L’objectif de ce travail est d’approfondir les connaissances sur les phénomènes mis en jeu lors de la combustion de carburant liquide dispersé sous forme d’aérosol. De nombreux propulseurs (moteurs de fusée, turbines à gaz, moteurs à combustion interne..) reposent sur la combustion de combustibles initialement sous forme liquide. Or, la combustion diphasique est un phénomène très complexe faisant intervenir de nombreux processus: atomisation, interaction entre gouttelettes, vaporisation, écoulement diphasique, cinétique chimique, propagation de flamme. Tous ces phénomènes étant couplés, une description complète est seulement possible par le biais de simulations numériques ; mais les investigations expérimentales sont nécessaires pour fournir des données aussi quantitatives que possible dans des configurations simples afin de proposer ou de confirmer des modèles prenant en compte ces couplages. Ainsi, des études théoriques, expérimentales et numériques, doivent être menées en parallèle pour accroître les connaissances dans le domaine de la combustion diphasique et améliorer le fonctionnement des applications actuelles. Ce travail a été initié dans le cadre du Groupement de Recherche « Micropesanteur Fondamentale et Appliquée » du CNRS et du CNES, en 2008. Il est la suite des précédents travaux sur la vaporisation et la combustion des gouttes en microgravité conduites à ICARE et soutenus par le CNES durant de longues années. Cette nouvelle étude a essentiellement porté sur la détermination expérimentale des vitesses de propagation des flammes dans un aérosol (ou brouillard). Elle s’est appuyée sur l'utilisation d’une chambre de combustion haute pression développée à ICARE. Les expériences ont été principalement conduites sous des conditions de gravité réduite, pour éviter les problèmes de sédimentation de la phase dispersée. Cet appareillage a été conçu et élaboré pour être utilisé à bord de l’Airbus A300-0g du CNES. / Spray and aerosol cloud combustion accounts for 25% of the world’s energy use, and yet it remains poorly understood from both a fundamental and a practical perspective. Realistic sprays have a liquid breakup region, a dispersed multiphase flow, turbulent mixing processes, and various levels of flame interactions through the spray. Idealization of spray configurations in a quiescent environment (the starting point for models) has been impossible in 1 g due to the settling of large droplets and the buoyant pluming of post combustion gases. Testing in microgravity conditions relates to the possibility of creating aerosols without sedimentation effects. This research was to determine experimentally the flame propagation velocity in aerosols. First, the size of droplets in the aerosol was characterized using a laser diffraction particle size analyzer “Sympatec-HELOS”, and using ethanol as fuel. Second, high-Pressure combustion studies were performed using a high-Pressure combustion chamber (max pressure 12 MPa). These pieces of equipment were designed to be used in microgravity while aboard the Airbus A300-0g of the CNES. After ground tests, five parabolic flight campaigns were conducted. A systematic comparative analysis for identical initial conditions in both normal and reduced gravity was performed. The effects of initial temperature and pressure on the droplet diameter distribution of the aerosol, the effects of gravity on the flame behavior for both vapor-Air and droplet-Vapor-Air mixtures, and the effect of drops size on the flame speed and structure were all studied.

Doctor of Philosophy / Department of Biology / Stephen Chapes / Antibodies are an essential part of the immune system. Each B cell, a type of white blood cell, produces a unique antibody. This antibody molecule is comprised of two identical light chains and two identical heavy chains. Each chain has a variable region, which is responsible for antigen binding, and a constant region, which is responsible for effector function in the host. The variable region in the heavy chain is composed of three gene segments, the variable (V), diversity (D), and joining (J) gene segments. The light chain is composed of only V- and J-gene segments. Each immunoglobulin locus contains multiple versions of each gene segment, ranging from over 130 possible V gene segments in the heavy chain to four possible J-gene segments in both the heavy and kappa light chain. The recombination of gene segments occurs in the germline DNA and results in the formation of the unique antibody. The diversity and binding abilities of the antibodies are important for a proper and robust immunological response. Of importance to binding and specificity is the complementary determining region three (CDR3) which plays a major role in determining specificity and antibody-antigen binding. Due to its uniqueness, is used as a measure of diversity in the repertoire. In this work, I used Illumina MiSeq 2x300nt high-throughput sequencing to assess the mouse splenic transcriptome. The work I present here shows the splenic immunoglobulin gene repertoire from unchallenged, unvaccinated conventionally housed mice, mice flown aboard the International Space Station (ISS), and mice challenged with tetanus toxoid (TT) and/or adjuvant (CpG) and subjected to skeletal unloading by antiorthostatic suspension (AOS). AOS is used to induce some of the physiological changes that parallel those that occur during space flight. The characterization of the repertoire includes analysis of V-, D-, and J-gene segment usage, constant region usage, V- and J-gene segment pairing, and CDR3 length and usage. The work included validation of the methodology needed for tissue preparation and storage aboard the ISS, showing that the data obtained was similar to those used in standard ground-based methodologies (Chapter 2). I further validated our nonamplified sequencing methodology with comparisons to methods that use amplification as part of the process (Chapter 3). My work characterized the antibody repertoire of the conventionally housed C57BL/6J mouse (Chapter 4), an important mouse strain in the field of immunology, and demonstrated the homogeneity of gene segment usage in unchallenged animals. We also demonstrated that short duration (~21 days) space flight does not significantly alter the antibody repertoire (Chapter 5). The work culminates in an AOS study to assess changes to the B-cell immunoglobulin repertoire after vaccination with TT and/or CpG. The results show that changes to V-, D-, and J-gene segment usage occur after antigen challenge with AOS causing decreased class switching and frequency of plasma cells. Tetanus toxoid challenge decreased multiple gene segment usage and CpG administration increased isotype switching to the IgA constant region (Chapter 6).

