Supersaturating Drug Delivery Systems (SDDS) could enhance oral bioavailability of poorly water soluble drugs (PWSD). Precipitation inhibitors (PIs) in SDDS could maintain supersaturation by inhibiting nucleation, crystal growth, or both. The mechanisms by which these effects are realized are generally unknown. The goal of this dissertation was to explore the mechanisms underpinning the effects of model PIs including hydroxypropyl β-cyclodextrins (HP-β-CD), hydroxypropyl methylcellulose (HPMC), and polyvinylpyrrolidone (PVP) on the crystal growth of indomethacin, a model PWSD. At high degrees of supersaturation (S), the crystal growth kinetics of indomethacin was bulk diffusion-controlled, which was attributed to a high energy form deposited on the seed crystals. At lower S, indomethacin growth kinetics was surface integration-controlled. The effect of HP-β-CD at high S was successfully modeled using the reactive diffusion layer theory. The superior effects of PVP and HPMC as compared to HP-β-CD at high S were attributed to a change in the rate limiting step from bulk diffusion to surface integration largely due to prevention of the high energy form formation. The effects of PIs at low S were attributed to significant retardation of the surface integration rate, a phenomenon that may reflect the adsorption of PIs onto the growing surface. PVP was selected to further understand the relationship between adsorption and crystal growth inhibition. The Langmuir adsorption isotherm model fit the adsorption isotherms of PVP and N-vinylpyrrolidone well. The affinity and extent of adsorption of PVP were significantly higher than those of N-vinylpyrrolidone, which was attributed to cooperative interactions between PVP and indomethacin. The extent of PVP adsorption on a weight-basis was greater for higher molecular weight PVP but less on a molar-basis indicating an increased percentage of loops and tails for higher molecular weight PVPs. PVP significantly inhibited indomethacin crystal growth at high S as compared to N-vinylpyrrolidone, which was attributed to a change in the growth mechanism resulting in a change in the rate limiting step from bulk diffusion to surface integration. Higher molecular weight PVPs were better inhibitors than lower molecular weight PVPs, which was attributed to a greater crystal growth barrier provided by a thicker adsorption layer.

No description available.

High quality semiconductor single crystals are the driving force behind today's rapidly growing electronic and communication industry. However, the growth of desired high quality crystals is difficult mainly due to the generation of defects and impurities in the grown crystal, and the segregation of species and strong convection in the liquid solution during growth. To minimize these undesirable effects, and to control segregation and convection, the use of magnetic fields (stationary, rotating, or traveling) has been widely considered. Static magnetic fields have been used to improve the quality of crystals by suppressing convection (Natural and/or Marangoni) and controlling the directional solidification and segregation of species. Rotating magnetic fields (RMF), on the other hand, have been used to obtain better mixing in the melt, better control for the heat and mass transport characteristics of the system and also for the shape of the growth interface. The objective of this thesis is to investigate the feasibility of using applied static vertical and rotating magnetic fields in Liquid Phase Diffusion (LPD) growth of SixGe1_x single crystals. To this end, a three-dimensional numerical simulation model was developed to study the heat, mass and momentum transfer characteristics of the Si-Ge solution under magnetic fields. The governing equations describing the fluid flow, heat and mass transport are solved numerically using the finite volume-based CFX software package of AEA Technology. In the simulation model, several complex user-defined subroutines have been developed to move the grid, to solve the scalar electric-charge balance equation for the electric potential distribution, and to include the magnetic body force terms. In addition, a command file is produced to define the physical properties of the solution and surrounding solids, and the numerical methods used, model topology, convergence criteria, and equation solvers. The results obtained from this study reveal that the use of a static vertical magnetic field is effective in suppressing natural convection. A magnetic field intensity of 0.3 Tesla is sufficient to provide significant suppression in the liquid Si-Ge solution. However, the static magnetic field does not provide the expected improvement on the growth interface shape. The use of RMF is, on the other hand, effective in creating a good mixing in the solution leading to more homogenous Si-Ge liquid. In addition, RMF is also very beneficial for creating a radially uniform solute distribution, thus flattening the growth interface for a stable growth.

