Dissertations / Theses on the topic 'Dust growth'
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Flanagan, Timothy McGuire. "Observations of thermal creep gas flow and dust-density waves in dusty plasma experiments." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/802.
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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.
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Güttler, Carsten [Verfasser], and Jürgen [Akademischer Betreuer] Blum. "From Dust to Planets: Dust Aggregation in the Post-Fractal Growth Regime / Carsten Güttler ; Betreuer: Jürgen Blum." Braunschweig : Technische Universität Braunschweig, 2009. http://d-nb.info/1175829420/34.
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Mlitan, Abdulmajeed Bashir. "Effects of cement dust and its constituents on fungal growth." Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.601751.
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Environmental pollution by cement is a serious problem and its effects on humans and plants have warranted careful attention in Libya in recent years as well as in the rest of the world, whereas the effects on fungi have not been investigated enough. This research aimed to investigate effects of cement dust pollution on fungal populations and how cement dust influences fungal growth. Soils and leaves from a cement-dust-polluted area near the Alkomos cement factory in Libya were studied. The physiochemical characteristics of soils in the study area indicate a strong influence by cement dusts that have settled 011 the soil from the cement factory. Calcium content and pH were higher than in similar unpolluted soils in this region. The dominance of fungi of soil and leaves was lowest at 100 m from the factory and the evenness and diversity increased at this site compared to the control area and 250 m from the factory . Variability and diversity of fungi were greater in the Summer (dry season) than the winter (rainy season). Aspergillus, Penicillium, and Fusarium were the most prevalent fungi isolated from contaminated samples.
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Couedel, Lenaic Gael Herve Fabien. "Nanoparticle formation and dynamics in a complex (dusty) plasma: from the plasma ignition to the afterglow." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/4121.
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Complex (dusty) plasmas are a subject of growing interest. They areionized gases containing charged dust particles. In capacitively-coupled RF discharges, dust growth can occur naturally and two methods can be used to grow dust particles: chemically active plasmas or sputtering. The growth of dust particles in argon discharges by RF sputtering and the effect of dust particles on theplasma have been investigated from the plasma ignition to the afterglow. It was shown that plasma and discharge parameters are greatly affected by the dust particles. Furthermore, plasma instabilities can be triggered by the presence of the dust particles. These instabilities can be due to dust particle growth or they can be instabilities of a well established dust cloud filling the interelectrode space. When the discharge is switched off, the dust particles act like a sink for the charge carrier and consequently affect the plasma losses. It was shown that the dust particles do keep residual chargeswhich values are greatly affected by the diffusion of the charge carriers and especially the transition from ambipolar to free diffusion.
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Couedel, Lenaic Gael Herve Fabien. "Nanoparticle formation and dynamics in a complex (dusty) plasma: from the plasma ignition to the afterglow." University of Sydney, 2008. http://hdl.handle.net/2123/4121.
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Doctor of Philosophy(PhD)Complex (dusty) plasmas are a subject of growing interest. They areionized gases containing charged dust particles. In capacitively-coupled RF discharges, dust growth can occur naturally and two methods can be used to grow dust particles: chemically active plasmas or sputtering. The growth of dust particles in argon discharges by RF sputtering and the effect of dust particles on theplasma have been investigated from the plasma ignition to the afterglow. It was shown that plasma and discharge parameters are greatly affected by the dust particles. Furthermore, plasma instabilities can be triggered by the presence of the dust particles. These instabilities can be due to dust particle growth or they can be instabilities of a well established dust cloud filling the interelectrode space. When the discharge is switched off, the dust particles act like a sink for the charge carrier and consequently affect the plasma losses. It was shown that the dust particles do keep residual chargeswhich values are greatly affected by the diffusion of the charge carriers and especially the transition from ambipolar to free diffusion.
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CARPENTER, WILLIAM JOSEPH. "Dust Grain Growth and Disk Evolution of a Set of Young Stellar Objects." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204639846.
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Okuzumi, Satoshi. "Theoretical Modeling of the Charging and Structure Evolution of Dust Aggregates in Protoplanetary Disks : Possible Discovery of an Electrostatic Barrier Against Dust Growth." Kyoto University, 2010. http://hdl.handle.net/2433/120430.
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Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第15464号
人博第494号
新制||人||121(附属図書館)
21||人博||494(吉田南総合図書館)
27942
京都大学大学院人間・環境学研究科相関環境学専攻
(主査)教授 阪上 雅昭, 准教授 小木曽 哲, 准教授 木下 俊哉, 助教 野村 英子
学位規則第4条第1項該当
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Elam, Robert J. "The Effects of Coal Dust Particulates on Growth Performance and Photomorphogenic Responses of Brassica Rapa." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1511869210184817.
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Andes, Glenda Gilmore. "The Effect of Carpet Fiber on the Growth of Dermataphagiodes farniae in a Controlled Environment." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/36256.
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Mites are endemic and allergy to mite excreta and parts is one of the most common allergies. Health care practitioners have recommended the removal of carpets from homes of people with mite allergies. Little, if any, consideration is given to the fact that some persons may benefit directly from the presence of carpet in their homes. In the allergen and mite research literature, carpets are rarely described as having unique characteristics and are generally referred to as a generic entity. Carpets, however, do have unique characteristics that define their construction, appearance, wearability, and cleanability.