Les mousses liquides sont des dispersions des bulles dans l'eau et elles sont largement utilisées dans un grand nombre de procédés technologiques et d’applications commerciales. Dans ma thèse, je me concentre sur les différents problèmes concernant les propriétés des mousses aqueuses et en particulier les écoulements gravitationnels dans les mousses.Les mousses contiennent une grande quantité d'interfaces couvertes par des molécules amphiphiles, et l'échange des tensioactifs entre l'interface et la phase volumique joue un rôle important pour la génération et la stabilité des mousses. Donc, mon premier projet a été d'étudier la dynamique d'adsorption de systèmes modèles aux interfaces air/eau. Les résultats obtenus nous ont aidés à comprendre comment l'adsorption lente des tensioactifs lors de la génération de la mousse peut influencer la mobilité des interfaces et changer le drainage de la mousse. Pour étudier les différents aspects de la physique de la mousse à l'échelle des bulles, des mousses pseudo-bidimensionnelles (des monocouches des bulles serrées entre deux plaques) sont largement utilisées. Dans ma thèse un modèle pour décrire la géométrie d'une mousse pseudo-bidimensionnelle a été introduit, cette description a été utilisée pour modéliser les conductivités électriques et hydrauliques de ces mousses. Dans certaines applications (par exemple, dans les industries du papier et de la peinture) la formation de la mousse peut causer de graves problèmes et des agents antimoussants appropriés sont utilisés. Dans ma thèse l'influence de la gravité sur l'efficacité antimoussante des gouttes d'huile de silicone a été étudiée expérimentalement en utilisant des vols paraboliques. Les résultats montrent que les particules antimoussantes ont besoin de la gravité pour être transportées d'une manière efficace, et la microgravité rend les antimousses très efficaces pratiquement inutiles. Etant initialement motivé par le transport des particules dans les mousses, j'ai également examiné la sédimentation des particules solides dans les capillaires de verre verticaux et inclinés. / Liquid foams are dispersions of bubbles in water and they are widely used in a large number of technical processes and commercial applications. In the present thesis I focus on different problems concerning properties of aqueous foams and especially gravity-driven flows in foams. Foams contain a large quantity of interfaces covered by surfactant molecules and the surfactant exchange between bulk and interface plays a crucial role for foam generation and stability. So my first project was to study the adsorption dynamics of model surfactant systems at air/water interfaces. The obtained results helped us to understand how the slow surfactant adsorption during foam generation can influence the mobility of interfaces and change foam drainage. To study different aspects of foam physics at the bubble scale simplified quasi-2D foams (monolayers of bubbles squeezed between two plates) are widely used. In this thesis a model to describe the geometry of a quasi-2D foam was introduced, this description was used to model the electrical and flow conductivities of such foams. In some applications (for example, in the paper and paint industries) foam formation can cause serious problems and suitable antifoaming agents need to be used. In my thesis the influence of gravity on the antifoaming efficiency of silicone oil droplets has been experimentally studied using parabolic flights. The results show that antifoam particles need gravity to be efficiently transported, and microgravity can render highly efficient antifoam practically useless. Being initially motivated by particle transport in foams, I have also looked at the sedimentation of solid particles in vertical and inclined glass capillaries.

