Dissertations / Theses on the topic 'Particles'

Second phase particles play an important role in the recrystallization of aluminium alloys. They give rise to high level of local lattice misorientation around the particle, in particle deformation zone (PDZ) during processing. These can act as potent nucleation sites for new recrystallized grains in a process known as particle stimulated nucleation (PSN). This mechanism is essential to produce material with a more random texture and small grain size, which helps e.g. ductility and formability. A new HRDIC technique is used here in combination with EBSD to investigate the evolution of deformation structures by linking the local deformation (by Digital Image Correlation, DIC) to the lattice orientation before and after deformation by EBSD measurements and compared with the CPFEM predictions. The results show that strain is very heterogeneous during deformation and concentrates mainly in slip bands. The spacing between these bands is affected by several factors: applied strain, crystallographic orientation and the existence of small dispersoids. Thus, the relationship between the strain, particle size and rotation in the deformation zone is much more complex than predicted by existing models.

Laser flare can often be a major issue in particle image velocimetry (PIV) involving solid boundaries in a flow or a gas-liquid interface. The use of fluorescent light from dye-doped particles has been demonstrated in water applications, but reproducing the technique in an airflow is more difficult due to particle size constraints and safety concerns. The following thesis is formatted in a hybrid manuscript style, including a full paper presenting the applications of fluorescent Kiton Red 620 (KR620)-doped polystyrene latex microspheres in PIV. These particles used are small and monodisperse, with a mean diameter of 0.87 μm. The KR620 dye exhibits much lower toxicity than other common fluorescent dyes, and would be safe to use in large flow facilities. The first sections present a general introduction followed by a validation experiment using a standard PIV setup in a free jet. This work was the first to demonstrate PIV using fluorescent KR620-doped microspheres in an airflow, and results from the experiment were compared to similar data taken using standard PIV techniques. For the free jet results, Mie-scattered and fluorescent PIV were compared and showed average velocities within 3% of each other at the nozzle exit. Based on the PIV validation requirements used, this was deemed to be more of an indication of nozzle unsteadiness rather than an error or bias in the data. Furthermore, fluorescent PIV data obtained vector validation rates over 98%, well above the standard threshold of 95%. The journal article expands on the introductory work and analyzes testing scenarios where fluorescent PIV allows for velocity measurements much closer to a solid surface than standard, Mie-scattered PIV. The fluorescent signal from the particles is measured on average to be 320 ± 10 times weaker than the Mie scattering signal from the particles. This fluorescence-to-Mie ratio was found to be nonuniform, with the typical signal ratio for a single particle expected to fall between 120 and 870. This reduction in signal is counterbalanced by greatly enhanced contrast via optical rejection of the incident laser wavelength. Fluorescent PIV with these particles is shown to eliminate laser flare near surfaces, in one case leading to 63 times fewer spurious velocity vectors than an optimized Mie scattering implementation in a region more than 5 mm from an angled surface. In the appendix, a brief summary of an experiment to characterize the temperature sensitivity of the KR620 dye is included. This experiment concluded that the KR620 particles did not exhibit sufficient temperature sensitivity to warrant further investigation at the time.
Master of Science

Filtration is the most efficient method of aerosol monitoring and control. A number of theories (Bradley, 1932); (Hamaker, 1937); (Johnson et al., 1971); (Wang and Kasper, 1991); (Dahneke, 1995); (Wall et al., 1990) have been developed to describe the particle interaction with surface of a filter and to estimate the probability of the particle adhesion onto a surface. A range of the particle, filter and process parameters could contribute to the strength of the adhesion. Some of them are: hardness and cross-sectional shape of the fiber, smoothness of either the fiber or particle, air humidity, the effect of particle shape and many others. Obviously, the particle size (and correspondingly the surface area) also plays a crucial role in the bouncing processes. However, despite its importance in the research field the detailed mechanisms of the particle-fiber collision and possibility for the particle to bounce or to be re-entrained have not been fully explored. Therefore, there is a need for a theoretical and experimental knowledge concerning the influence of particle bouncing on filtration and separation processes. Although, some work on the effect of particle shape on filtration process has been done, there is still need for further research regarding the influence of motion of the particles of different shape along a fiber...
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Engineering
Science, Environment, Engineering and Technology
Full Text

Thesis: Ph. D. in Atmospheric Chemistry, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 197-219).
This thesis explores ways in which single particle mass spectrometry can be extended, whether through hardware improvements, or through the use of advanced data processing techniques to provide new kinds of aerosol chemistry measurements. Most of this work has been carried out using the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument, an aircraft deployable mass spectrometer that uses intense (~10 9 Wcm -2 ) UV laser pulses to vaporize and ionize single particles and measures their mass spectra using a time-of-flight mass spectrometer. Near-term and long-term hardware improvements as well as advanced data analysis techniques are explored in order to extract new chemical information from the thus obtained single particle mass spectra. Hardware improvements to PALMS are explored, such as the use of a high-powered femtosecond laser to obtain single particle mass spectra and a new high resolution compact mass analyzer. Also, a new commercial mass spectrometer LAAPToF is characterized and compared to PALMS. In addition to hardware improvements, novel data analysis techniques for analysis of single particle mass spectra were developed as a part of this work. In particular, a new method to identify biologically-derived particles is presented and used to derive vertical profiles of bioaerosol from near-surface to the upper troposphere.
by Maria Anna Zawadowicz.
Ph. D. in Atmospheric Chemistry

Thesis (M.S.)--University of Akron, Dept. of Mathematics, 2009.
"May, 2009." Title from electronic thesis title page (viewed 7/28/2009) Advisor, Dmitry Golovaty; Faculty Readers, Gerald Young, Patrick Wilber; Department Chair, Joseph Wilder; Dean of the College, Chand Midha; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Le but de cette étude expérimentale est de caractériser la dynamique de particules solides, à flottabilité nulle, incluse dans un écoulement turbulent isotrope en décroissance libre. Les particules utilisées sont de forme sphérique et ont un diamètre de 4 à 5 fois plus grand que l'échelle spatial de Kolmogorov de l'écoulement. De part leur taille, les particules ont également un nombre de Stokes proche de l'unité. On s'attend alors à ce que ces particules aient une dynamique différente de celle du fluide environnant. Dans cette étude, ont se propose de quantifier les différences de vitesses entre les deux phases à l'aide d'une technique de vélocimétrie simultanée
In this experimental study, the focus is made on the characterization of the dynamics of solid neutrally buoyant particles embedded in a freely decaying, nearly isotropic turbulence, with a weak mean flow. The particles are spherical with diameters several times larger than the Kolmogorov scale. The study of this flow configuration is still challenging both theoretically and numerically. Due to large particle sizes, the local flow around particles can not be considered as uniform and due to fluid-particle density ratio of around unity, the history and Basset forces cannot be neglected in comparison with the viscous drag force. Particle equation of motion is then fully non-linear, in contrast to the equation for heavy particles with diameters smaller then the Kolmogorov scale, for which only the Stokes drag is considered. In several experimental and numerical studies, the effect of particle size on velocity and acceleration statistics has been investigated (Homann and Bec 2010 ; Qureshi et al. 2008 ; Ouellette et al. 2008 ; Xu and Bodenschatz 2008). In the case of isotropic turbulence, Homann and Bec (2010) show that while the PDF of the particle velocity normalized by the square root of its variance does not vary with particle size, the variance itself is size dependent. A scaling relation for particle velocity variance has been proposed by using the Faxen correction (Gatignol 1983) which takes into account the non uniformity of the fluid flow at the scale of the particle. The aim of our research is to further study the dependence of particle dynamics on particle size. To that purpose, a turbulence generator has been set-up and the resulting turbulence is characterized. Then the flow was seeded with millimeter sized, neutrally-buoyant particles and the velocity of the two phases have been measured simultaneously. Simultaneous measurements of particle and surrounding fluid velocities show that although the global velocity statistics of the two phases have comparable values, the particles may have different local velocity from the velocity of the neighboring fluid

