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Source: Dissertation Abstracts International, Volume: 35-07, Section: B, page: 3462. / Thesis (Ph.D.)--The Florida State University, 1974.

An experimental study of the steady-state and dynamic characteristics of gas-liquid mixing in an agitated vessel has been made. The effect of impeller speed and gassing rate on the power consumption, bubble size, gas holdup and specific interfacial area was investigated over a wide range of conditions, in both coalescing and 'non-coalescing' systems. A further extension of this included the effect of continuous liquid flow. The experiments were carried out using a fully baffled tank of 0.2m diameter and three sizes of Rushton turbine with D/T = 0.375 to 0.66. The bubble size in the vessel was measured by a capillary probe technique. In the ungassed state (no sparging of gas) and at sufficiently high Reynolds number, surface aeration plays an important role. Sampling of the entrained bubbles near to the liquid surface and in the impelle region revealed that surface aeration takes place before there is any drop in Power number and at correspondingly much lower impeller speeds A mechanism for surface aeration is proposed and correlations are presented. A new measure of gas dispersion efficiency has been defined. It can be used to identify the different regions of gas-liquid mixing as well as providing estimates of the degree of flooding or gas recirculation. The correlations of gas dispersion obtained from the gassed power measurements enable a more accurate prediction of Pg to be made for any region of gas-liquid mixing. The impeller power response has been studied using pulse and step change in gas flow rate. These dynamical measurements have provided further insight into the cavity formation processes occurring behind the impeller blades and the reverse process of cavity stripping. A simple lumped parameter model has been proposed to describe the process of cavity formation. The physical implications of this model are analysed and estimates of obtained are compared with the steady-state results. Extensive measurements have been made of the bubble size produced in air-water and air-electrolyte dispersions. These are presented in the form of spatial and point distributions, gas-holdup and specific interfacial area. Averaged overall estiamtes of these dispersion properties have been analysed and compared with other results and correlations. The position of the inlet and outlet liquid flows in a continuous-flow system have a very significant effect on the gas-liquid mixing. However, having the liquid inlet at the bottom of the tank and the outlet pipe at the side does not substantially alter the pattern of mixing from that observed in a batch vessel.

This dissertation offers a hopeful advance towards our future in space. Materials for space applications need to be strong, lightweight, and be multifunctional. Single-walled carbon nanotubes (SWNTs) have various properties that fit these criteria as a novel material for space and biomedical applications. To utilize SWNTs for this purpose, new chemical functionalization schemes need to be developed and studied. Fluorinated single-walled carbon nanotubes (F-SWNTs) with fluorine atom substitutions on the sidewalls can serve as the building blocks for the new functionalization schemes. In this work, F-SWNTs have been derivatized with urea, guanidine, thiourea, and alkylated chains that have also been perfluorinated. In addition to these materials, F-SWNTs have been modified with amino acids and silanes of various lengths. Finally, the F-SWNTs, Urea-F-SWNTs, and alkylated and perfluorinated SWNTs have been further employed in new composite materials and in radiation damage studies of the types that might be encountered in space. The Urea-F-SWNTs have also been derivatized with nanodiamonds (NT-ND) and coated onto glass as a potential new coating for space applications. The polymers in the composite studies were medium density polyethylene (MDPE) and high density polyethylene (HDPE) and nylon fibers. The MDPE polymer nanocomposites with the perfluorinated nanotubes showed an increase of 51% in tensile strength. The nylon fiber study showed the effect of a reactive vs. non-reactive nano filer with SWNTs and F-SWNTs, on mechanical and thermal properties and alignment through Raman spectroscopy studies. Among these functionalized materials, F-SWNTs, Urea-F-SWNTs, alkylated (F-SWNT-C11H23), and perfluorinated (F-SWNT-C11 FxHy) nanotubes in both powder and as fillers in thermoplastic composites were subjected to radiation damage studies. The radiation damage studies involved various ionizing radiation particles and photons, such as protons of different energies and fluences, gamma rays, neutrons and other ions, and focused on the damage done to the functionalized materials. Protons with an energy of 30 MeV and fluences ranging from 1x109 to 5x1010 protons/cm2 had a de-functionalizing effect on F-SWNT as evidenced by the increased G:D ratio in the Raman spectra from 0.76 for an unradiated sample compared to 1.98 for an irradiated one. XPS studies also indicated a decrease of fluorine atom substitution from 40.3 to 36.5%fluorine. Sensor studies, however, showed a slight decrease in the G:D ratio which indicated that the fluorinated nanotubes were further disordered on the sidewall due to proton irradiation damage. F-SWNT-C 11H23 and F-SWNT-C11FxHy were also placed on a sensor chip, with both types of materials showing sensitivity in terms of increased resistance to 10 and 30 MeV protons with fluences of 1x1011 and lx107protons/cm2 respectively. Both had shown recovery to baseline resistance when the radiation was discontinued. Non-functionalized SWNTs had shown no significant change in resistance after irradiation. In general, this sensor work showed that functionalized SWNTs serve as better radiation detector platform then their pristine counterparts. The HDPE nanocomposite studies showed that various radiation environments increased or decreased the melting temperature compared to a control. The effects of protons on unfunctionalized SWNTs were also studied to gauge whether SWNTs could serve as a potential radiation shielding material against neutrons, and it was determined that composites with SWNTs performed as well as other material candidates such as carbon black and neat HDPE, and functional nanomaterials could be considered for further experiments. Overall, this work has produced a variety of new SWNT derivatives for biomedical, sensor and structural applications. The new alkylated and perfluorinated nanotube materials increased the tensile strength of polyethylene and could be used as a potential reinforcing structural material. Finally, the radiation studies of this work showed that various particles and photons have a measurable effect on the stability of SWNT covalently-bonded sidewall substituents and on the internal diameter of the SWNTs themselves. This pattern of radiation damage to the various SWNT materials suggest potential applications of these materials for advanced sensor and shielding devices for space exploration.