Seventy-two pieces of commercially available, residential flooring materials were inoculated with identical numbers of mites, Dermatophagiodes farinae, and placed in the Textiles Conditioning Lab at Virginia Tech. The mites and carpet pieces were maintained in the lab, under identical, environmentally controlled conditions for 6 weeks, then the mites were extracted and counted.
On the basis of the results of statistical tests run on the study data, the null hypothesis, that there is no difference between the numbers of mites grown on the different flooring conditions, was rejected. Statistically significant differences exist between the hard floor and the nylon carpet, between hard floor and olefin carpets, but no difference between hard floor and wool carpet.
Nylon was the carpet fiber that was most supportive of the growth of house dust mites, olefin was the second most supportive, and wool carpet and hard floor were similar in being the least supportive.Master of Science
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De, Necker Adele. "The development of a strategic plan for a company in the dust suppression industry / de Necker A." Thesis, North-West University, 2011. http://hdl.handle.net/10394/7377.
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The general aim of this study was to develop a strategic plan for a company in the dust
suppression industry. Currently there is no formal process documented or analysis done
within the company regarding strategic planning due to the company being founded,
extensive growth taking place year on year and the urgent need for the operations to be
established, in order for the company to start selling their products and services. The
study was conducted among a sample of 45 junior, middle and senior management
employees within this company.
The data collected from the participants were collected personally via interviews and a
strategic planning questionnaire and recorded electronically by the Statistical Consultation
Services at the North–West University and the data were analysed by means of the
Statistical Package for Social Sciences (SPSS V18). In addition to the structured
questionnaires, management was also interviewed to assess their views on the strategic
planning at the company.
The results and findings indicated that there was some strategic planning actions lacking
and that formal strategic planning that defines objectives and assessment of the various
situations within the company, are not properly performed. The author was however able
to evaluate and determine where the company is going over the next three years. The
study draws a number of conclusions and makes recommendations with regard to
strategic planning, one of which is that the company should follow a more structured and
formalised approach.Thesis (M.B.A.)--North-West University, Potchefstroom Campus, 2012.
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Lee, Yong Seob. "Investigation of the optical and cloud forming properties of pollution, biomass burning, and mineral dust aerosols." Texas A&M University, 2003. http://hdl.handle.net/1969.1/3947.
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This dissertation describes the use of measured aerosol size distributions and size-resolved hygroscopic growth to examine the physical and chemical properties of several particle classes. The primary objective of this work was to investigate the optical and cloud forming properties of a range of ambient aerosol types measured in a number of different locations. The tool used for most of these analyses is a differential mobility analyzer / tandem differential mobility analyzer (DMA / TDMA) system developed in our research group. To collect the data described in two of the chapters of this dissertation, an aircraft-based version of the DMA / TDMA was deployed to Japan and California. The data described in two other chapters were conveniently collected during a period when the aerosol of interest came to us. The unique aspect of this analysis is the use of these data to isolate the size distributions of distinct aerosol types in order to quantify their optical and cloud forming properties.
I used collected data during the Asian Aerosol Characterization Experiment (ACE-Asia) to examine the composition and homogeneity of a complex aerosol generated in the deserts and urban regions of China and other Asian countries. An
aircraft-based TDMA was used for the first time during this campaign to examine the size-resolved hygroscopic properties of the aerosol. The Asian Dust Above Monterey (ADAM-2003) study was designed both to evaluate the degree to which models can predict the long-range transport of Asian dust, and to examine the physical and optical properties of that aged dust upon reaching the California coast. Aerosol size distributions and hygroscopic growth were measured in College Station, Texas to investigate the cloud nucleating and optical properties of a biomass burning aerosol generated from fires on the Yucatan Peninsula. Measured aerosol size distributions and size-resolved hygroscopicity and volatility were used to infer critical supersaturation distributions of the distinct particle types that were observed during this period. The predicted cloud condensation nuclei concentrations were used in a cloud model to determine the impact of the different aerosol types on the expected cloud droplet concentration. RH-dependent aerosol extinction coefficients were also calculated.
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Boehler, Yann. "Étude du grossissement et de la distribution spatiale des grains de poussière dans les disques protoplanétaires." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14146/document.
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Les étoiles, durant les premiers millions d’années de leur existence, sont entourées d’un disque composé à 99% de gaz et à 1 % de poussière. La poussière est initialement sous forme de grains de taille sub-micrométrique mais évolue jusqu’à pouvoir former les planètes. Grâce à l’interféromètre du plateau de Bure, avec lequel nous avons observé aux longueurs d’onde millimétrique, l’évolution temporelle ainsi que la distribution radiale des grains de poussière a pu être mise en évidence sur de nombreux disques. Par ailleurs, l’important gain en résolution et sensibilité d’ALMA, un nouvel interféromètre très performant basé au Chili, a nécessité l’amélioration de notre code de transfert radiatif afin de déterminer si et comment il allait être possible d’observer la sédimentation de la poussière, étape préalable à la formation des planétésimauxThe stars, during the first millions years of their existence, are surrounded by a protoplanetary disk composed of99 % of gas and of 1 % of dust. The dust is initially under the form of sub-micrometric grains but evolves to likelyform planets. Thanks to the Plateau de Bure interferometer, with whom we observed at the millimeter wavelengths, the temporal evolution as well the radial distribution of the dust grains has been bringing to light in several disks.In addition, the important gain in resolution and in sensibility of ALMA, a new interferometer based in Chili, has required the improvement of our transfert radiativ code in order to determine if and how it will be possible to observe the dust settling, preliminary step for the formation of planetesimals
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Yella, Lakshmi. "The Influence of Temperature on Population Growth and Allergen Production in Cultured House Dust Mites – Dermatophagoides pteronyssinus and Dermatophagoides farinae." Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1260772254.