Afin de mesurer les durees de vie separees des hadrons beaux neutres et charges, les donnees enregistrees en 1991 et 1992 par le detecteur delphi du lep ont ete analysees. Les hadrons b sont identifies par leur desintegration en j psi, suivi de la desintegration de celui-ci en une paire de muons. Les performances du detecteur permettent de reconstruire avec precision les longueurs de vol des b dans le plan r phi, de meme que leur impulsion par une technique de regroupement de particules en jet, dont le j psi constitue le noyau. Le temps propre est ainsi determine evenement par evenement. L'estimation de la charge des hadrons b repose sur une methode de discrimination entre les particules qu'ils ont generees et celles provenant du processus de fragmentation. Apres selection, 80 evenements permettent de mesurer une duree de vie de 1,20 ps pour les hadrons b neutres et de 1,80 ps pour les b charges, avec une erreur de 0,40 ps dans les deux cas

This study aims to deduce an appropriate shape and density for an electronic free-cell that could be placed into a silo so that position and other desired physical parameters could be recorded. To determine how density and shape affects the trajectory and displacement of free cells, the trajectory and displacement of cylindrical, cuboid and triangular prism free-cells of equivalent volume was investigated in a discharging quasi 3D silo slice. The free-cells were placed at twelve different starting positions spread evenly over one half of the 3D slice. Tests were conducted using a monosized batch of spherical particles with a diameter of approximately 5 mm. Tests were also conducted in a binary mixture consisting of particles of different sizes (5 mm/4 mm) and the same density (1.28 g/cm3) and a binary mixture consisting of particles of different size (6 mm/5 mm) and different densities (1.16 g/cm3/1.28 g/cm3).The rotation of the free cells was also briefly discussed.Computer simulations were conducted using the Discrete Element Method (DEM). The simulation employed the spring-slider-dashpot contact model to represent the normal and tangential force components and the modified Euler integration scheme was applied to calculate the particle velocities and positions at each time step. One trial of each of the metal and plastic, cylindrical, cuboid and triangular prism free cells was compared with the average of three experimental trials. The trajectory and displacement of a representative particle positioned at the same starting position as the free cell was also obtained from DEM simulation and compared with the path and displacement of each of the free cells to determine which free cell followed the particle most closely and hence to determine a suitable free cell that would move with the rest of the grains. Spherical particles are idealised particles. Therefore tests were also conducted with a small number of polyhedral particles, to deduce their flow rate and the critical orifice width at which blockages were likely to form. Simulations were also conducted to test the feasibility of the DEM in modelling the behaviour of these polyhedral particles.Results indicate that for a free cell to move along the same trajectory and have the same displacement and velocity as an equivalent particle in the batch it should have a similar density to the majority of the other particles. A cylindrical free cell of similar density to the particles was found to follow the path of the representative particle more closely than the cuboid or triangular prism. Polyhedral particles were found to have a greater flow rate than spherical particles of equivalent volume.

Phase transitions and other intrinsic properties (shape, size, architecture) of molecularly structured aerosol particles are important for understanding their role in planetary atmospheres and for technical applications. By combining bath gas cooling with time resolved mid-infrared spectroscopy and modeling, information is obtained on dynamic processes and intrinsic properties of fluoroform and ethane aerosol particles. The distinct infrared spectral features of fluoroform aerosol particles make it a particularly suitable model system. Homogeneous crystallization rates of the sub-micron sized aerosol particles are determined (JV = 10⁸ - 10¹⁰ cm-³s-¹ or JS = 10³ – 10⁵ cm-²s-¹ at a temperature of T = 78 K), and the controversial question regarding volume versus surface nucleation in freezing aerosols is addressed. It is demonstrated that current state of the art measurements of droplet ensembles cannot distinguish between the two mechanisms due to inherent experimental uncertainties. The evolution of particle shape from spherical supercooled droplets to cube-like crystalline particles and eventually to elongated crystalline particles is recorded and analyzed in detail with the help of vibrational exciton model calculations. Phase behaviour of pure ethane aerosols and ethane aerosols formed in the presence of other ice nuclei under conditions mimicking Titan’s atmosphere provide evidence for the formation of supercooled liquid ethane aerosol droplets, which subsequently crystallize. The observed homogeneous freezing rates (JV = 10⁷ – 10⁹ cm-³s-¹) imply that supercooled ethane could play a similar role in ethane rich regions of Titan’s atmosphere as supercooled water does in the Earth’s atmosphere.

Colloidal particles and surfactants are commonly used, either individually or combined, as stabilisers of emulsions and foams. While the properties of surfactants and particles under a range of conditions and concentrations are relatively well known, there are some areas that require further investigation. The wettability of colloidal particles is one of the main factors that determine how they behave in a given system but determining the wettability is difficult due to the small size of the particles. The Film Calliper Method (FCM) has been proposed as a simple technique for the direct measurement of the contact angles of micrometer and submicrometer particles in their natural environment. One of the main aims of this work was to develop the Film Calliper Method for measuring contact angles at oil -water interfaces. The FCM was therefore used to measure the contact angles at oil - water interfaces for a range of particles, such as latex and silica particles, in different systems. For the first time directly measured contact angles are linked to the types of emulsions stabilised by the particles. The FCM was also used to directly measure the contact angles of silica particles in cationic surfactant solutions at air and oil interfaces for the first time. The stability of foams and emulsions made with particle - surfactant mixtures were investigated and related to the particle contact angles. Janus particles are a special category of particles which have different properties on each hemisphere. A method for making Janus particles was developed using template silica particles masked with a polymerised Pickering emulsion. The portion of surface exposed for treating can be tuned by controlling the inherent wettability of the template particles as proven with fluorescence microscopy. Emulsions stabilised by amphiphilic Janus particles made with the method are compared with emulsions stabilised by homogeneous particles with similar wettability.

Controlled release of an active is used in many applications. An example is drug delivery were it is desirable to release the active substance close to the target. In paints can anti-mold substances be encapsulated and released slowly during a long time which can extend the lifetime of the paint. This work investigated a coating process of loaded particles with as low leakage of the active substance as possible. It was also studied if the coating process was scalable. The particles in use were porous silica that was coated with sodium dodecyl sulphate (SDS), polyethyleneimine (PEI) and tetraethyl orthosilicate (TEOS). To fill particles, the active was dissolved in a solution and the particles were added. The active adsorbed into the pores of the particle. The coating principle was about the same for all layers. The coating molecules were dissolved in a solvent and the particles were added during stirring. After centrifugation the coated particles were separated from the solvent and left to dry. The thermogravimetric analyzer (TGA) was used to calculate the amount of adsorbed polymers on the particle surface. UV/VIS spectrometer analyzed the release rate of the active. As the recipe was optimized, SDS could be excluded from the process. An adsorption isotherm for PEI on the particle surface showed that 0.5 g PEI/ g particle the ratio required for covering the surface completely. It was proved that if the active was dissolved in all coating solutions during the coating, less leakage appear and makes the coating process more controlled. A higher amount of both PEI and TEOS improves the encapsulation of the active, which reduces the release rate. The coating process is proved to be scalable as the particle concentration is increased from 4.72 % to 16.5 % without too much agglomeration.

Diese Arbeit geht der Frage nach, ob MPn im Schwedischen syntaktisch Satzadverbien sind. Es wird gezeigt, dass sie sich syntaktisch von Satzadverbien unterscheiden und sich ferner in zwei getrennte Typen von MPn unterteilen lassen. Hierzu wird eine syntaktische Analyse vorgestellt, die diese Unterscheidung in dem phrasalen Status der MPn widerspiegelt. Die syntaktische Analyse wird durch sechs Experimente empirisch bestätigen. Ferner wird gezeigt, dass, um die Linearisierung von Elementen im Mittelfeld, am Beispiel von MPn, DPn und Objektpronomen im Mittelfeld, erklären zu können, nicht nur syntaktische Argumente herangeführt werden können, sondern auch phonologische Aspekte berücksichtigt werden müssen.
This thesis answers the question whether the MPs in Swedish are different from sentence adverbs on the level of syntax. It shows that MPs do differ from sentence adverbs, and further, that the MPs must be divided into two types. I present a syntactic analysis of the MPs that accounts for the two types of MPs as elements of distinct phrasal statuses. The syntactic analysis is tested empirically in six experiments and the results verified the analysis. Further I show that in order to account for the linearisation of MPs and object pronouns in the middle field, not only syntactic but also phonological properties of all elements must be taken into consideration.

