Clinopyroxene, olivine, plagioclase and hydrous fluid lithium partition coefficients have been measured between 800-1100oC at 1 GPa. Clinopyroxene-fluid partitioning is a function of temperature (ln DLicpx/fluid = -7.3 (+0.5) + 7.0 (+0.7) * 1000/T) and appears to increase with increasing pyroxene Al2O3 content. Olivine-fluid partitioning of lithium is a function of temperature (ln DLiol/fluid = -6.0 (+2.0) + 6.5 (+2.0) * 1000/T) and appears to be sensitive to olivine Mg/Fe content. Anorthite-fluid lithium partitioning is a function of feldspar composition, similar to the partitioning of other cations in the feldspar-fluid system. Isotopic fractionation between clinopyroxene and fluid, Licpx-fluid, has been measured between 900-1100oC and ranges from -0.3 to -3.4 ‰ (±1.4 ‰). Lithium diffusion has been measured in clinopyroxene at 800-1000oC and in olivine at 1000oC. The lithium diffusion coefficient is independent of the diffusion gradient as values are the same if the flux of lithium is into or out of the crystal and ranges from -15.19 ± 2.86 m2/s at 800oC to -11.97 ± 0.86 m2/s at 1000oC. Lithium diffusion in olivine was found to be two orders of magnitude slower than for clinopyroxene at similar conditions. Closure temperatures calculated for lithium diffusion in clinopyroxene range from ~400 to ~600oC. These results demonstrate that lithium equilibration between fluids and minerals is instantaneous, on a geological timescales. The confirmation of instantaneous equilibration, combined with min-fluid partition coefficients and values for Licpx-fluid, permits quantitative modeling of the evolution of lithium concentration and isotopic composition in slab-derived fluids during transport to the arc melt source. Our results indicate that fluids migrating by porous flow will rapidly exchange lithium with the mantle, effectively buffering the fluid composition close to ambient mantle values, and rapidly attenuating the slab lithium signature. Fluid transport mechanisms involving fracture flow are required to maintain a slab-like lithium signature (both elemental and isotopic) from the slab to the melt source of island arc basalts. This study demonstrates that mineral-fluid equilibration is rapid, and as a result the lithium content of minerals can only reliably represent chemical exchange in the very latest stages of the sample’s history.

Clinopyroxene, olivine, plagioclase and hydrous fluid lithium partition coefficients have been measured between 800-1100oC at 1 GPa. Clinopyroxene-fluid partitioning is a function of temperature (ln DLicpx/fluid = -7.3 (+0.5) + 7.0 (+0.7) * 1000/T) and appears to increase with increasing pyroxene Al2O3 content. Olivine-fluid partitioning of lithium is a function of temperature (ln DLiol/fluid = -6.0 (+2.0) + 6.5 (+2.0) * 1000/T) and appears to be sensitive to olivine Mg/Fe content. Anorthite-fluid lithium partitioning is a function of feldspar composition, similar to the partitioning of other cations in the feldspar-fluid system. Isotopic fractionation between clinopyroxene and fluid, Licpx-fluid, has been measured between 900-1100oC and ranges from -0.3 to -3.4 ‰ (±1.4 ‰). Lithium diffusion has been measured in clinopyroxene at 800-1000oC and in olivine at 1000oC. The lithium diffusion coefficient is independent of the diffusion gradient as values are the same if the flux of lithium is into or out of the crystal and ranges from -15.19 ± 2.86 m2/s at 800oC to -11.97 ± 0.86 m2/s at 1000oC. Lithium diffusion in olivine was found to be two orders of magnitude slower than for clinopyroxene at similar conditions. Closure temperatures calculated for lithium diffusion in clinopyroxene range from ~400 to ~600oC. These results demonstrate that lithium equilibration between fluids and minerals is instantaneous, on a geological timescales. The confirmation of instantaneous equilibration, combined with min-fluid partition coefficients and values for Licpx-fluid, permits quantitative modeling of the evolution of lithium concentration and isotopic composition in slab-derived fluids during transport to the arc melt source. Our results indicate that fluids migrating by porous flow will rapidly exchange lithium with the mantle, effectively buffering the fluid composition close to ambient mantle values, and rapidly attenuating the slab lithium signature. Fluid transport mechanisms involving fracture flow are required to maintain a slab-like lithium signature (both elemental and isotopic) from the slab to the melt source of island arc basalts. This study demonstrates that mineral-fluid equilibration is rapid, and as a result the lithium content of minerals can only reliably represent chemical exchange in the very latest stages of the sample’s history.