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Hassanpouryousefi, Sina. "Modeling Electrospun Fibrous Materials." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6109.
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Electrospinning has been the focus of countless studies for the past decades for applications, including but not limited to, filtration, tissue engineering, and catalysis. Electrospinning is a one-step process for producing nano- and/or micro-fibrous materials with diameters ranging typically from 50 to 5000 nm. The simulation algorithm presented here is based on a novel mass-spring-damper (MSD) approach devised to incorporate the mechanical properties of the fibers in predicting the formation and morphology of the electrospun fibers as they travel from the needle toward the collector, and as they deposit on the substrate. This work is the first to develop a physics-based (in contrast to the previously-developed geometry-based) computational model to generate 3-D virtual geometries that realistically resemble the microstructure of an electrospun fibrous material with embedded particles, and to report on the filtration performance of the resulting composite media.
In addition, this work presents a detailed analysis on the effects of electrospinning conditions on the microstructural properties (i.e. fiber diameter, thickness, and porosity) of polystyrene and polycaprolactone fibrous materials. For instance, it was observed that porosity of a PS electrospun material increases with increasing the needle-to-collector distance, or reducing the concentration of PS solution. The computational tool developed in this work allows one to study the effects of electrospinning parameters such as voltage, needle-to-collector distance (NCD), or polymer concentration, on thickness and porosity of the resulting fibrous materials. Using our MSD formulations, a new approach is also developed to model formation and growth of dust-cakes comprised of non-overlapping non-spherical particles, for the first time. This new simulation approach can be used to study the morphology of a dust-cake and how it impacts, for instance, the filtration efficiency of a dust-loaded filter, among many other applications.
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Nabeel, Muhammad. "A study of micro-particles in the dust and melt at different stages of iron and steelmaking." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-196805.
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The dust particles generated due to mechanical wear of iron ore pellets and clusters formed in molten stainless steel alloyed with rare earth metals (REM) are considered in this study. Firstly, the influence of the characteristics of iron ore pellets, applied load on a pellet bed and partial reduction of the pellets on the size distribution of the generated dust was investigated. Secondly, REM clusters are investigated to evaluate the size distribution of the clusters. Also, an extreme value distribution (EVD) analysis has been applied for the observed REM clusters. The large sized pellets showed 10-20% higher wear rate than small sized pellets during wear in a planetary mill. Moreover, an increase of ~67% was observed in the friction and dust generation in the pellet bed as the applied load increased from 1 to 3 kg. Also, it was observed that a higher friction in the pellet bed can lead to an increased amount of airborne particles. The mechanical wear experiments of pellets reduced at 500 °C (P500) and 850 °C (P850) showed that P500 pellets exhibit ~16-35% higher wear rate than unreduced pellets. For the P850 pellets, the wear is inhibited by formation of a metallic layer at the outer surface of the pellets. The mechanism of dust generation has been explained using the obtained results. A reliable cluster size distribution of REM clusters was obtained by improving the observation method and it was used to explicate the formation and growth mechanism of REM clusters. The results show that the growth of clusters is governed by different types of collisions depending on the size of the clusters. For EVD analysis three different size parameters were considered. Moreover, using the maximum length of clusters results in a better correlation of EVD regression lines compared to other size parameters. Moreover, a comparison of predicted and observed maximum lengths of clusters showed that further work is required for the application of EVD analyses for REM clusters.Studien fokuserar på två olika typer av mikropartiklar som är valda från olika delar av järn- och ståltillverkningsprocessen. Dessa partiklar är dels stoft som genereras på grund av mekanisk nötning av partiklar och dels klusters som bildas i flytande rostfria stål legerade med sällsynta jordartsmetaller (REM). Inledningsvis så undersöktes inverkan av tre faktorer på storleksfördelningen hos stoft som bildas vid hantering av järnoxidpellets. De undersökta faktorerna inkluderade karakteristiken hos järnoxidpellets, det applicerade trycket på pelletsbädden och den partiella reduktionen av järnoxidpellets. Därefter så utfördes tredimensionella undersökningar av REM kluster som extraherats med hjälp av elektrolytisk extraction för att bestämma storleksfördelningen hos klustren. Dessutom så utfördes en extremvärdesdistribution (EVD) studie för de studerade klustren. En planetkvarn användes för att undersöka inverkan of karakeristiken hos pellets på stoftbildningen. Resultaten visade att storleken på pellets kan påverka nötningshastigheten under dessa försöksförhållanden. Pellets som hade en större storlek (13.5< Deq <15.0 mm) uppvisade en 10 till 20% högre nötningshastighet i jämförelse med mindre pellets (9.5< Deq <12.5 mm). Baserat på analyserna av stoftet som genererades under