La synthèse d’objets hybrides silice/latex constitue le coeur de ce travail de doctorat ; il s’agit de recouvrir partiellement des particules de polystyrène par de la silice nanométrique. Pour cela la polymérisation en émulsion de la phase organique in-situ en présence de nanoparticules de silice a été sélectionnée, en présence d’auxiliaires organiques pour rendre les surfaces amphiphiles. Les premières formulations mises en oeuvre avec des tensioactifs n’ont pas conduit à la décoration des latex parce que la présence de ces molécules aux interfaces favorise plutôt la dispersion des latex, empêchant l’adsorption de la silice. Par la suite, l’étude de deux systèmes composés respectivement d’une silice chargée négativement et du PEGMA, et d’une silice chargée positivement et du PSS, ont permis d’obtenir des latex « décorés » caractérisés par ATG et MET. Les mécanismes proposés s’appuient, selon les conditions, sur des mécanismes de nucléation homogène ou de nucléation en gouttelettes. Il apparait que la maîtrise des interactions pouvant être produites à la surface du latex est très importante pour permettre à la silice de se placer à sa surface. Ainsi, le choix de l’amorceur ou de l’auxiliaire organique est un paramètre clé pour obtenir des particules hybrides.Dans la dernière partie de cette étude, la silice a été introduite sous la forme d’objets hybrides silice/latex dans une suspension d’alumine pour procéder à l’hétérocoagulation des deux matériaux et à la granulation de l’alumine. La combinaison des propriétés des matériaux organique et inorganique constituant les particules hybrides a permis de conduire à l’amélioration de l’organisation microstructurale interne du granule lors de l’étape de séchage, en diminuant de manière significative les fissurations au sein des granules
This work is centered on the silica/latex hybrid particles synthesis: the aim of the study is to partially cover the polystyrene beads with silica nanoparticles. For this purpose, in-situ emulsion polymerization of the organic phase with silica has been selected with organic auxiliaries to make the surfaces amphiphilic. The first compositions processed with surfactants did not lead to latex decoration because the presence of the molecules at the interface favors the dispersion of the latex impeding silica adsorption. Then, the study of two systems with, in one hand negatively charged silica and PEGMA, and in the other hand positively charged silica and PSS, allowed to get “decorated” latex characterized by TGA and TEM. The proposed mechanisms are based on the homogeneous nucleation or the droplet nucleation mechanisms depending on the conditions. It appears that the control of the interactions that could be produced at the surface of the latex is very important to allow the silica to go at the surface. Thus, the initiator or organic auxiliary choice is a key parameter to get hybrid particles.In the last part of this study, silica has been introduced via hybrid particles in an alumina suspension to proceed to heterocoagulation of both materials leading to alumina granulation. The combination of the properties of the organic and inorganic material that constitute the hybrid particles leads to the improvement of the microstructural organization inside the spheres during the drying step by reducing significantly the cracks in the spheres

Background The foamy virus (FV) replication cycle displays several unique features, which set them apart from orthoretroviruses. First, like other B/D type orthoretroviruses, FV capsids preassemble at the centrosome, but more similar to hepadnaviruses, FV budding is strictly dependent on cognate viral glycoprotein coexpression. Second, the unusually broad host range of FV is thought to be due to use of a very common entry receptor present on host cell plasma membranes, because all cell lines tested in vitro so far are permissive. Results In order to take advantage of modern fluorescent microscopy techniques to study FV replication, we have created FV Gag proteins bearing a variety of protein tags and evaluated these for their ability to support various steps of FV replication. Addition of even small N-terminal HA-tags to FV Gag severely impaired FV particle release. For example, release was completely abrogated by an N-terminal autofluorescent protein (AFP) fusion, despite apparently normal intracellular capsid assembly. In contrast, C-terminal Gag-tags had only minor effects on particle assembly, egress and particle morphogenesis. The infectivity of C-terminal capsid-tagged FV vector particles was reduced up to 100-fold in comparison to wild type; however, infectivity was rescued by coexpression of wild type Gag and assembly of mixed particles. Specific dose-dependent binding of fluorescent FV particles to target cells was demonstrated in an Env-dependent manner, but not binding to target cell-extracted- or synthetic- lipids. Screening of target cells of various origins resulted in the identification of two cell lines, a human erythroid precursor- and a zebrafish- cell line, resistant to FV Env-mediated FV- and HIV-vector transduction. Conclusions We have established functional, autofluorescent foamy viral particles as a valuable new tool to study FV - host cell interactions using modern fluorescent imaging techniques. Furthermore, we succeeded for the first time in identifying two cell lines resistant to Prototype Foamy Virus Env-mediated gene transfer. Interestingly, both cell lines still displayed FV Env-dependent attachment of fluorescent retroviral particles, implying a post-binding block potentially due to lack of putative FV entry cofactors. These cell lines might ultimately lead to the identification of the currently unknown ubiquitous cellular entry receptor(s) of FVs.

The purpose of this study is to numerically investigate the turbulence modulation of polydisperse particles in a square particle-laden jet. Turbulence modulation describes the effects of fluctuating velocity and intensity when the particles and continuous fluid interact in a turbulent flow field. The rate at which turbulence modulation is altered is dependent upon parameters such as particle size, mass loading, Stokes number, coupling, volume fraction and mechanisms of turbulence modulation. This study modifies the analytical model developed by Yarin and Hetsroni (1993) to account for the transitional drag regime for coarse polydisperse particles. The particles under study are dilute, inert and spherical, with relatively high Stokes numbers, and classified as having two-way coupling with the fluid. The new analytical model is compared to numerical results using the Computational Fluid Dynamics (CFD) software FLUENT (ANSYS, Inc.). The turbulence model employed is the standard k-ε model. This study will analyze the effects of varying mass content and particle ratios to investigate how turbulence modulation is influenced. The new model and the CFD results show good agreement in the cases where the mass contents of each particle size are equal. This study will also look into the effects of polydispersion, and the concentration distribution, for indoor air applications. It was found that, in certain cases, the monodisperse assumption slightly over-predicts the concentration distribution in the enclosed region.
Master of Science

Background The foamy virus (FV) replication cycle displays several unique features, which set them apart from orthoretroviruses. First, like other B/D type orthoretroviruses, FV capsids preassemble at the centrosome, but more similar to hepadnaviruses, FV budding is strictly dependent on cognate viral glycoprotein coexpression. Second, the unusually broad host range of FV is thought to be due to use of a very common entry receptor present on host cell plasma membranes, because all cell lines tested in vitro so far are permissive. Results In order to take advantage of modern fluorescent microscopy techniques to study FV replication, we have created FV Gag proteins bearing a variety of protein tags and evaluated these for their ability to support various steps of FV replication. Addition of even small N-terminal HA-tags to FV Gag severely impaired FV particle release. For example, release was completely abrogated by an N-terminal autofluorescent protein (AFP) fusion, despite apparently normal intracellular capsid assembly. In contrast, C-terminal Gag-tags had only minor effects on particle assembly, egress and particle morphogenesis. The infectivity of C-terminal capsid-tagged FV vector particles was reduced up to 100-fold in comparison to wild type; however, infectivity was rescued by coexpression of wild type Gag and assembly of mixed particles. Specific dose-dependent binding of fluorescent FV particles to target cells was demonstrated in an Env-dependent manner, but not binding to target cell-extracted- or synthetic- lipids. Screening of target cells of various origins resulted in the identification of two cell lines, a human erythroid precursor- and a zebrafish- cell line, resistant to FV Env-mediated FV- and HIV-vector transduction. Conclusions We have established functional, autofluorescent foamy viral particles as a valuable new tool to study FV - host cell interactions using modern fluorescent imaging techniques. Furthermore, we succeeded for the first time in identifying two cell lines resistant to Prototype Foamy Virus Env-mediated gene transfer. Interestingly, both cell lines still displayed FV Env-dependent attachment of fluorescent retroviral particles, implying a post-binding block potentially due to lack of putative FV entry cofactors. These cell lines might ultimately lead to the identification of the currently unknown ubiquitous cellular entry receptor(s) of FVs.