Mathematical and numerical modelling of silicon germanium (SixGe1-x) crystal growth by liquid phase diffusion (LPD) was carried out in the Crystal Growth Laboratory at the University of Victoria. The crystal growth process was modelled using a relatively new. meshless. Lagrangian technique called smoothed particle hydrodynamics (SPH). The purpose of this modelling was to determine the suitability of the SPH method for simulating general crystal growth processes. Crystal growth simulations in the literature use a mesh-dependent Eulerian finite volume method, which requires complicated treatment of mesh adaptation at the crystal solidification surface. In contrast, the crystal solidification process can be modelled with relative ease using SPH. as this approach is automatically adaptable, and does not require a mesh. Several benchmark problems were also solved using SPH in order to investigate the problematic aspects of SPH simulation. It was found that. for simulations involving flows with low Reynolds numbers, SPH performed well even with relatively low particle number densities when compared with analytical and finite difference solutions. A simulation time study was also conducted for the two-dimensional driven cavity problem, in order to determine the simulation time as a function of particle resolution. This result showed that simulation times in the SPH method increase almost exponentially as the number of SPH particles is increased. The drastic increase in simulation times is due to the particle averaging procedure involving particle "neighbor. determination. in addition to the necessary reduction in time-step for a stable solution. The results of the LPD simulation using SPH were compared to the previously obtained solution found using the finite volume method. Although the thermal field computed by SPH agreed well with the finite volume results, the SPH velocity field broke down when domains having 738 and 2754 particles were used. The SPH concentration field was simulated correctly when the fluid flow was neglected. After an extensive, systematic review of the SPH coding. it was determined that the SPH method requires several thou-sands of particles to produce an accurate crystal growth simulation. where realistic Reynolds numbers are involved. Unfortunately. such a large number of particles requires unreasonable simulation times based on available computational power, and therefore SPH does not seem feasible for crystal growth simulations at this time. Future advances in computational power may render the SPH method comparable to the mesh-dependent approaches in terms of computational simulation times. At. that point in time. the SPIT approach would have significant advantages over mesh-dependent techniques when simulating crystal growth.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references. Also available via World Wide Web.

Thesis (Ph.D.)--McMaster University (Canada), 1992. / Source: Dissertation Abstracts International, Volume: 54-08, Section: B, page: 4182. Adviser: J. E. Greedan.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 107-110). Also available on the Internet.

Thesis (M.S.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Facilement excitable au moyen de diode InGaAs, l’ion Ytterbium trivalent présenteune émission infrarouge intéressante pour des applications laser. Les matériaux étudiés sontnombreux. Parmi eux, les borates sont des composés stables, transparents dans l’UV et présentant un seuil élevé au dommage. Ils sont par conséquent des bons candidats pour desapplications optiques. D’un point de vue structural, ils présentent une diversité de sitesd’accueil pour la terre rare ce qui permet de moduler les émissions obtenues en fonction de lacomposition.Nous avons mené une étude d’élaboration et de caractérisation sur un borate (à fusioncongruente) et deux oxyborates (à fusion non congruente) de composition : Li6Ln(BO3)3 ;LiGd6O5(BO3)3 ; Na3La9O3(BO3)8.Les différentes croissances cristallines, par la méthode Czochralski ou par la méthodedu flux, nous ont permis d’obtenir des cristaux de taille centimétrique comportant de largeszones transparentes, utiles pour les tests en cavité laser. L’étude spectroscopique de l’ionytterbium nous a permis d’évaluer l’éclatement des niveaux d’énergie et de localiser les ionsterres rares dans ces matrices. Différentes caractérisations thermiques, mécaniques et optiquesont aussi été réalisées sur les cristaux afin de pouvoir estimer les paramètres laser.Finalement, de premiers tests lasers ont été réalisés et ont montré la potentialité de cesmatériaux en tant que matériaux amplificateurs. / By the mean of InGaAs diode, trivalent ytterbium ions can give rise to an interestinginfrared emission for laser applications. Numerous compounds are in study. Among them,borates are stable, UV-transparent compounds and they have a high damage threshold. Thusthey are good candidates for optical applications. From a structural point of view, they exhibita diversity of host sites for the rare earth which allows to modulate emission withcomposition.We carry out an elaboration and characterization study on a borate and two oxyboratecompounds of formula Li6Ln(BO3)3 ; LiGd6O5(BO3)3 ; Na3La9O3(BO3)8.Crystal growth, by Czochralski or flux method depending on the meltingcharacteristic, enable us to obtain centimetric sized crystals with large transparent areas.Ytterbium ion spectroscopy study enables us to estimate energy levels splitting and to locaterare earth ions in these matrices. Several thermal, mechanical and optical characterizations were also performed on the crystals to estimate laser parameters. Finally, first laser tests werecarried out and have shown the potentiality of these materials as amplifier media.

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