nötningsexperimenten så konstaterades att nötningsmekanismerna för dessa pellets var abrasions- och kollisionsnötning. En pelletsbädd skapades för att möjliggöra studier av inverkan av ett applicerat tryck på stoftbildningen och friktionskrafterna i en pelletsbädd. Ett varierat tryck på mellan 1 till 3 kg applicerades på pelletsbädden. Resultaten visade att en ökning på ~67% av friktionskraften och stoftbildningen ägde rum när det applicerade trycket ökades från 1 till 3kg. Dessutom så visade resultaten att en högre friktionskraft i pelletsbädden kan resultera in en ökad mängd luftburna partiklar. Den mekaniska nötningen av pellets som reducerats vid 500 °C (P500) och 850 °C (P850) studerades också genom användande av en planetkvarn. Resultaten visade att P500 pellets uppvisade en ~ 16 till 35% högre nötningshastighet i jämförelse med oreducerade referenspellets. Resultaten för P850 pellets visade att den mekaniska nötningen motverkades genom bildningen av ett metalliskt skikt på den yttre delen av pelletsen. Resultaten visade också att stoftet som bildats pga mekanisk nötning av reducerade pellets innehöll 3 till 6 gånger mer grova partiklar (>20µm) i jämförelse med stoft som bildats från oreducerade pellets. Slutligen så diskuterades hur dessa resultat kan relateras till industriella förhållanden med avseende på mekanismerna som är involverade i den mekaniska nötningen av pellets samt med avseende på relationen mellan hastigheten av de utgående gaserna och storlken och morfologin hos stoftpartiklarna. Klusters innehållande REM-oxider som extraherats från en 253MA rostfri stålsort undersöktes med användande av en tredimensionell teknik. En trovärdig storleksfördelning av klusters (CSD) erhölls genom att förbättra undersökningsmetoden och denna användes för att studera bildningen och tillväxten av REM oxider. Dessutom så användes cirkularitetsfaktorn hos klusters för att dela in klustren i två olika grupper, vilka bildas och tillväxer enligt olika mekanismer. Resultaten visade också att tillväxten av klusters gynnas av olika typer av kollisioner som beror av av storleken på klusters. För REM-klusters så drogs slutsatsen att turbulenta kollisioner är den huvudsakliga mekanismen som påverkar tillväxten. Avhandlingen behandlar även problemet om hur det är möjligt att hantera synfält där det inte förekommer kluster vid en extremvärdesdistribution (EVD) analys. Tre olika parametrar undersöktes i EVD analysen. Resultaten visar att om den maximala längden på kluster (LC) används i analysen så erhålls den bästa korrelationen gällande regressionslinjen för en EVD analys. Specifikt så var R2 värdet upp till 0.9876 i jämförelse med de andra storleksparametrarna som har värden i intervallet 0.9656 – 0.9774. Slutligen så visar resultaten från en jämförelse mellan beräknade och observerade maximala klusterlängder att EVD analyser för studier av REM kluster behöver undersökas ytterligare i framtiden.
QC 20161128
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Sauter, Jürgen [Verfasser]. "Observing dust grain growth and sedimentation in circumstellar discs : interpretations and predictions of their observable quantities in a multi-wavelength approach / Jürgen Sauter." Kiel : Universitätsbibliothek Kiel, 2011. http://d-nb.info/1020496576/34.
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Poola, Swetha Avula. "INFLUENCE OF DIET ON POPULATION GROWTH AND ALLERGEN PRODUCTION IN CULTURED HOUSE DUST MITES - DERMATOPHAGOIDES FARINAE AND DERMATOPHAGOIDES PTERONYSSINUS." Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1247665992.
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Li, Xuefeng. "Marine Iron Biogeochemistry Under a Changing Climate: Impact on the Phytoplankton and the Diazotroph Communities." Doctoral thesis, Universite Libre de Bruxelles, 2018. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/266850.
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Diatoms constitute a major group of phytoplankton, accounting for ~20% of the world’s primary production. Biological dinitrogen (N2) fixation by diazotrophic cyanobacteria has great biogeochemical implications in nitrogen (N) cycling, being the major source of new N input to the oceans and thereby contributing significantly to carbon (C) export production. It has been shown that iron (Fe) can be the limiting nutrient for phytoplankton growth, in particular, in the HNLC (High Nutrient Low Chlorophyll) regions. Iron plays thus an essential role in governing the marine primary productivity and the efficiency of biological carbon pump. Oceanic systems are undergoing continuous modifications at varying rates and magnitudes as a result of changing climate. The objective of our research is to evaluate the effects of global climate change processes (changing dust deposition, ocean acidification and sea-surface warming) on phytoplankton growth, biological N2 fixation, biogeochemical cycles, and the controlling role of Fe within these impacts. Laboratory culture experiments using a marine diatom Chaetoceros socialis were conducted at two temperatures (13 ℃ and 18 ℃) and two carbon dioxide partial pressures (pCO2, 400 µatm and 800 µatm). The present study clearly highlights the effect of ocean acidification on enhancing the release of Fe upon dust deposition. Our results also confirm that being a potential source of Fe, mineral dust provides in addition a readily utilizable source of macronutrients such as phosphorus (P) and silicon (Si). However, elevated atmospheric CO2 concentrations and ocean acidification may also have an adverse impact on diatom growth, causing a decrease in cell size and possible further changes in phytoplankton composition. Meanwhile, increasing temperature and ocean warming may lead to the reduction of diatom production as well as cell