Airborne particles play a major role in climate change and human health. Drawing on the results of extensive measurements carried out in the relatively clean environment of Brisbane and the heavily polluted megacity of Beijing, this thesis has significantly furthered our knowledge of the physical mechanisms of new particle formation in the lower atmosphere. Several characteristics of new particle formation events, such as their temporal distribution, the effect of wind speed and the role of atmospheric ions on the particle formation rate, were investigated for the very first time.

In this study the incipient motion of coarse solitary particles having different specific weights and shapes was investigated. A tilting flume of rectangular cross-section having a net working length of 12 m was used through the experiments. The slope of the channel and the discharge in the channel are the two basic variable parameters that determine the initiation of motion. Particles made of cement and mixture of cement and iron dust in certain ratios were used in the experiments with an obstructing element of various heights right behind the particles. Dimensionless hydraulic parameters determined from theoretical analysis were related to each other. Velocity profiles over the flow depths were measured and flow conditions corresponding to critical conditions were evaluated in terms of critical velocities and shear velocities. The findings of this study were compared with the results of similar studies given in the literature.

The understanding of human exposure to indoor particles of all sizes is important to enable exposure control and reduction, but especially for smaller particles since the smaller particles have a higher probability of penetration into the deeper parts of the respiratory tract and also contain higher levels of trace elements and toxins. Due to the limited understanding of the relationship between particle size and the health effects they cause, as well as instrument limitations, the available information on submicrometer (d < 1.0 µm) particles indoors, both in terms of mass and number concentrations, is still relatively limited. This PhD project was conducted as part of the South-East Queensland Air Quality program and Queensland Housing Study aimed at providing a better understanding of ambient particle concentrations within the indoor environment with a focus on exposure assessment and control. This PhD project was designed to investigate comprehensively the sources and sinks of indoor aerosol particles and the relationship between indoor and outdoor aerosol particles, particle and gaseous pollutant, as well as the association between indoor air pollutants and house characteristics by using, analysing and interpreting existing experimental data which were collected before this project commenced, as well as data from additional experiments which were designed and conducted for the purpose of this project. The focus of this research was on submicrometer particles with a diameter between 0.007 - 0.808 µm. The main outcome of this project may be summarised as following: * A comprehensive review of particle concentration levels and size distributions characteristics in the residential and non-industrial workplace environments was conducted. This review included only those studies in which more general trends were investigated, or could be concluded based on information provided in the papers. This review included four parts: 1) outdoor particles and their effect on indoor environments; 2) the relationship between indoor and outdoor concentration levels in the absence of indoor sources for naturally ventilated buildings; 3) indoor sources of particles: contribution to indoor concentration levels and the effect on I/O ratios for naturally ventilated buildings; and 4) indoor/outdoor relationship in mechanically ventilated buildings. * The relationship between indoor and outdoor airborne particles was investigated for sixteen residential houses in Brisbane, Australia, in the absence of operating indoor sources. Comparison of the ratios of indoor to outdoor particle concentrations revealed that while temporary values of the ratio vary in a broad range from 0.2 to 2.5 for both lower and higher ventilation conditions, average values of the ratios were very close to one regardless of ventilation conditions and of particle size range. The ratios were in the range from 0.78 to 1.07 for submicrometer particles, from 0.95 to 1.0 for supermicrometer particles and from 1.01 to 1.08 for PM2.5 fraction. Comparison of the time series of indoor to outdoor particle concentrations showed a clear positive relationship existing for many houses under normal ventilation conditions (estimated to be about and above 2 h-1), but not under minimum ventilation conditions (estimated to be about and below 1 h-1). These results suggest that for normal ventilation conditions and in the absence of operating indoor sources, outdoor particle concentrations could be used to predict instantaneous indoor particle concentrations but not for minium ventilation, unless air exchange rate is known, thus allowing for estimation of the "delay constant". * Diurnal variation of indoor submicrometer particle number and particle mass (approximation of PM2.5) concentrations was investigated in fifteen of the houses. The results show that there were clear diurnal variations in both particle number and approximation of PM2.5 concentrations, for all the investigated houses. The pattern of diurnal variations varied from house to house, however, there was always a close relationship between the concentration and human indoor activities. The average number and mass concentrations during indoor activities were (18.2±3.9)×10³ particles cm-³ and (15.5±7.9) µg m-³ respectively, and under non-activity conditions, (12.4±2.7)x10³ particles cm-³ (11.1±2.6) µg m-³, respectively. In general, there was a poor correlation between mass and number concentrations and the correlation coefficients were highly variable from day to day and from house to house. This implies that conclusions cannot be drawn about either one of the number or mass concentration characteristics of indoor particles, based on measurement of the other. The study also showed that it is unlikely that particle concentrations indoors could be represented by measurements conducted at a fixed monitoring station due to the large impact of indoor and local sources. * Emission characteristics of indoor particle sources in fourteen residential houses were quantified. In addition, characterizations of particles resulting from cooking conducted in an identical way in all the houses were measured. All the events of elevated particle concentrations were linked to indoor activities using house occupants diary entries, and catalogued into 21 different types of indoor activities. This enabled quantification of the effect of indoor sources on indoor particle concentrations as well as quantification of emission rates from the sources. For example, the study found that frying, grilling, stove use, toasting, cooking pizza, smoking, candle vaporizing eucalyptus oil and fan heater use, could elevate the indoor submicrometer particle number concentration levels by more than 5 times, while PM2.5 concentrations could be up to 3, 30 and 90 times higher than the background levels during smoking, frying and grilling, respectively. * Indoor particle deposition rates of size classified particles in the size range from 0.015 to 6 µm were quantified. Particle size distribution resulting from cooking, repeated under two different ventilation conditions in 14 houses, as well as changes to particle size distribution as a function of time, were measured using a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), and a DustTrak. Deposition rates were determined by regression fitting of the measured size-resolved particle number and PM2.5 concentration decay curves, and accounting for air exchange rate. The measured deposition rates were shown to be particle size dependent and they varied from house to house. The lowest deposition rates were found for particles in the size range from 0.2 to 0.3 µm for both minimum (air exchange rate: 0.61±0.45 h-1) and normal (air exchange rate: 3.00±1.23 h-1) ventilation conditions. The results of statistical analysis indicated that ventilation condition (measured in terms of air exchange rate) was an important factor affecting deposition rates for particles in the size range from 0.08 to 1.0 µm, but not for particles smaller than 0.08 µm or larger than 1.0 µm. Particle coagulation was assessed to be negligible compared to the two other processes of removal: ventilation and deposition. This study of particle deposition rates, the largest conducted so far in terms of the number of residential houses investigated, demonstrated trends in deposition rates comparable with studies previously reported, usually for significantly smaller samples of houses (often only one). However, the results compare better with studies which, similarly to this study, investigated cooking as a source of particles (particle sources investigated in other studies included general activity, cleaning, artificial particles, etc). * Residential indoor and outdoor 48 h average levels of nitrogen dioxide (NO2), 48h indoor submicrometer particle number concentration and the approximation of PM2.5 concentrations were measured simultaneously for fourteen houses. Statistical analyses of the correlation between indoor and outdoor pollutants (NO2 and particles) and the association between house characteristics and indoor pollutants were conducted. The average indoor and outdoor NO2 levels were 13.8 ± 6.3 ppb and 16.7 ± 4.2 ppb, respectively. The indoor/outdoor NO2 concentration ratio ranged from 0.4 to 2.3, with a median value of 0.82. Despite statistically significant correlations between outdoor and fixed site NO2 monitoring station concentrations (p = 0.014, p = 0.008), there was no significant correlation between either indoor and outdoor NO2 concentrations (p = 0.428), or between indoor and fixed site NO2 monitoring station concentrations (p = 0.252, p = 0.465,). However, there was a significant correlation between indoor NO2 concentration and indoor submicrometer aerosol particle number concentrations (p = 0.001), as well as between indoor PM2.5 and outdoor NO2 (p = 0.004). These results imply that the outdoor or fixed site monitoring concentration alone is a poor predictor of indoor NO2 concentration. * Analysis of variance indicated that there was no significant association between indoor PM2.5 and any of the house characteristics investigated (p > 0.05). However, associations between indoor submicrometer particle number concentration and some house characteristics (stove type, water heater type, number of cars and condition of paintwork) were significant at the 5% level. Associations between indoor NO2 and some house characteristics (house age, stove type, heating system, water heater type and floor type) were also significant (p < 0.05). The results of these analyses thus strongly suggest that the gas stove, gas heating system and gas water heater system are main indoor sources of indoor submicrometer particle and NO2 concentrations in the studied residential houses. The significant contributions of this PhD project to the knowledge of indoor particle included: 1) improving an understanding of indoor particles behaviour in residential houses, especially for submicrometer particle; 2) improving an understanding of indoor particle source and indoor particle sink characteristics, as well as their effects on indoor particle concentration levels in residential houses; 3) improving an understanding of the relationship between indoor and outdoor particles, the relationship between particle mass and particle number, correlation between indoor NO2 and indoor particles, as well as association between indoor particle, NO2 and house characteristics.

