From the main sequence onwards, stars of intermediate masses (1-8 Solar masses) eject a large portion of their mass with rates as high as 0.0001 Solar masses per year during their transition through the Asymptotical Giant Branch (AGB) stage. The outflows are shaped by the same mechanisms that shape the ejecta, which in turn appear to depart from spherical symmetry as early as the AGB stage. The ejecta are then evolving into asymmetrical structures. Stars like that are giant factories of dust, responsible for the enrichment of their surrounding Galactic medium in metals heavier than helium. Depending on their abundances during the AGB stage, the stars are either oxygen-rich or carbon-rich, and as such, the dust produced in their atmospheres is either O-rich or C-rich. The chemical composition of the ejecta, indicates the stellar chemistry at the moment of ejection. The disruption of the spherical symmetry of the mass loss can be caused by fast rotation, stellar magnetic fields or binarity, the latter being the most efficient and favourable mechanism. Such mechanisms can lead to the creation of circumstellar, equatorial, dusty structures, like discs, torii or spirals. Due to their small relative sizes, compared to their surrounding nebulae, they can be studied at best with the use of infrared interferometric techniques. We report the discovery of three such structures in sources at three different evolutionary stages, respectively, with the use of single- and multi-aperture interferometry. In the C-rich AGB star V Hya we imaged via aperture masking in the near-infrared, a complex and possibly orbiting structure, which is embedded within the star's molecular torus. Our MIDI observations in the mid-infrared have revealed, a silicate disc within the symbiotic nebula M2-9 that is currently being shaped by the central binary system within its core, and a C-rich disc-like structure in the born-again star Sakurai's Object, that is also aligned to an asymmetry found in its surrounding planetary nebula. Finally, we compare the properties of the structures found here with those found in the literature in order to establish a relation between late stellar evolution and the existence of dusty structures.

Dust and gas in protoplanetary disks are the building blocks of planets. In this thesis, we study the dynamics of the gas and dust, which are crucial for the planet formation theory, using observational and numerical approaches. The observational part contains the case study of a rare circumtriple disk around the GW Ori hierarchical triple system. We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.3 mm dust continuum and 12CO J = 2-1 molecular gas emission of the disk. For the first time, we identify three dust rings in the GW Ori disk at ~46, 188, and 338 au, with the outermost ring being the largest dust ring ever found in protoplanetary disks. We use visibility modeling of the dust continuum and kinematics modeling of CO lines to show that the disk has misaligned parts, and the innermost dust ring is eccentric. We interpret these substructures as evidence of ongoing dynamical interactions between the triple stars and the circumtriple disk. In the numerical part, we study whether or not dust around gas gaps opened by planets can remain settled by performing three-dimensional, dust-plus-gas simulations of protoplanetary disks with an embedded planet. We find planets that open gas gaps 'puff up' small, sub-mm-sized grains at the gap edges, where the dust scale-height can reach 80% of the gas scale-height. We attribute this dust 'puff-up' to the planet-induced meridional gas flows previously identified by Fung and Chiang. We thus emphasize the importance of explicit 3D simulations to obtain the vertical distribution of sub-mm-sized grains around planet gaps. We caution that the gas-gap-opening planet interpretation of well-defined dust rings is only self-consistent with large grains exceeding mm in size. / Graduate

No description available.