The main focus of this work is to investigate experimentally the transition to turbulence of a yield stress shear thinning fluid in Hagen-Poiseuille flow. By combining direct high speed imaging of the flow structures with Laser Doppler Velocimetry (LDV), we provide a systematic description of the different flow regimes from laminar to fully turbulent. Each flow regime is characterized by measurements of the radial velocity, velocity fluctuations, and turbulence intensity profiles. In addition we estimate the autocorrelation, the probability distribution, and the structure functions in an attempt to further characterize transition. For all cases tested, our results indicate that transition occurs only when the Reynolds stresses of the flow equals or exceeds the yield stress of the fluid, i.e. the plug is broken before transition commences. Once in transition and when turbulent, the behavior of the yield stress fluid is somewhat similar to a (simpler) shear thinning fluid. We have also observed the shape of slugs during transition and find that their leading edges to be highly elongated and located off the central axis of the pipe, for the non-Newtonian fluids examined. Finally we present a new phenomenological approach for quantifying laminar-turbulent transition in pipe flow. This criterion is based on averaging a local Reynolds number to give ReG. Our localised parameter shows strong radial variations that are maximal at approximately the radial positions where puffs first appear during the first stages of turbulent transition.

This PhD Thesis involves the development of a new synthetic protocol for iron oxide silica composite nanoparticles useful in MRI and magnetic hyperthermia. Our approximation combines the sol-gel chemistry and supercritical fluids to obtain biocompatible, spherical composite particles, with narrow particle size distribution. The composite particles showed very high values of relaxivity. We have also studied the dependence of the specific absorption rate with iron concentration. This manuscript is organized into seven chapters. Chapter 1 provides a general introduction to magnetic nanoparticles, their properties, synthesis, stabilization and applications, with special interest in the biomedical field. The aim of the chapter is to place the reader in the scientific context of the thesis. Chapter 2 describes the synthesis of nanoparticles by thermal decomposition of an iron complex, Fe(CO)5, and their characterization in solid and colloidal dispersion. Silica coating is a convenient approach to stabilize nanoparticles in a biocompatible way. In this thesis we have developed a new synthetic protocol to coat iron oxide nanoparticles with silica that combines the sol-gel chemistry and supercritical fluids. To understand and control the details of this procedure, we first synthesized nano- and microparticles of silica. They are described in Chapter 3. Chapter 4 includes the synthesis of the composite γ-Fe2O3@SiO2 nanoparticles. The core is composed of clustered iron oxide nanoparticles (described in Chapter 2) surrounded by a silica shell. Chapter 4 also describes the material characterization, with special emphasis on the magnetic properties, which will be exploited in the biomedical applications. We also succeeded in synthesizing composite ε-Fe2O3@SiO2 nanospheres from the previous γ-Fe2O3@SiO2 particles. The evaluation of the materials described in Chapters 2 and 4 as contrast agents for magnetic resonance imaging and as mediators for magnetic hyperthermia is included in Chapter 5. Chapter 6 lists the main conclusions derived from the present thesis. Finally, Chapter 7 gathers the annexes. It includes four publications arising from the main subject of this thesis, as well as five other publications and a patent on projects that I worked during the time that has lasted my doctoral thesis. The annexes also include a brief description of the experimental techniques used and protocols for sample preparation.