The understanding of human exposure to indoor particles of all sizes is important to enable exposure control and reduction, but especially for smaller particles since the smaller particles have a higher probability of penetration into the deeper parts of the respiratory tract and also contain higher levels of trace elements and toxins. Due to the limited understanding of the relationship between particle size and the health effects they cause, as well as instrument limitations, the available information on submicrometer (d < 1.0 µm) particles indoors, both in terms of mass and number concentrations, is still relatively limited. This PhD project was conducted as part of the South-East Queensland Air Quality program and Queensland Housing Study aimed at providing a better understanding of ambient particle concentrations within the indoor environment with a focus on exposure assessment and control. This PhD project was designed to investigate comprehensively the sources and sinks of indoor aerosol particles and the relationship between indoor and outdoor aerosol particles, particle and gaseous pollutant, as well as the association between indoor air pollutants and house characteristics by using, analysing and interpreting existing experimental data which were collected before this project commenced, as well as data from additional experiments which were designed and conducted for the purpose of this project. The focus of this research was on submicrometer particles with a diameter between 0.007 - 0.808 µm. The main outcome of this project may be summarised as following: * A comprehensive review of particle concentration levels and size distributions characteristics in the residential and non-industrial workplace environments was conducted. This review included only those studies in which more general trends were investigated, or could be concluded based on information provided in the papers. This review included four parts: 1) outdoor particles and their effect on indoor environments; 2) the relationship between indoor and outdoor concentration levels in the absence of indoor sources for naturally ventilated buildings; 3) indoor sources of particles: contribution to indoor concentration levels and the effect on I/O ratios for naturally ventilated buildings; and 4) indoor/outdoor relationship in mechanically ventilated buildings. * The relationship between indoor and outdoor airborne particles was investigated for sixteen residential houses in Brisbane, Australia, in the absence of operating indoor sources. Comparison of the ratios of indoor to outdoor particle concentrations revealed that while temporary values of the ratio vary in a broad range from 0.2 to 2.5 for both lower and higher ventilation conditions, average values of the ratios were very close to one regardless of ventilation conditions and of particle size range. The ratios were in the range from 0.78 to 1.07 for submicrometer particles, from 0.95 to 1.0 for supermicrometer particles and from 1.01 to 1.08 for PM2.5 fraction. Comparison of the time series of indoor to outdoor particle concentrations showed a clear positive relationship existing for many houses under normal ventilation conditions (estimated to be about and above 2 h-1), but not under minimum ventilation conditions (estimated to be about and below 1 h-1). These results suggest that for normal ventilation conditions and in the absence of operating indoor sources, outdoor particle concentrations could be used to predict instantaneous indoor particle concentrations but not for minium ventilation, unless air exchange rate is known, thus allowing for estimation of the "delay constant". * Diurnal variation of indoor submicrometer particle number and particle mass (approximation of PM2.5) concentrations was investigated in fifteen of the houses. The results show that there were clear diurnal variations in both particle number and approximation of PM2.5 concentrations, for all the investigated houses. The pattern of diurnal variations varied from house to house, however, there was always a close relationship between the concentration and human indoor activities. The average number and mass concentrations during indoor activities were (18.2±3.9)×10³ particles cm-³ and (15.5±7.9) µg m-³ respectively, and under non-activity conditions, (12.4±2.7)x10³ particles cm-³ (11.1±2.6) µg m-³, respectively. In general, there was a poor correlation between mass and number concentrations and the correlation coefficients were highly variable from day to day and from house to house. This implies that conclusions cannot be drawn about either one of the number or mass concentration characteristics of indoor particles, based on measurement of the other. The study also showed that it is unlikely that particle concentrations indoors could be represented by measurements conducted at a fixed monitoring station due to the large impact of indoor and local sources. * Emission characteristics of indoor particle sources in fourteen residential houses were quantified. In addition, characterizations of particles resulting from cooking conducted in an identical way in all the houses were measured. All the events of elevated particle concentrations were linked to indoor activities using house occupants diary entries, and catalogued into 21 different types of indoor activities. This enabled quantification of the effect of indoor sources on indoor particle concentrations as well as quantification of emission rates from the sources. For example, the study found that frying, grilling, stove use, toasting, cooking pizza, smoking, candle vaporizing eucalyptus oil and fan heater use, could elevate the indoor submicrometer particle number concentration levels by more than 5 times, while PM2.5 concentrations could be up to 3, 30 and 90 times higher than the background levels during smoking, frying and grilling, respectively. * Indoor particle deposition rates of size classified particles in the size range from 0.015 to 6 µm were quantified. Particle size distribution resulting from cooking, repeated under two different ventilation conditions in 14 houses, as well as changes to particle size distribution as a function of time, were measured using a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), and a DustTrak. Deposition rates were determined by regression fitting of the measured size-resolved particle number and PM2.5 concentration decay curves, and accounting for air exchange rate. The measured deposition rates were shown to be particle size dependent and they varied from house to house. The lowest deposition rates were found for particles in the size range from 0.2 to 0.3 µm for both minimum (air exchange rate: 0.61±0.45 h-1) and normal (air exchange rate: 3.00±1.23 h-1) ventilation conditions. The results of statistical analysis indicated that ventilation condition (measured in terms of air exchange rate) was an important factor affecting deposition rates for particles in the size range from 0.08 to 1.0 µm, but not for particles smaller than 0.08 µm or larger than 1.0 µm. Particle coagulation was assessed to be negligible compared to the two other processes of removal: ventilation and deposition. This study of particle deposition rates, the largest conducted so far in terms of the number of residential houses investigated, demonstrated trends in deposition rates comparable with studies previously reported, usually for significantly smaller samples of houses (often only one). However, the results compare better with studies which, similarly to this study, investigated cooking as a source of particles (particle sources investigated in other studies included general activity, cleaning, artificial particles, etc). * Residential indoor and outdoor 48 h average levels of nitrogen dioxide (NO2), 48h indoor submicrometer particle number concentration and the approximation of PM2.5 concentrations were measured simultaneously for fourteen houses. Statistical analyses of the correlation between indoor and outdoor pollutants (NO2 and particles) and the association between house characteristics and indoor pollutants were conducted. The average indoor and outdoor NO2 levels were 13.8 ± 6.3 ppb and 16.7 ± 4.2 ppb, respectively. The indoor/outdoor NO2 concentration ratio ranged from 0.4 to 2.3, with a median value of 0.82. Despite statistically significant correlations between outdoor and fixed site NO2 monitoring station concentrations (p = 0.014, p = 0.008), there was no significant correlation between either indoor and outdoor NO2 concentrations (p = 0.428), or between indoor and fixed site NO2 monitoring station concentrations (p = 0.252, p = 0.465,). However, there was a significant correlation between indoor NO2 concentration and indoor submicrometer aerosol particle number concentrations (p = 0.001), as well as between indoor PM2.5 and outdoor NO2 (p = 0.004). These results imply that the outdoor or fixed site monitoring concentration alone is a poor predictor of indoor NO2 concentration. * Analysis of variance indicated that there was no significant association between indoor PM2.5 and any of the house characteristics investigated (p > 0.05). However, associations between indoor submicrometer particle number concentration and some house characteristics (stove type, water heater type, number of cars and condition of paintwork) were significant at the 5% level. Associations between indoor NO2 and some house characteristics (house age, stove type, heating system, water heater type and floor type) were also significant (p < 0.05). The results of these analyses thus strongly suggest that the gas stove, gas heating system and gas water heater system are main indoor sources of indoor submicrometer particle and NO2 concentrations in the studied residential houses. The significant contributions of this PhD project to the knowledge of indoor particle included: 1) improving an understanding of indoor particles behaviour in residential houses, especially for submicrometer particle; 2) improving an understanding of indoor particle source and indoor particle sink characteristics, as well as their effects on indoor particle concentration levels in residential houses; 3) improving an understanding of the relationship between indoor and outdoor particles, the relationship between particle mass and particle number, correlation between indoor NO2 and indoor particles, as well as association between indoor particle, NO2 and house characteristics.