Atmospheric mineral dust has a large impact on the earth’s radiation balance and climate. The radiative effects of mineral dust depend on factors including, particle size, shape, and composition which can all be extremely complex. Mineral dust particles are typically irregular in shape and can include sharp edges, voids, and fine scale surface roughness. Particle shape can also depend on the type of mineral and can vary as a function of particle size. In addition, atmospheric mineral dust is a complex mixture of different minerals as well as other, possibly organic, components that have been mixed in while these particles are suspended in the atmosphere. Aerosol optical properties are investigated in this work, including studies of the effect of particle size, shape, and composition on the infrared (IR) extinction and visible scattering properties in order to achieve more accurate modeling methods. Studies of particle shape effects on dust optical properties for single component mineral samples of silicate clay and diatomaceous earth are carried out here first. Experimental measurements are modeled using T-matrix theory in a uniform spheroid approximation. Previous efforts to simulate the measured optical properties of silicate clay, using models that assumed particle shape was independent of particle size, have achieved only limited success. However, a model which accounts for a correlation between particle size and shape for the silicate clays offers a large improvement over earlier modeling approaches. Diatomaceous earth is also studied as an example of a single component mineral dust aerosol with extreme particle shapes. A particle shape distribution, determined by fitting the experimental IR extinction data, used as a basis for modeling the visible light scattering properties. While the visible simulations show only modestly good agreement with the scattering data, the fits are generally better than those obtained using more commonly invoked particle shape distributions. The next goal of this work is to investigate if modeling methods developed in the studies of single mineral components can be generalized to predict the optical properties of more authentic aerosol samples which are complex mixtures of different minerals. Samples of Saharan sand, Iowa loess, and Arizona road dust are used here as test cases. T-matrix based simulations of the authentic samples, using measured particle size distributions, empirical mineralogies, and a priori particle shape models for each mineral component are directly compared with the measured IR extinction spectra and visible scattering profiles. This modeling approach offers a significant improvement over more commonly applied models that ignore variations in particle shape with size or mineralogy and include only a moderate range of shape parameters. Mineral dust samples processed with organic acids and humic material are also studied in order to explore how the optical properties of dust can change after being aged in the atmosphere. Processed samples include quartz mixed with humic material, and calcite reacted with acetic and oxalic acid. Clear differences in the light scattering properties are observed for all three processed mineral dust samples when compared to the unprocessed mineral dust or organic salt products. These interactions result in both internal and external mixtures depending on the sample. In addition, the presence of these organic materials can alter the mineral dust particle shape. Overall, however, these results demonstrate the need to account for the effects of atmospheric aging of mineral dust on aerosol optical properties. Particle shape can also affect the aerodynamic properties of mineral dust aerosol. In order to account for these effects, the dynamic shape factor is used to give a measure of particle asphericity. Dynamic shape factors of quartz are measured by mass and mobility selecting particles and measuring their vacuum aerodynamic diameter. From this, dynamic shape factors in both the transition and vacuum regime can be derived. The measured dynamic shape factors of quartz agree quite well with the spheroidal shape distributions derived through studies of the optical properties.

In laboratory experiments, I study strongly-coupled dusty plasma levitated in a glow-discharge plasma. Dusty plasma is an arrangement of small dust particles in a plasma background of electrons, ions, and neutral gas. The dust particles are negatively charged because they collect electrons and ions from the background plasma. Depending on the experimental setup, the plasma's electric field can help to balance the dust particles against gravity. The high dust charge causes dust particles to repel each other, while confinement forces prevent their escape. The dust particles cannot easily move past one another, and instead organize themselves into highly-ordered structures. The neutral gas also plays a key role in these experiments. Depending on the relative motion between gas and dust particles, the neutral gas can either impede dust motion or it can drive the dust into motion. In this thesis, I report the findings of three separate experiments. In the first experiment, I use a spherically-shaped dusty plasma (Yukawa ball) as an indicator of a flow of neutral gas, called thermal creep flow. In the second and third experiments, I study naturally occurring dust-density waves, which propagate within the volume of a dusty plasma that has many horizontal layers. In Ch.2 of this thesis, I study thermal creep flow (TCF), which is a flow of gas driven by a temperature gradient along a solid boundary. Stripes on a glass box are heated by laser beam absorption, leading to both TCF and a thermophoretic force. A stirring motion of the dust particle suspension is observed. By eliminating all other explanations for this motion, I conclude that TCF at the boundary couples by drag to the bulk gas, causing the bulk gas to flow, thereby stirring the suspension of dust particles. This result provides an experimental verification that TCF in the slip-flow regime causes steady-state gas flow in a confined volume. In Ch.3, I observe the growth of a naturally occurring dust-density wave (DDW) using high-speed imaging. This low-frequency wave (∼ 25 Hz) grows in amplitude as it propagates downward through a dusty plasma. I measure the wave's linear growth rate using a phase-sensitive analysis method. For the conditions studied here, the growth rate increases as gas pressure decreases. At a critical gas pressure that I observe, a balance between an ion-flow instability and dissipation by neutral gas drag determines a threshold for wave propagation. A linear dispersion relation is derived, taking into account effects of strong coupling, to compare to the experiment. In Ch.4, I observe the development of nonlinearity in the naturally occurring dust-density wave by measuring harmonics of the fundamental. Using high-speed imaging, I measure amplitudes, wave numbers and growth rates for the fundamental and its harmonics. The amplitudes of the harmonics exhibit a strong exponential increase with diminishing gas pressure, and they saturate at lower gas pressures. My measurements show that the wave numbers and growth rates of harmonics are near integer multiples of the fundamental.