size, inducing poleward shifts in the biogeographic distribution of diatoms. Numerous factors can affect the extent of N2 fixation. A better understanding of the major environmental and nutrient controls governing this process is highly required. Iron and/or phosphorus are thought to be limiting factors in most oceanic regions. Special attention has been given to studying the effects of mineral dust deposition which is believed to promote N2 fixation as it increases the availability of both Fe and P. Three laboratory bioassays (+Fe, +P, +Dust) via incubation experiments were performed on Trichodesmium IMS101, an important contributor to marine N2 fixation. Each addition of Fe, P or desert dust was found to stimulate the growth and the N2 fixation activity of Trichodesmium IMS101. Several adaptive nutrient utilization strategies were observed, such as a Fe luxury uptake mechanism, a P-sparing effect and colony formation. In addition, during a field study in the temperate Northeast Atlantic Ocean using natural phytoplankton assemblages, N2 fixation was remarkably stimulated through the addition of dissolved Fe under low temperature and depleted P conditions, highlighting the critical role of Fe. At the time of this study, no Trichodesmium filaments were found in the region of investigation. The diazotrophic community was dominated by the unicellular cyanobacteria symbiont (prymnesiophyte-UCYN-A1) and heterotrophic diazotrophs, therefore suggesting that Fe could be the ultimate factor limiting N2 fixation of these smaller diazotrophs as well. Recently, the effects of ongoing climate change (ocean warming and acidification) on N2 fixation drew much attention, but various studies led to controversial conclusions. Semi-continuous dilution growth experiments were conducted on Trichodesmium IMS101 under future high pCO2 and warming seawater conditions (800 µatm and 28 °C) and compared to the present-day situations (400 µatm and 24 °C). The results indicate that higher pCO2 and therefore ocean acidification may be beneficial for Trichodesmium growth and N2 fixation. However, the present study suggests that Fe or P limitation in oligotrophic seawaters may offset the stimulation induced on Trichodesmium IMS101 due to ocean acidification. In contrast, ocean warming may not play an important role in Trichodesmium growth and N2 fixation with a 4 °C increase from 24 °C to 28 °C. Nevertheless, ocean warming was previously predicted to cause a shift in the geographical distribution of Trichodesmium toward higher latitudes, extending its niche to subtropical regions and potentially reducing its range in tropical ocean basins.Overall, the biological responses of the marine diatom Chaetoceros socialis and the N2-fixing cyanobacteria Trichodesmium IMS101 to several key climate change processes were presented and discussed in this study. These processes included dust deposition, and ocean acidification and warming, which were shown to have a significant impact on oceanic phytoplankton growth, cell size and primary productivity, biological N2 fixation, phytoplankton distribution and community composition. They would thus affect the C, N, P, Si and Fe biogeochemical cycles in various ways. Iron, as one of the most crucial micronutrients for marine phytoplankton, has in particular strong links to climate change and biogeochemical feedback mechanisms.Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Rigon, Laura. "Lights and shadows : multi-wavelength analysis of young stellar objects and their protoplanetary discs." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/8646.
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Stars form from the collapse of molecular clouds and evolve in an environment rich in gas and dust before becoming Main Sequence stars. During this phase, characterised by the presence of a protoplanetary disc, stars manifest changes in the structure and luminosity. This thesis performs a multi-wavelength analysis, from optical to mm range, on a sample of young stars (YSOs), mainly Classical T Tauri (CTTS). The purpose is to study optical and infrared variability and its relation with the protoplanetary disc. Longer wavelength, in the mm range, are used instead to investigate the evolution of the disc, in terms of dust growth. In optical, an F-test on a sample of 39 CTTS reveals that 67\% of the stars are variable. The variability, quantified through pooled sigma, is visible both in magnitude amplitudes and changes over time. Time series analysis applied on the more variable stars finds the presence of quasi periodicity, with periods longer than two weeks, interpreted either as eclipsing material in the disc happening on a non-regular basis, or as a consequence of star-disc interaction via magnetic field lines. The variability of YSOs is confirmed also in infrared, even if with lower amplitude. No strong correlations are found between optical and infrared variability, which implies a different cause or a time shift in the two events. By using a toy model to explore their origin, I find that infrared variations are likely to stem from emissions in the inner disc. The evolution of discs in terms of dust growth is confirmed in most discs by the analysis of the slope of the spectral energy distribution (SED), after correcting for wind emission and optical depth effects. However, the comparison with a radiative transfer model highlights that a number of disc parameters, in particular disc masses and temperature, dust size distribution and composition, can also affect the slope of the SED.
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Garcia, Anthony. "Évolution de la porosité des grains : une solution aux problèmes de formation planétaire ?" Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1142/document.