A drop tower is a device that produces a microgravity environment by allowing an experiment to free fall for a short period of time, usually less than 10 seconds. Certain types of drop towers are also capable of reproducing the gravitational conditions of other celestial bodies, such as Lunar and Martian gravity. Microgravity environments are often required for many different scientific experiments, such as experiments in material science, fluid dynamics, biological studies and many other fields. Microgravity environments are also often used as a specialized manufacturing method for certain materials. Components and systems that will be used in space or onboard sounding rockets can also be tested and verified using drop towers before launch. There is an ever-present need to conduct experiments in a microgravity environment and thus highlights the importance and relevance of drop towers in research and design verification. Other microgravity facilities such as sounding rockets, parabolic flights and orbital spacecraft typically provide longer microgravity durations, however, come at a considerable cost. This highlights the need for drop towers that are cost-effective as a desirable research device. This thesis consists of a comprehensive, systematic literature review to determine industry standards and the current state of the art in the world of drop towers. The different potential mechanical designs of a drop tower are then analyzed and trade-offs are completed. The most suitable design, that could feasibly be built at Luleå University of Technology (LTU)’s space campus, is chosen and presented later in this thesis. The safety of the drop tower was of utmost concern when deciding on the most suitable design as well as when completing the mechanical design of the drop tower. The slider is a major component of a drop tower, it houses the experiment and is a critical component in determining the achievable microgravity quality. The slider design was also analyzed with a trade-off analysis of the potential existing designs, with the most feasible design being chosen. The drop tower is planned to be installed in the LTU Spacecampus light garden which can accommodate a drop tower of approximately 13m in height. The mechanical design is verified using various Finite Element Analysis (FEA) simulations. The 14m planned and designed drop tower is a non-vacuum, guided design which would provide approximately 3 seconds of microgravity, 5.2 seconds of Martian simulated gravity and 7.8 seconds of Lunar simulated gravity. The drop tower has been designed to accommodate projects that are part of the REXUS program. The towers' considerable size and ease of use would make it suitable for many research institutions and many potential scientific studies.

A deep space concept vehicle created from a core stage barrel section of the Space Launch System rocket has been designed by the National Aeronautics and Space Administration for use in future manned Mars missions. The spacecraft, known as the Space Launch System-Derived Habitat, features a dedicated space for exercise equipment. A human factors assessment was performed to determine whether or not the exercise area has adequate volume for multiple microgravity exercise machines to be used by multiple crew members simultaneously. It was determined that in its current design the exercise area does not have adequate volume to house the machines required for bone and muscle maintenance as required for long-duration spaceflight missions. It was recommended that the volume either be vastly expanded or dissolved entirely in favor of multiple, smaller exercise volumes that could each house one machine.

No description available.

No description available.

The rotating wall vessel (RWV) bioreactor is a well-established cell culture device for the simulation of microgravity for suspension cells and the generation of spheroids and organoids. The key to the success of these systems is the generation of a delicately maintained fluid dynamics system which induces a solid body rotation capable of suspending cells and other particles in a gentle, low-shear environment. Despite the unique capabilities of these systems, the inherently delicate nature of their fluid dynamics makes the RWV prone to multiple failure modes. One of the most frequently occurring, difficult to avoid, and deleterious modes of failure is the formation of bubbles. The appearance of even a small bubble in an RWV disrupts the crucial laminar flow shells present in the RWV, inducing a high-shear environment incapable of maintaining microgravity or producing true spheroids. The difficulty of eliminating bubbles from the RWV substantially increases the learning curve and subsequent barrier-to-entry for the use of this technology. The objective of this study is to create a novel RWV design capable of eliminating the bubble formation failure mode and to demonstrate the design’s efficacy. The tested hypothesis is: “The addition of a channel capable of segregating bubbles from the fluid body of the RWV will protect its crucial fluid dynamics system while enabling the growth of consistently sized and properly formed cell spheroids, improving ease of use of the RWV and decreasing experimental failure.” / Bioengineering

Yes / The application of omics to study Caenorhabditis elegans (C. elegans) in the context of spaceflight is increasing, illuminating the wide-ranging biological impacts of spaceflight on physiology. In this review, we highlight the application of omics, including transcriptomics, genomics, proteomics, multi-omics, and integrated omics in the study of spaceflown C. elegans, and discuss the impact, use, and future direction of this branch of research. We highlight the variety of molecular alterations that occur in response to spaceflight, most notably changes in metabolic and neuromuscular gene regulation. These transcriptional features are reproducible and evident across many spaceflown species (e.g., mice and astronauts), supporting the use of C. elegans as a model organism to study spaceflight physiology with translational capital. Integrating tissue-specific, spatial, and multi-omics approaches, which quantitatively link molecular responses to phenotypic adaptations, will facilitate the identification of candidate regulatory molecules for therapeutic intervention and thus represents the next frontiers in C. elegans space omics research.

In recent years, space exploration has been driving studies that enable sustained human presence in space. In such studies, fluidics relating to biology have become important. Fluids in biological systems span from large-scale flows relevant to circulatory, digestion, and pulmonary systems, but also involve many micro-scale porous flows. Hence, space exploration is driving a novel need to characterize fluidics in microscales in microgravity conditions. In this work, we study the porous flow network within bones that stimulates cellular growth and has the potential to relate to osteoporosis (including driving osteoporosis in astronauts). To study this effect, computational fluid dynamics (CFD) simulations are performed on a microfluidic device with a hexagon structure and compared to experimental results in both normal gravity (1g) and microgravity (0g) via Blue Origin's New Shepard Vehicle (NS-23 attempt and NS-24 launch). CFD results have been created to predict the transport character of nutrients in the bones. These insights have the potential to lead to preventative measures for osteoporosis in astronauts.