L’étude en laboratoire de matériaux extraterrestres provenant d’objets ayant peu ou pas évolué depuis leur formation il y a environ 4.6 milliards d’années, peut améliorer notre connaissance sur les débuts de notre système planétaire. Par ailleurs, la simulation en laboratoire de certains processus que ces matériaux sont susceptibles de subir au cours de leur histoire apporte également de précieuses informations pour l’interprétation des données issues des observations astronomiques ainsi que pour la compréhension de l’évolution des solides du Milieu Interstellaire jusqu’à leur incorporation dans des objets planétaires, objets incluant aussi toutes sortes de débris tels que les astéroÏdes, les comètes et toutes sortes de poussières accessibles à la collecte et/ou à l’observation.Au cours de cette thèse, l’analyse des matériaux organiques ainsi que des matériaux silicatés, jusqu’alors peu étudiés conjointement, dans les poussières stratosphériques d’origine cosmique, révèle une corrélation entre la minéralogie des grains et la longueur des chaînes carbonées. Ce lien ne semble pas le fruit de processus à la surface des corps parents des grains mais semble plutôt tracer des processus pré-accrétionnels. La conservation de composants peu altérés sur les corps parents dans les matériaux extraterrestres est encore une fois confirmée par la découverte, au cours de cette thèse, d’inclusions dans la météorite carbonée « Paris » dont les spectres infrarouges sont très similaires à ceux des composés carbonés observés dans le Milieu Interstellaire. L’étude de grains cométaires issus de la mission spatiale Stardust a montré, contrairement à l’idée que les comètes soient composées uniquement de matériaux primitifs puisque conservés dans un réservoir froid, que celles-ci contiennent aussi un certain nombre de matériaux formés à haute température, confirmant alors de précédentes analyses d’échantillons de Stardust et impliquant des échanges de matériaux à grande échelle radiale dans le jeune Système solaire.La deuxième partie de ce travail, consacrée à l’étude d’analogues de matière extraterrestre, porte sur le rôle qu’ont pu jouer les matériaux à partir desquels les planètes telluriques se sont formées dans l’apport de l’eau sur la Terre dans le cadre du scénario dit de « wet accretion ». Les expériences effectuées au cours de cette thèse visant à simuler les interactions entre silicates et vapeur d’eau ont montré que ces matériaux permettent de stocker d’importantes quantités d’eau à leur surface par adsorption des molécules de la phase gazeuse. / Laboratory analyses performed on extraterrestrial materials originating from primitive bodies of our Solar System, that are bodies known to have suffered low alteration since their formation 4.6 billion years ago, can improve our knowledge on processes that have occurred in the early phase of our planetary system. Furthermore, laboratory simulations of some processes that these materials are likely to suffer during their life cycle also bring precious indications for interpreting observational data as well as for understanding the evolution of solids from the Interstellar Medium to their incorporation into planetary bodies, these latter including asteroids, comets and all kinds of dust that may be observed and/or collected back to Earth.During this thesis, the analysis of silicate as well as organic materials, which have not been much studied jointly so far, in stratospheric particles of cosmic origin, reveals a correlation between the mineralogy of the grains and the lengths of the chains of their carbonaceous component. This link does not seem to be due to parent body processing but rather to trace pre-accretionnal processes. The preservation of pristine components in extraterrestrial materials slightly altered on their parent bodies is again confirmed by the discovery in this work, of inclusions in the “Paris” carbonaceous chondrite whose infrared spectra are similar to the interstellar carbonaceous species. The study of cometary grains from the Stardust space mission showed, unlike the common idea that comets should be composed only of primitive materials since they reside in a cold reservoir, that comets do also contain a number of materials formed at high temperature, thus confirming results from previous studies of Stardust samples and implying large-scale radial mixing of materials in the young Solar system disk.The second part of my work, dedicated to experiments on primitive extraterrestrial amorphous silicates analogs, is aimed to study the role that materials from which Earth has accreted could have played in its water budget in the frame of the “wet accretion” scenario. The experiments performed along this thesis simulating interactions between silicates and water vapor, showed that silicates allow the storage of large quantities of water by adsorption onto their surface of molecules directly from the gas phase.