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Dans les disques protoplanétaires, les grains micrométriques croissent jusqu'à atteindre des tailles de planétésimaux avant de finalement former des planètes. Cependant,des études dynamiques ont montré qu'une fois que les grains atteignent une taille critique, ils dérivent rapidement vers l'étoile et y sont accrétés. Ce problème est connu comme la barrière de dérive radiale. De plus, des expériences en laboratoire ont montré que les grains peuvent fragmenter ou rebondir et ainsi arrêter la croissance avant les tailles kilométriques.Afin de passer outre ces barrières, plusieurs méthodes ont été proposés comme les pièges à particules (dans les vortex ou les sillons planétaires) qui demandent des évolutions dynamiques à grande échelle. Dans ce travail, nous choisissons d'étudier les propriétés intrinsèques de la poussière pendant leur croissance et plus particulièrement leur porosité.Nous développons un modèle d'évolution de la porosité pendant la croissance en fonction de la masse des grains pour plusieurs régimes d'expansion/compression (Kataoka et al. 2013, Okuzumi et al. 2012) et l'implémentons dans notre code SPH bifluide (Barrière-Fouchet et al. 2005). Nous trouvons que la croissance des grains poreux est accélérée en comparaison aux grains compacts et leur taille peut atteindre plusieurs kilomètres. De surcroît,la dérive est légèrement ralentie pour les grains poreux qui peuvent croître jusqu'à de plus grandes tailles avant de commencer à dériver vers l'étoile. Nous constatons aussi que les grains des régions externes du disque grossissent plus que quand l'effet de la porosité est négligé. Ces deux mécanismes peuvent aider les grains à outrepasser la barrière de dérive radiale, notamment en passant dans le régime de traînée de Stokes, et ainsi former des planétésimaux.Nous étudions aussi l'effet de la fragmentation et du rebond sur le comportement des grains. En considérant un seuil de fragmentation constant, nous observons que la croissance de grains poreux est retardée un temps par la fragmentation mais qu'elle se poursuit vers de grandes tailles et par conséquent, permet de passer outre les problèmes dus à la fragmentation et à la dérive radiale. Cependant, les grains très poreux sont plus fragiles et peuvent se fragmenter plus facilement entraînant une accrétion massive des poussières dans l'étoile. De plus, nous montrons que les effets du rebond peuvent être négligés devant ceux de la fragmentation.Enfin, nous observons également que la taille des monomères et du paramètre de viscosité turbulente peut avoir une influence sur l'évolution de la porosité et donc de la poussière dans le disque.La porosité permet donc de favoriser la croissance des grains et accélérer le découplage des grains. Les grains très poreux peuvent être plus sensibles à la fragmentation.Cependant, les effets collectifs de la poussière couplés à la porosité peuvent aider les grains à outrepasser les barrières de formation planétaire. La barrière de rebond peut être négligée dans le cas de grains poreux devant les autres barrières. Enfin,l'intensité de la turbulence altère la croissance et ainsi le devenir de la poussière.La taille des monomères modifie le facteur de remplissage sans toutefois impacter le découplage des grains dans les parties internesIn protoplanetary discs, micron-sized grains should grow up to planetesimal sizes in order to ultimately form planets. However, dynamical studies show that once they reach a critical size, they drift rapidly into the accreting star. This is known as the radial-drift barrier. Moreover, laboratory experiments have shown that grains can fragment or bounce, stopping the growth towards planetesimal sizes.In order to overcome those barriers, several methods have been proposed such as particles traps (e.g. vortices or planet gaps) which all involve large-scale dynamics.In this work, we choose to investigate the intrinsic properties of the grains during their growth, in particular their porosity.We thus consider the growth of grains with variable porosity as a function of their mass in several regimes of compression/expansion (Kataoka et al. 2013, Okuzumiet al. 2012) and implement it in our 3D SPH two-fluid code (Barrière-Fouchetet al. 2005).We find that growth is accelerated for porous grains that can reach kilometersizes. On the other hand, drift is slightly slowed down for porous grains that can grow up to larger sizes before drifting towards the star. As a result, grains in the outer regions of the disc reach larger sizes than when porosity is neglected. Those two mechanisms can help grains overcome the radial-drift barrier and form planetesimals.The Stokes drag regime appears to play a substantial part in maintaining grains in the disc.Considering a constant fragmentation threshold, we also find out that growth is delayed because of fragmentation but reaching large sizes and thus overcoming problems due to fragmentation and radial drift is still possible. However, very fluffy grains are fragile and can be easily disrupted leading to a massive accretion of dust into the star. Moreover, we show that the effects due to dust bouncing can be neglected compared to fragmentation.Finally, we investigate the influence of the size of monomers and -parameter on the evolution of porosity and then dust in the disc.Dust growth is accelerated by porosity and thus promotes grains decoupling. Very fluffy grains are more affected by fragmentation. However, dust collective effects and porosity can help grains to overcome planet formation barriers. Besides,the bouncing barrier can be neglected in the case of porous dust compared to other barriers. Finally, the intensity of turbulence can alter the growth and so the outcome of dust. The size of monomers modifies the grain filling factor without impacting dust decoupling in the inner parts of the disc
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Clark, Jordan. "The role of PPAR ligands in collecting duct growth and apoptosis." Thesis, University of Ottawa (Canada), 2008. http://hdl.handle.net/10393/27671.
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The collecting duct (CD) has considerable expression of PPARdelta and PPARgamma. While their roles are unknown in the CD, in other cells they have been shown to regulate both growth and apoptosis. We thus investigated the hypothesis that PPARs reduce apoptotic responses in the mouse collecting duct IMCD-K2 and M-1 cells and that while PPARgamma has an inhibitory effect on cell growth, PPARdelta stimulates growth in these cells. This study characterized the growth and apoptotic responses in the collecting duct cells, M-1 and IMCD-K2, in response to the PPARdelta and PPARgamma ligands, GW501516 and troglitazone. The extent of apoptosis in IMCD-K2 and M-1 cells, induced by anisomycin, was only affected by troglitazone, which reduced the protein levels of cleaved caspase-3 in M-1 cells. GW501516 treatment increased DNA synthesis in IMCD-K2 cells, decreased DNA synthesis in M-1 cells, and decreased protein synthesis in both IMCD-K2 and M-1 cells. Additionally, troglitazone reduced DNA and protein synthesis in M-1 cells, and this effect was unaltered in the presence of the PPARgamma antagonist and ERK inhibitor. However, troglitazone treatment alone increased the levels of pERK. These results show PPAR ligands negatively regulate growth and apoptosis in CD cell lines, but more work is needed to ascertain the therapeutic potential of PPAR ligands in the prevention of CD injury.
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Falin, Rebecca A. "Acute Inhibition of the Epithelial Sodium Channel." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1190724697.