The area of particle characterization is expansive; it contains many technologies and methods of analysis. Light spectroscopy techniques yield information on the joint property distribution of particles, comprising the chemical composition, size, shape, and orientation of the particles. The objective of this dissertation is to develop a hybrid scattering-absorption model incorporating Mie and Rayleigh-Debye-Gans theory to characterize submicron particles in suspension with multiwavelength spectroscopy.Rayleigh-Debye-Gans theory (RDG) was chosen as a model to relate the particles joint property distribution to the light scattering and absorption phenomena for submicron particles. A correction model to instrument parameters of relevance was implemented to Rayleigh-Debye-Gans theory for spheres. Behavior of nonspherical particles using RDG theory was compared with Mie theory (as a reference). A multiwavelength assessment of Rayleigh-Debye-Gans theory for spheres was conducted where strict adherence to the limits could not be followed. Reported corrections to the refractive indices were implemented to RDG to try and achieve Mies spectral prediction for spheres.The results of studies conducted for RDG concluded the following. The angle of acceptance plays an important role in being able to assess and interpret spectral differences. Multiwavelength transmission spectra contains qualitative information on shape and orientation of non-spherical particles, and it should be possible to extract this information from carefully measured spectra. There is disagreement between Rayleigh-Debye-Gans and Mie theory for transmission simulations with spherical scatterers of different sizes and refractive indices.

Softening deformation of iron ore in the form of sinter, pellet, and lump ore in the cohesive zone of an ironmaking blast furnace is an important phenomenon that has a significant effect on gas permeability and consequently blast furnace production efficiency. The macroscopic softening deformation behavior of the bed and the microscopic deformation behavior of the individual particles in the packed bed are investigated in this study using wax balls to simulate the fused layer behavior of the cohesive zone. The effects of softening temperature, load pressure, and bed composition (mono - single melting particles, including pure or blend particles vs binary ??? two different melting point particles) on softening deformation are examined. The principal findings of this study are: 1. At low softening temperatures, an increase in load pressure increases the deformation rate almost linearly. 2. At higher softening temperatures, an increase in load pressure dramatically increases the deformation rate, and after a certain time there is no more significant change in deformation rate. 3. The bed deformation rate of a mono bed is much greater than that of a binary one. 4. In a binary system, the softening deformation rate increases almost proportionally with the increase in the amount of lower melting point wax balls. 5. In a mono system with blend particles, the content of the lower melting point material has a more significant effect on overall bed deformation than the higher melting point one. 6. The macro softening deformation of the bed behaves the theory of creep deformation. 7. A mathematical model for predicting bed porosity change due to softening deformation based on creep deformation theory has been developed. 8. Increase in load pressure also reduces the peak contact face number of the distribution curves, and this is more prominent with higher porosity values. 9. The contribution of contact face number to bed porosity reduction is more pronounced in a mono system than in a binary system. 10. The porosity reduction in a binary bed is more due to the contact face area increase, presumably of the lower melting point particles. 11. The mono system has a single peak contact face number distribution pattern while the binary system exhibits a bimodal distribution pattern once the higher melting point material starts to deform. 12. In a binary system, an increase in deformation condition severity tends to reduce the contact face number of the higher melting point material without having to increase the contact face number of the lower melting point material accordingly to achieve a given porosity.

Iron nanoparticles occur naturally in the environment, but their exposure increases dramatically due to the field of nanotechnology and –medicine. It is poorly understood how the intracellular cooperative mechanisms of submicron particles and microorganisms function on mammalian immune system. In this study, superparamagnetic iron oxide (SPIO) submicron particles will be used to benefit the research within environmental diseases, addressing the biocompatibility of these particles. The size-dependent effects in the immune system of two carboxyl coated SPIO particles with stated sizes 100 nm and 1 µm will be studied in vitro. It would be interesting to determine whether these particles were able to activate the inflammasome, but still, the precise molecular mechanisms for the activation remain unknown. In order to reveal the biocompatibility of these particles, tests were performed as a function of particle concentration ranging from 0.01 to 100 µg/mL using both whole blood and peripheral blood mononuclear cells (PBMC) isolated from healthy donors. The monocytes were first primed with Lipopolysaccharide from Escherichia coli 0111:B4 strain, followed by stimulation with increasing concentrations of the submicron particles. Flow cytometry on whole blood samples identified up-regulation of CD11b monocytes and granulocytes by the particles. In addition, Terminal Complement Complex analyses proved activation of the complement system. It is possible that the particles have been coated with C3b by the complement and phagocytized by the monocytes through CD11b/CD18 receptor. Cytokine secretion from monocytes and whole blood was measured with sandwich ELISA and Bio-plex. The smaller particles seemed to induce higher inflammatory responses than the larger ones. It was, however, interesting to find that the particles themselves caused secretion of active IL-1&#946; without being primed in advance. The mechanisms of the NLRP3 inflammasome activation might be explained by ROS production due to iron imbalance in the cytoplasm. Toxicity of the particles was seen at 10 µg/mL, suggesting their potentially low biocompatibility above this concentration. However, it is suggested better biocompatibility of the silica coated 1 µm particles than the polysaccharide coated 100 nm particles.

Computer simulation using the Discrete Element Method (DEM) has emerged as a powerful tool in studying the behaviour of particulate systems during powder flow and compaction. Contact law between particles is the most important input to the Discrete Element simulation. However, most of the present simulations employ over-simplistic contact laws which cannot capture the real behaviour of particulate systems. For example, plastic yielding, material brittleness, sophisticated particle geometry, surface roughness, and particle adhesion are all vitally important factors affecting the behaviour of particle interactions, but have been largely ignored in most of the DEM simulations. This is because it is very difficult to consider these factors in an analytical contact law which has been the characteristic approach in DEM simulations. This thesis presents a strategy for obtaining the contact laws numerically and a comprehensive study of all these factors using the numerical approach. A numerical method, named as the Material Point Method (MPM) in the literature, is selected and shown to be ideal to study the particle interactions. The method is further developed in this work in order to take into account all the factors listed above. For example, to study the brittle failure during particle impact, Weibull’s theory is incorporated into the material point method; to study the effect of particle adhesion, inter-atomic forces are borrowed from the Molecular Dynamic model and incorporated into the method. These developments themselves represent a major progress in the numerical technique, enabling the method to be applied to a much wider range of problems. The focus of the thesis is however on the contact laws between extremely fine particles. Using the numerical technique as a tool, the entire existing theoretical framework for particle contact is re-examined. It is shown that, whilst the analytical framework is difficult to capture the real particle behaviour, numerical contact laws should be used in its place.