Atmospheric aerosols have been studied in great depth in regards to its metrological and chemical characterizations. Covering about 33% of the planet, the Global Dust Belt is the major source of wind-blown dust. Airborne aerosols play important roles in the Earth systems, impacting the marine and terrestrial ecosystems, human and organismal health. Aerosolized dust can carry a diverse range of microorganisms that may be transported across large distances. If surviving the transport, influence, as vectors supporting microbial populations or as pathogens to other organisms, the recipient ecosystems where they may be delivered through dry and wet depositions. Located in the middle of the global dust belt area, the Red Sea receives about 1.2 Mt of emitted dust particles per storm and a total of 6 Mt dust deposition from the annual 5-6 storm events, which may contain important loads of microorganisms. This dissertation characterizes the taxonomical compositions of airborne prokaryotes and micro-eukaryotes and their transport history in the dust-associated microbiome, and the functional profile of the airborne microorganisms. The samples required to achieve these goals were collected with a high-volume dust collector over the Red Sea from the coastal and offshore regions over two years. In addition, microbial communities sampled from the surface Red Sea water were used to establish the possible relationship, suggesting an exchange, between the airborne microbial communities and those in the Red Sea. Since relying on culture5 based analyses would take no notice of unculturable microorganism, culture-independent techniques were followed to detect the vast majority of the biological particles on the sampled air filters. However, large volumes of air should be collected due to the difficulty of acquiring enough genomic materials from the low density of airborne microorganisms for molecular assays. Sahara Deserts and deserts in the Arabian Peninsula represented the major sources of microbial inputs to the Red Sea atmosphere. Hence, a high number of allergens, plant and mammalian pathogens, human and animal parasites have been detected in airborne dust samples, which could be of concern. Functionally, dust-associated microbiome has exclusive lifestyle’s features that facilitate a resilient strategy to survive during airborne transportation, so-called “aeolian lifestyle.”

Aeolian dust exerts a notable influence on atmospheric and oceanic conditions and human health, particularly in arid and semi-arid regions like Saudi Arabia. Dust is often characterized by its mineral and chemical composition, but there is a microbiological component of natural aerosols which has received comparatively little attention. Moreover, the amount of materials suspended in the atmosphere is highly variable from day to day. Thus, knowing the loads of dust and suspended microbes and its variability over the year is essential to understand the possible effects of dust on the Red Sea ecosystem. Here, we present the first estimates of dust and microbial loads at a coastal side on the Red Sea over a two-year period supplemented with information from dust samples collected along the Red Sea in offshore water and their variability. Weekly average dust loads ranged from 4.63 to 646.11 μg m-3, while the abundance of airborne prokaryotic cells and viral particles ranged from 31,457 to 608,333 cells m-3 and from 69,615.5 to 3,104,758 particles m-3, respectively. These are the first estimates of airborne microbial abundance that we are aware of in this region. The large number of dust particles and suspended microbes found in the air indicates that airborne microbes may have a large impact on our health and that of the Red Sea ecosystem.

The work is devoted to the influence of dust particles on the operation of rotating machines with sliding contact. In the work are described and characterized dust particles from environment of selected machines. Their influence on sliding contact and influence on the insulation system of these machines is investigated.

No description available.