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Scott, Ryan 1981. "Investigating the natural history of human islet-derived duct-like structures transplanted subcutaneously into nude mice." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=112362.
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Islet plasticity has proven to be an important platform for the engineering of alternative islet tissue for transplantation. In vitro studies have shown the ability of islets to transdifferentiate into duct-like epithelial structures (DLS) thought to possess progenitor cells capable of replenishing damaged tissue within the pancreas. The aim of this study was to investigate the natural history of human derived duct-like epithelial structures transplanted into nude mice.Human islet derived duct-like structures from three cadaver pancreases were subcutaneously transplanted into 6-8 week old male HSD athymic nude-Foxn1 mice. Six mice were sacrificed at day 3, 7, 14 and 21 from each time period. DLS were also placed in matrigel for in-vitro control samples. DLS were processed for immunohistochemistry for endocrine markers, epithelial markers, cell death and proliferation markers, islet maturation markers and angiogenic factors.
Our results show that as DLS are transplanted, there is an increase in cell death and proliferation. This increase in cell death and proliferation causes an increase in PDX-1 expression as well as VEGF, an angiogenic factor. But over time, transplanted DLS do not show an increase in cell death and show a small decrease in cell proliferation from pre-transplanted DLS. At day 3 of engraftment, DLS show a significant expression of PDX-1. We see a small increase in endocrine tissue after 3 days of transplantation, then an increase in endocrine cell death, which returns the percentage of endocrine cells back to pre-transplantation levels at day 21. DLS were shown to express VEGF, and once transplanted into an initial hypoxic environment there is a substantial increase in expression, followed by a recruitment of microvessels. Although there is a dynamic change in expression of cell markers throughout engraftment, there is no significant change in DLS size, nuclei per DLS or cell morphology over time.
DLS have been shown to survive subcutaneous transplantation and possess an initial increase in cell proliferation leading to increases in PDX-1 and VEGF expression. Transplanted DLS have shown to possess significant angiogenic properties with the recruitment of microvessels into subcutaneous DLS grafts. Subcutaneous DLS transplantation could be used in combination with islet transplantation to alleviate current problems with islet transplantation such as islet cell death and insufficient blood supply.
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Siqueira, Orlando Hiroshi Kiono. "Efeito do tamoxifeno na fibrose, colágeno e expressão do transforming growth factor -B1, -B2 e -B3 na anastomose da via biliar principal deporcos." Universidade Federal Fluminense, 2017. https://app.uff.br/riuff/handle/1/5483.
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Universidade Federal Fluminense. Hospital Universitário Antônio Pdro
Introdução: A anastomose término-terminal no tratamento da lesão das vias biliares durante a colecistectomia laparoscópica tem sido associada à formação de estenose. O objetivo deste estudo foi investigar experimentalmente o efeito do tratamento oral com tamoxifeno (tmx) sobre a fibrose, o colágeno e o transforming growth factor TGF-β1, - β2 e - β3 na anastomose da via biliar principal de porcos. Métodos: Vinte e seis porcos foram divididos em três grupos [sham (n = 8), controle (n = 9) e tmx (n = 9)]. Os ductos biliares foram seccionados e anastomosados nos grupos controle e tmx. Tmx (40 mg / dia) foi administrado oralmente ao grupo tmx, e os animais foram eutanasiados após 60 dias. A fibrose foi analisada pela coloração com tricromo de Masson. Picrosirius red foi utilizado para quantificar o teor total de colágeno e a proporção de colágeno tipo I / III. A expressão de mRNA do TGF-β1, -β2 e - β3 foi quantificada usando a reação em cadeia da polimerase em tempo real (qRT-PCR). Resultados: Os grupos de controle e estudo apresentaram fibrose maior do que o grupo sham, e o grupo de estudo apresentou fibrose menor do que o grupo controle (p = 0,011). Os grupos controle e tmx apresentaram maior teor total de colágeno do que o grupo sham (p = 0,003) e não houve diferença significativa entre os grupos controle e tmx. A proporção de colágeno tipo I / III foi maior no grupo controle do que nos grupos sham e tmx (p = 0,015) e não houve diferença significativa entre os grupos sham e tmx. Não houve diferenças significativas na expressão de mRNA de TGF-β1, -β2 e -β3 entre os grupos (p> 0,05). Conclusões: Tmx diminuiu a fibrose e impediu a alteração na proporção de colágeno tipo I / III causada pelo procedimento.
Introduction: End-to-end anastomosis in the treatment of bile duct injury during laparoscopic cholecystectomy has been associated with the formation of stenosis. The aim of this study was to experimentally investigate the effect of oral treatment with tamoxifen (tmx) on fibrosis, collagen and transforming growth factor TGF-β1, - β2 and – β3 on anastomosis of the common bile duct in pigs. Methods: Twenty-six pigs were divided into three groups (sham (n = 8), control (n = 9) and tmx (n = 9)). The bile ducts were sectioned and anastomosed in the control and tmx groups. Tmx (40 mg / day) was administered orally to the tmx group, and the animals were euthanized after 60 days. Fibrosis was analyzed by Masson's trichrome staining. Picrosirius red was used to quantify the total collagen content and the proportion of collagen type I / III. Expression of TGF-β1, -β2 and -β3 mRNA was quantified using the real-time polymerase chain reaction (qRT-PCR). Results: The control and study groups presented higher fibrosis than the sham group, and the study group had lower fibrosis than the control group (p = 0.011). The control and tmx groups presented higher total collagen content than the sham group (p = 0.003) and there was no significant difference between the control and tmx groups. The proportion of type I / III collagen was higher in the control group than in the sham and tmx groups (p = 0.015) and there was no significant difference between the sham and tmx groups. There were no significant differences in TGF-β1, -β2 and -β3 mRNA expression between the groups (p> 0.05). Conclusions: Tmx decreased fibrosis and prevented the change in the proportion of collagen type I / III caused by the procedure.