This thesis describes experimental studies of colloidal particles dispersed in solvents which themselves have phase transitions. One common definition of soft matter is: a material characterized by a mesoscopic length scale. This length scale is, for example, the colloid size or the ordered domain size. Here we combine a complex host with one characteristic length scale with dispersed particles that have a different size. It might be anticipated that new behaviour will occur. Two limits of particle characteristics are probed: the case of dilute sterically-stabilized particles and the case of a weak gel of attractive particles. The two systems are polymer particles dispersed in a phaseseparating microemulsion and silica nanoparticles dispersed in a low molecular weight liquid crystal. In each system a temperature driven phase transition plays a crucial role. In the microemulsion case we observe how transitional and pre-transitional phenomena create effective interactions between particles and how new behaviour emerges in the host solvent in the late stage of the phase separation. We show that the pre-transitional clustering of the PMMA particles is due to an adsorbed layer of dodecane. Subsequently heterogeneous nucleation of the gas phase is seen. After phase separation has occurred in off-critical samples the particles remain in either the continuous or dispersed phase depending on the original microemulsion composition. In the late stage of the phaseseparation the coalescence and coarsening behaviour changes significantly, after more material exchange between the phases has taken place. This behaviour is reminiscent of viscoelastic phase separation in polymer based samples. In the liquid crystal case we discover the anisotropy of the liquid crystal persists over large length scales and modifies the local dynamics of the gel. Using electron microscopy and scattering techniques we demonstrate that the silica embedded in the liquid crystal forms agglomerates with a fractal structure. Rheological characterization demonstrates that the resulting composite is a gel. Investigation of the composite’s local dynamics using x-ray photon correlation spectroscopy shows anisotropy and intermittency in the dynamics on significant length scales. In both systems we have studied new behaviour seen due to the influence of one component on the dynamic characteristics of the other The pre- and post- phase transition phenomena are only crucial in the microemulsion case where the particles have purely repulsive interactions. Our results illustrate the subtle balances that occur in soft composite systems.

In part I we study quantum modified photon trajectories in a Schwarzschild blackhole spacetime. The photon vacuum polarization effect in curved spacetime leads to birefringence, i.e. the photon velocity becomes c±δc depending on its polarization. This velocity shift then results in modified photon trajectories. We find that photon trajectories are shifted by equal and opposite amounts for the two photon polarizations, as expected by the sum rule. Therefore, the critical circular orbit at u =1/3M in Schwarzschild spacetime, is split depending on polarization as u = 1/3M ± Aδ(M) (to first order in A), where A is a constant found to be ~ 10^-32 for a solar mass blackhole. Then using general quantum modified trajectory equations we find that photons projected into the blackhole for a critical impact parameter tend to the critical orbit associated with that polarization. We then use an impact parameter that is lower than the critical one. In this case the photons tend to the event horizon in coordinate time, and according to the affine parameter the photons fall into the singularity. This means even with the quantum corrections the event horizon behaves in the classic way, as expected from the horizon theorem. We also construct a quantum modified Schwarzschild metric, which encompasses the quantum polarization corrections. This is then used to derive the photons general quantum modified equations of motion, as before. We also show that when this modified metric is used with wave vectors for radically projected photons we obtain the classic equations of motion, as expected, because radial velocities are not modified by the quantum polarization correction. In Part II we use the 2+1d Nambu-Jona-Lasino (NJL) model to study the superfluid behaviour of two-dimensional quark matter. In previous work it was suggested that the high density phase of the 2+1d NJL model could be a relativistic gapless thin film BCS superfluid. In this work we find that as we raise the baryon chemical potential (µ) the baryon supercurrent jumps from a non-superfluid (zero) phase to a superfluid (non-zero) phase. This strongly first order transition is seen to occur at µ = 0.65, which was shown to be the point of chiral symmetry restoration. Therefore, we prove that at high density the 2+ 1d NJL model is in a superfluid phase. We then go on to study the dynamics of the superfluid phase, represented by the helicity modulus (Ү), which is the constant of proportionality between the supercurrent and the gradient of the diquark state function. We find that below the temperature associated with lattice size L_t = 4, the system is in a non-superfluid phase, and above L_t = 24 the system is in a superfluid phase. We also find a possible 2^nd order transition at L_t ≈ 6, which corresponds to the critical point as described by Kosterlitz and Thouless’ theory of 2D critical systems with U(1) global symmetry – such as the XY model.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 34-36).
An atomistic approach to modeling the sintering of nanocrystalline alloys has been developed. It has been shown that there exist alloys that exhibit both nanostructured stability and undergo an accelerated sintering process [1], [2]. However, the widespread adoption of such alloys has been limited by a lack of understanding of the processing kinetics that lead to the accelerated sintering phenomena. To better understand the role of surface diffusion, and the effect that system enthalpies of mixing have on inter-particle neck formation, a 3D kinetic monte carlo (KMC) model was proposed to study these phenomena. The results of these simulations demonstrate that positive enthalpy of mixing highlighted as a necessary criterion for nanocrystalline stability in [1], also leads to the fast diffusing elements ability to form the interparticle neck. The condition of lower temperature neck formation by fast diffusing alloy elements is hypothesized to be the mechanism behind which accelerated sintering occurs. The findings in this paper demonstrate that positive enthalpy of mixing alloys can be designed to sinter at lower temperatures and shorter cycle durations if they have adequate solute present on the surface of the particle.
by Jonathan Paras.
S.B.

We investigate random walk of a particle constrained on cells, where cells behave as a lattice gas on a two dimensional square lattice. By Monte Carlo simulation, we obtain the mean first passage time of the particle as a function of the density and temperature of the lattice gas. We find that the transportation of the particle becomes anomalously slow in a certain range of parameters because of the cross over in dynamics between the low and high density regimes; for low densities the dynamics of cells plays the essential role, and for high densities, the dynamics of the particle plays the dominant role.

Janus particles, named after the two faced Roman god Janus, possess unique asymmetry and combine two distinct functions at their opposite sides, allowing them to target complex self-assembled architectures and materials inaccessible for homogeneous building blocks. In this study, three areas regarding the topic of Janus particles were explored: the synthesis of Janus particles, their (self-) assembly, and applications. In the first part of the work, we have drawn our attention to the optimization of the synthetic procedures concerning the preparation of Janus particles and to the extending of the current Janus particle library by adding new geometries to the list. In the case of spherical Janus particles, we have developed an easy approach to tailor the Janus ratio of the resulting particles, thus, extending the possibilities of the Pickering emulsion approach for the creation of a variety of Janus particle architectures. Additionally, a new methodology was employed to measure directly and in situ the position/contact angle of the prepared Janus particles with different Janus ratios at a water-oil interface. It was further concluded that having simply two different functionalities on a particle surface does not necessarily imply amphiphilic behavior: only in the case of large wettability contrasts our particles were in a true Janus regime. In the case of platelet-like Janus particles, we have developed a completely new approach for their large-scale synthesis, which involved a reduced number of steps compared to the spherical Janus particles. In the second part of the work, the assembly behavior of various kinds of functional spherical Janus particles was investigated depending on the nature of the Janus particles and the surrounding media conditions. Oppositely charged, uncharged amphiphilic, and charged amphiphilic Janus particles were fabricated comprising different responsive polymers on their surface, and their assembly was investigated depending on the pH value of the dispersion, the ionic strength, or the solvent. It was found that, under specific conditions, the Janus particles formed hierarchical chain-like structures in solutions, which were not observed in the case of the homogeneous particle mixtures. The obtained results indicate that the fundamental understanding of the Janus particle assembly mechanisms is crucial for the programmed formation of desired structures. In the third part of the work, we have focused on the applications of our developed hybrid hairy Janus particles and proposed two main directions that would benefit from the unique properties or architecture of the Janus particles. The first direction is based on the exploitation of the superior interfacial activity of the Janus particles and their use for interfacial catalysis. The second proposed direction for the application of Janus particles is based on their use as building blocks for functional structured surfaces. The prepared surfaces were thoroughly characterized and tested for their performance toward anti-icing as well as anti-fouling applications. Ultimately, the developed functional surfaces based on Janus particles as building blocks are very promising for their future application in the coating technology.

