated. Consequently, pursuing the study of the local coherence of the hearts given by a Thomason filtration, we ended by considering two t-structures. Our technique in order to face the lack of the ascending chain condition relies on a further approximation of the hearts by means of suitable torsion theories. The main results of the thesis are the following: we prove that for the so-called weakly bounded below Thomason filtrations the two t-structures have the same heart (therefore it is always locally finitely presented), and we show that they coincide if and only they are both compactly generated. Moreover, we achieve a complete characterisation of the local coherence for the hearts of the Thomason filtrations of finite length.

No description available.

Master of Science / Department of Architectural Engineering and Construction Science / Julia A. Keen / Nanofibers are classified as fibers less than 1 micrometer in diameter. These fibers can be layered to form nanofibrous membranes, and these membranes offer great potential in the filtration industry. The membranes' smaller fiber diameters and pore sizes permit such filters to filter out more and smaller particulate. Additionally, antimicrobial agents can be incorporated into the membrane to inhibit fungal and bacterial growth on the membrane’s surface. This report evaluates nanofibrous membranes with antimicrobial agents and their potential in two specific locations: cleanrooms and protective environment rooms, where bacterial and fungal growth would have a detrimental effect on the process or occupant of the space.

This study examines perceptions of threats and the actors in the Swedish Nato-debate. The particular sequence of debate which is investigated took place in Swedish media during the summer of 2015. The objects examined in this study are the actors involved in the debate and the perceptions of threats formed by these actors. Lack of knowledge regarding how debates are formed by actors, through their perceptions of threats, makes us unable to fully comprehend how and why these perceptions are formed. This lack of knowledge makes us unable to evaluate the debate beyond the claims of the participating actors. This study seeks to explain how perceptions of threats in the chosen debate-sequence were formed through filtration. Theory considering filtration of perceived threats states that the actors forming perceived threats does this through psychological-, bureaucratic-, political- and medial processes. Actors and their perceived threats can also exercise power. Whether the actors and their discourses have exercised power in the Swedish Nato-debate is examined through a relational- and productive power perspective. Results show that the participating actors examined, scientists, journalists and politicians, have all formed perceived threats through different forms of filtration, and all actors have in some way exercised relational or productive power in the debate.