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Hazrati, Ali. "The role of transforming growth factor-beta (TGF-) in the transdifferentiation of islets of Langerhans to duct-like epithelial structures /." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33773.
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The process of islet isolation destroys extracellular matrix and eliminates potentially important inter-cellular relationships. We have previously shown that isolated islets embedded in a type I collagen gel, in the presence of a defined medium, undergo a phenotypic switch to duct-like epithelial structures through a process known as transdifferentiation. The aim of this study was to characterize the specific effectors implicated in islet cell transdifferentiation in order to better understand the factors that confer morphogenetic stability on cells in the isolated islets.We demonstrated cytoplasmic immunoreactivity for TGF-beta isoforms over 8 days post isolation using canine islets. Islet-to-duct epithelial transdifferentiation was correlated with the total amount of TGF-beta and was maximal at 48 h of culture. Up regulation of TGF-betaRI and TGF-betaRII expression on day 2 post-isolation was demonstrated by immunohistochemistry and Western blot analysis, and correlated temporally with the induction of cell proliferation. The presence of TGF-beta1 in culture supernatants was detected using the PAI/L assay. The peak TGF-beta1 level was 10.94 +/- 2.27 pM (active form) and 52.23 +/- 1.57 pM (total TGF-beta) at 48h. Addition of exogenous TGF-beta1 at different concentrations caused an accelerated and more pronounced epithelial transformation at 5--10 ng/mL compared to lower concentrations (0.5--1 ng/mL).
These studies confirm the biological potential of islets of Langerhans to transdifferentiate to duct epithelial structures. TGF-beta signal transduction appears to play an important role in this process.
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Dech, Jeffery P. "Population establishment of Galerucella pusilla (Duft.) and G. calmariensis (L.) (Coleoptera, chrysomelidae) and their relative impact on the growth of Lythrum salicaria L. (Myrtiflorae: Lythraceae) in two central Ontario wetlands." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0009/MQ61258.pdf.
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Veizis, Ilir Elias. "Enhanced ERK1/2 activity a central feature of cystogenesis in ARPKD implications for ion transport phenotype /." Connect to text online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=case1102023062.
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Thesis (Ph. D.)--Case Western Reserve University, 2005.[School of Medicine] Department of Physiology and Biophysics. Includes bibliographical references. Available online via OhioLINK's ETD Center.
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Brauer, Frithjof [Verfasser]. "Dust particle growth in protoplanetary disks / presented by Frithjof Brauer." 2009. http://d-nb.info/993437168/34.
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Pei-ChiChen and 陳佩琪. "Water soluble chitosan inhibits nerve growth factor in murine model of house dust mite induced allergic rhinitis." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/93145337664130719056.
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碩士國立成功大學
微生物及免疫學研究所
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Allergic rhinitis (AR) is a disease with symptom of nasal airway hyperresponsiveness and mucosal inflammation mediated by IgE-associated processes. Nerve growth factor (NGF), a neurotrophin, has been shown to play an important role in neuroimmune responses by augmenting an existing type 2 T helper cell (TH2) immune response. Since chitin exhibits anti-inflammatory properties by inhibiting the development of allergic TH2 response, we aimed to assess the effect of the soluble derivatives of chitin—water soluble chitosan (WSC) on the NGF in a mouse model of Dermatophagoides pteronyssinus (Der p)-induced AR. First, we established an NGF-mediated AR toward augmenting systemic total and Der p-specific IgE levels, upper airway hyperresponsiveness, and local TH2 related immune response including the infiltration of eosinophils and degranulation of mast cells as well as TH2 related cytokines production in the nasal septum and nasal cavity lavage fluids. Interestingly, intranasal administration of WSC reduced allergic inflammation and improved the upper airway hyperresponsiveness. The expression of NGF and its related low affinity p75 neurotrophin receptors (p75NTR) as well as high affinity tyrosine kinase receptor A (TrkA) recptors in nasal epithelium of Der p-stimulated mice also repressed. Next, we used human nasal septum epithelial cell line (RPMI-2650) to investigate the detail mechanisms of candidate anti-allergic agents—WSC in attenuating Der p-induced airway inflammation. The results showed that NGF and TH2 related cytokines create an amplification loop resulting in broader allergic inflammation in upper-airway epithelial cells. In addition, WSC attenuated allergic inflammation and the epithelial cells damage through inhibiting NGF biosynthesis during allergic TH2 immune responses. In summary, we have demonstrated the role of NGF in a mouse model of house dust mite-induced AR, and the therapeutic effect of WSC in our AR mouse model, may through the attenuation NGF-induced airway inflammation as well as the inhibition of NGF synthesis. Our finding provides a new therapeutic modality of patients suffered with AR in clinical condition.
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Huang, Pei Han, and 黃珮涵. "Predicting Posttraumatic Growth Following Burn Injury: A Prospective Study of Survivors of 2015 Formosa Fun Coast Water Park Dust Explosion." Thesis, 2019. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107CGU05738010%22.&searchmode=basic.
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