We investigate random walk of a particle constrained on cells, where cells behave as a lattice gas on a two dimensional square lattice. By Monte Carlo simulation, we obtain the mean first passage time of the particle as a function of the density and temperature of the lattice gas. We find that the transportation of the particle becomes anomalously slow in a certain range of parameters because of the cross over in dynamics between the low and high density regimes; for low densities the dynamics of cells plays the essential role, and for high densities, the dynamics of the particle plays the dominant role.

This thesis reports theoretical and experimental work with the primary aim of developing new electrochemical methods to detect and characterise solid particles at the micron scale, specifically alumina (aluminium oxide) particles and graphene nanoplatelets, as representative of insulating and conductive particles, respectively. The fundamentals of thermodynamics, kinetics and mass transport in electrochemistry are introduced in Chapter 1, with the elaboration of electrodes, voltammetry and chronoamperometry used for electroanalysis. A comparison of non-electrochemical and electrochemical techniques used to analyse solid particles is also given. Chapter 2 provides information on both the experimental procedures and theoretical simulations used in the studies. Chapter 3 first investigates the oxidation of catechol (1,2-hydroxybenzene) in the pH range from 1.0 to 14.0 voltammetrically using a clean glassy carbon electrode. Analysis of the voltammograms allows the inference of the reaction mechanism in full and kinetics using a "scheme of squares". When the electrode surface is covered with sparse coverages of alumina particles, strong apparent catalysis of the reaction is discovered. The cause of such an apparent catalysis is then examined in Chapter 4. Comparison of the voltammograms at alumina- and graphene nanoplatelets-modified electrodes reveals that a change in the thermodynamics of the intermediate species, rather than a change of electron transfer rate, results in the apparent electrocatalysis of the redox process. With understanding of the oxidation of catechol electrocatalysed by alumina-modified electrodes, Chapter 5 reports to innovative "tagging" of catechol onto the surface of alumina. A new electrochemistry method based on particle impacts is used to quantify the adsorption of catechol on single alumina particles. In these experiments, particles suspended in solution impact a microelectrode held at a suitable potential for the oxidation or reduction of the adsorbed species. The current "spikes" induced from the impacts can be simulated to derive information such as the size of the particles, the surface coverage of modifiers, and the diffusion coefficients of charge transfer over the surface of the particles. The method is further applied to various modifiers, including 9,10-anthraquinone, tetrachloro-1,4-benzoquinone, and poly(vinylferrocene) in Chapter 6. The investigation of solid particles then proceeds from alumina to graphene nanoplatelets. In Chapter 7, graphene nanoplatelets are "tagged" with a ferrocene derivative prior to impact experiments. Two types of charge transfer are involved in the impacts: Faradaic due to redox of the modifier, and capacitative due to disruption of the electrical double layer at the electrode/solution interface. For the first time, both processes can be observed during the impacts of graphene nanoplatelets. Chapter 8 exploits the impacts method to evaluate the electron transfer rate of the ferrocene/ferrocenium redox couple immobilised on graphene nanoplatelets in aqueous solution. Single graphene nanoplatelets modified with poly(vinylferrocene) are allowed to impact a microelectrode. By adopting the potential applied, each graphene nanoplatelet temporarily acts as a "chemically modified nanoelectrode" for the duration of the impact, facilitating the resolution of fast electron transfer for the redox couple. Finally, Chapter 9 demonstrates the use of poly(vinylferrocene)-modified graphene nanoplatelets as a mediator for the oxidation of l-cysteine in aqueous solution. The theory of catalytic particle impacts is developed. The kinetics and mechanism of the catalysis is then assessed harnessing both experiment and theory.

The purpose of this study was to investigate whether or not differing base metals and filler wires used during welding processes contributed to differing amounts of ultrafine particles (UFP) and nanoparticles being emitted during the welding procedure. The study was also conducted to determine UFP and nanoparticle exposure in the breathing zones of the welders as well as the breathing zones of pipefitters and fire watchers, who commonly sit 6ft behind the welding arc. In order to determine if UFP and NP exposures differed with base metal and filler wire, all welding processes utilized the same welding machine for metal inert gas (MIG), the same wire speed, and the same voltages during each welding process. The only variation in welding procedures were cover gases used, base metals, and filler wires. Measurements gathered during welding procedures were conducted in the breathing zone of the welder and pipefitters consisted of UFP measurements taken by two different condensation particle counters (CPC), which operated in synchrony at the start and cessation of the welding process. NP measurements were taken by a NanoScan Scanning Mobility Particle Sizer (SMPS) and were also placed in the breathing zone of the welder. Lastly, particle characterization measurements for transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) were gathered using a filter attached to a high flow pump, which was placed in the breathing zone of the welder. According to the results, base metal and filler wire do emit differing amounts of NP and UFP during the welding processes. Carbon steel emits the highest amount of nanoparticles, while stainless steel emits the second highest amount, and inconel emits the least. The results also concluded that welders are exposed to a greater concentration of nanoparticles and UFPs than those experienced by pipefitters who stand 6ft from the welding arc.

Microfluidics research and development has emerged as a novel and promising tool for the development of sensors and actuators. However, one area in which microfluidics has been only minimally employed is in the handling of airborne particles, or aerosols. The real-time monitoring of aerosols is important for protecting human health and earth’s environment. The small size of microchannels, coupled with the opportunity to integrate sensing technologies, suggests them as a promising tool for the next generation of aerosol sensors. To that end, this thesis presents a microfluidics-based system for the size-separation of aerosols. Specifically, centrifugal force is exerted on each particle as it travels around a curved microchannel, resulting in the particle occupying a size-dependent lateral position in the channel. The behaviours of aerosols in a microchannel are examined, including the effects of flow focusing, the diffusion of airborne particles in a channel, and the centrifugal and viscous forces exerted on particles in a curved microchannel. Mathematical descriptions and computer simulations of these effects are developed to model these effects. Straight and curved microchannels were fabricated and each of these effects was measured experimentally, and compared to the models. Various combinations of airborne particles between 0.2 µm and 3.2 µm were successfully separated by size. A prototype optical particle detector was built and tested for its suitability as a candidate for integration with the microchannel particle separator. This represents the first approach in which aerosols have been separated by centrifugal forces in a microchannel, and one of very few approaches that have been used for any kind of size-based separation of airborne particles in microchannels. The small footprint and potential for integration offered by microsystem fabrication technology make it a desirable avenue of pursuit for the development of small, portable particulate monitors. The results presented here confirm that this approach to size-separation is a feasible option for a future microsystem based size-selective particulate monitor.

The regular transmittance of light or similar radiation through a flowing suspension of particles fluctuates because of the random occurrence of particles in the beam.In the work presented here, a theory for this fluctuating behaviour with the emphasison dispersions of mm-length slender cylindrical particles having circular crosssections is given. The particles in question are wood pulp fibres, which as a first approximation are considered to have a cylinder shape. Four possible measurementprinciples are described theoretically and experimentally. The four principles are for the measurement of concentration, length distribution characterized as lengthclasses, mean length, and mean width. The usefulness in industrial process monitoring of two of these principles is exemplified with pulp measurements. In order to estimate model errors, numerical simulations were used. Although other techniques such as image analysis may compete, the technique presented here is attractive because of the simplicity of the measurement device used.
QC 20100806