En aquest treball s'estudia la convecció en una capa plana de fluid entre dues superfícies perfectament conductores sotmesa a un gradient advers de temperatura. Es considera el problema bidimensional amb periodicitat en la direcció longitudinal i s'incideix especialment en la generació espontània de vents. Les condicions de contorn que s'utilitzen a les superfícies (cas rígid) permeten esforços tallants no nuls, per això s'ha permés l'existència, no només d'un flux amb vent, sinó d'un flux de massa net. El problema es planteja en una caixa periòdica de longitud L i s'analitzen solucions d'aquesta longitud tant amb una parella de rotlles com amb més d'una. Aquests dos casos requereixen un estudi diferent, és per això que el treball es divideix en dues parts. La primera part consta de:(1) l'anàlisi d'estabilitat de solucions amb una sola parella de rotlles, que, gràcies a les simetries del sistema, factoritza en quatre problemes. Es presenten les corbes d'estabilitat pel número de Prandtl 10, destacant que és per valors de L petits on, via una bifurcació de Hopf, es genera vent amb un perfil antisimètric i que es troba una corba que presenta una bifurcació subcrítica estacionària amb vent antisimètric degut a la ressonància d'estats purs 1:2,(2) la dinàmica dels rotlles per a número de Prandtl 10, fixant alguns valors de L que són significatius de la dinàmica per aquest valor del número de Prandtl. En tots els casos, augmentant el número de Rayleigh, apareixen vents que bifurquen o no del flux bàsic i com a etapa final sempre es generen solucions amb un flux de massa net, solucions que han perdut qualsevol simetria, (3) un model d'equacions d'amplitud que justifica el caràcter de les bifurcacions secundàries i permet entendre el comportament no lineal de les solucions prop de la bifurcació. La segona part consta de:(4) l'anàlisi d'estabilitat de totes les solucions amb més d'una parella de rotlles enfront de qualsevol pertorbació periòdica que pugui cabre al contenidor. Utilitzant la teoria de Floquet es pot reduïr l'anàlisi a un domini de longitud la periodicitat bàsica de la solució. Això permet calcular quin és el rang de paràmetres on les parelles de rotlles són estables enfront de qualsevol pertorbació periòdica (es presenta el cas amb número de Prandtl 10). Els resultats ens diuen que les ressonàncies n-1:n amb n>1 dominen 'estabilitat de n parelles de rotlles,(5) el càlcul de totes les solucions estacionàries amb les mateixes simetries que els rotlles primaris. S'observa que ,el fet de que, fixant paràmetres, no hi hagi unicitat de solucions es deu a les ressonàncies 1:2n+1. / Thermal convection in a planar fluid layer with perfectly conducting surfaces and with an advers temperature gradient is studied. The bidimensional problem with periodicity in the longitudinal is considered. The spontaneous generation of winds is the main goal of this work. Rigid boundary conditions are used in the vertical, allowing the generation of a mean flow and a net mean mass flux. We set out the problem in a periodic container with lenght L and we analize solutions with this lenght containing one o more pairs of rolls. This two cases need a different study, is for this reasonthe work is divided into two parts. The firs part contains:(1) the stability analysis of solutions with one pair of rolls. This analysis , due to the symmetries of the system, factorize into four problems. The stability curves with Prandtl number 10 are calculated. We observe that for small values of $L$ a mean flow with an antisymmetric mean flow is generated via a Hopf bifurcation. We also detect a curve that presents a subcritical steady state bifurcation with an antisymmetric mean flow. This curve is due to the 1:2 resonance of pure mode states, (2) the nonlinear dynamics of rolls with Prandtl number 10 for some values of L, significant of the dynamics of this Prandtl number. In all cases, increasing the Rayleigh number, an spontaneos mean flow is generated. These mean flow can or cannot bifurcate from the basic convective regime but the final solutions present a net mean mass flux and no symmetries are present, (3) a model of amplitude equations that interprets the caracter of secundary bifurcations and nonlinear dynamics of them near the bifurcation. The second part contains:(4) the stability analysis of solutions with more than one pair of rolls with respect periodic perturbations. Using Floquet theory we reduce the analysis to a container with lenght the basic periodicity of solution. With this simplication we calculate the rang of parameters with stable pairs of rolls with respect any periodic instability (the case Prandtl number 10 is presented). The resultsclarify that the n-1:n resonances with n>1 dominate the stability of n pairs of rolls.(5) the research of all steady solutions with same symmetries that primary rolls. We observe that 1:2n+1 resonances produce the non-unicity of these solutions when some parameter values are fixed.

Tornado simulations in the visual effects industry have always been an interesting problem. Developing tools to provide more control over such effects is an important and challenging task. Current methods to achieve these effects use either particle systems or fluid simulation. Particle systems give a lot of control over the simulation but do not take into account the fluid characteristics of tornadoes. The other method which involves fluid simulation models the fluid behavior accurately but does not give control over the simulation. In this thesis, a novel method to model tornado behavior is presented. A tool based on this method was also created. The method proposed in this thesis uses a hybrid approach that combines the flexibility of particle systems while producing interesting swirling motions inherent in the fluids. The main focus of the research is on providing easy-to-use controls for art directors to help them achieve the desired look of the simulation effectively. A variety of controls is provided which include the overall shape, path, rotation, debris, surface, swirling motion, and interaction with the environment. The implementation was done in Houdini, which is a 3D animation software whose node based system allows an algorithmic approach to the problem and integrates well with the current tools. The tool allows the user to create animations that reflect the visual characteristics of real tornadoes. The usefulness of the tool was evaluated among participants who had some experience in 3D animation software. The results from the simulation and evaluation feedback reveal that the tool successfully allowed the users to create tornadoes of their choice efficiently.

Abstract In this paper, the optical properties of magnetic fluid thin films are studied. We present the experimental observation of optical linear birefringence and dichroism in magnetic fluid thin film induced by crossed magnetic field perpendicular to the direction of light propagation. According to our results, we ascertain that both the magnetic birefringence and dichroism are existed. Besides, we also find that the relations between magnetic field and magneto-optical effects changed with the applied magnetic field intensity.

Four in vitro models were used to measure the antioxidant activity of 11 citrus phytochemicals. The citrus limonoids and bergapten showed very weak antioxidant activity. The flavonoids demonstrated mild, to moderate, to strong antioxidant activity. In addition to some other commonly accepted structural features our data indicated that the hydroxyl group in position 6 of ring A could also increase the antioxidant activity of flavonoids. Compared with the active flavonoids, limonoids are highly oxygenated triterpenoids, with fewer hydroxyl groups to stabilize unpaired electrons (or scavenge free radicals). Bergapten lacks a hydroxyl group. This is the first report on the antioxidant activity of limonoids and neoeriocitrin. A feeding study using Syrian hamsters was followed to determine the effect of citrus limonoids and flavonoids on plasma cholesterol. Hamsters fed with limonin, limonin 17-Beta-D-glucopyranoside and grapefruit pulp significantly inhibited the increase of LDL/HDL-cholesterol (36.6%, 52.9% and 57% respectively) compared with the basal control (65.8%) and the pectin control (70%). Furthermore, hamsters fed with limonin had significantly larger LDL particle size (21.21 nm) compared with the control group (19.96 nm). Further studies demonstrated that LDLs from hamsters fed with limonin and limonin 17-Beta-D-glucopyranoside were less susceptible to oxidation. These data suggest that limonin, limonin 17-Beta-D-glucopyranoside and grapefruit pulp have potential inhibitory effects against atherogenesis. Supercritical CO2 (SC-CO2) was attempted to extract limonoids from grapefruit seeds and molasses. Limonin aglycone was successfully extracted with SC-CO2 directly from grapefruit seeds with the yield of 6.3 mg/g seeds at 48.3 MPa, 50˚C and 60 min with CO2 top feeding; and the limonin glucoside was extracted using SC-CO2 and ethanol as co-solvent from the defatted seeds with the yield of 0.73 mg/g seeds at 42 MPa, 52˚C, 45% ethanol (XEth=0.45) and 40 min with CO2 top feeding; and limonin glucoside also was extracted using SC-CO2 and ethanol with the yield of 0.61mg/g grapefruit molasses at 48.3 MPa, 50˚C and 10% ethanol (XEth=0.1), 40 min with CO2 top feeding. CO2 flow rate was around~5 l/min in experiments. The results demonstrated SC-CO2 extraction of limonoids from citrus juice industry byproducts has practical significance for future commercial production.

Thesis (Ph.D.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves [143]-150.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 136-143). Also available on the Internet.