The electrostatic properties of lipid bilayer membranes play a significant role in many biological processes. Atomic force microscopy (AFM) is highly sensitive to membrane surface potential in electrolyte solutions. With fully characterized probe tips, AFM can perform quantitative electrostatic analysis of lipid membranes. Electrostatic interactions between Silicon nitride probes and supported zwitterionic dioleoylphosphatidylcholine (DOPC) bilayer with a variable fraction of anionic dioleoylphosphatidylserine (DOPS) were measured by AFM. Classical Gouy-Chapman theory was used to model the membrane electrostatics. The nonlinear Poisson-Boltzmann equation was numerically solved with finite element method to provide the potential distribution around the AFM tips. Theoretical tip-sample electrostatic interactions were calculated with the surface integral of both Maxwell and osmotic stress tensors on tip surface. The measured forces were interpreted with theoretical forces and the resulting surface charge densities of the membrane surfaces were in quantitative agreement with the Gouy-Chapman-Stern model of membrane charge regulation. It was demonstrated that the AFM can quantitatively detect membrane surface potential at a separation of several screening lengths, and that the AFM probe only perturbs the membrane surface potential by <2%. One important application of this technique is to estimate the dipole density of lipid membrane. Electrostatic analysis of DOPC lipid bilayers with the AFM reveals a repulsive force between the negatively charged probe tips and the zwitterionic lipid bilayers. This unexpected interaction has been analyzed quantitatively to reveal that the repulsion is due to a weak external field created by the internai membrane dipole moment. The analysis yields a dipole moment of 1.5 Debye per lipid with a dipole potential of +275 mV for supported DOPC membranes. This new ability to quantitatively measure the membrane dipole density in a noninvasive manner will be useful in identifying the biological effects of the dipole potential. Finally, heterogeneous model membranes were studied with fluid electric force microscopy (FEFM). Electrostatic mapping was demonstrated with 50 nm resolution. The capabilities of quantitative electrostatic measurement and lateral charge density mapping make AFM a unique and powerful probe of membrane electrostatics.

The local surface plasmon resonance (LSPR) of noble metal nanoparticles has recently been exploited in numerous applications. The LSPR peak position and linewidth have been studied quite extensively, but the magnitude of the resonance has not received much attention. Analytical solutions to Maxwell's Equations cannot predict the scattering cross section of arbitrarily-shaped particles at arbitrary illumination and detection angles. Dark field microscpectroscopy is a powerful tool for studying plasmon resonances of noble metal nanoparticles and for developing their applications in sensing and imaging. We present a technique for calibrating dark field microspectrometer measurements to yield quantitative spectral scattering cross sections for arbitrarily shaped particles. Values for gold nanorods and gold bipyramids are reported. The measurements suggest that, for small elongated particles, the signal can be predicted by approximations based on the total cross section.

The experimental success in ultra-cold atomic gases, both bosonic and fermionic have boosted the theoretical studies, and especially the a lot of numerical techniques have been developed and used to describe them. In this thesis, we introduce two numerical experiments in our group on ultra-cold atomic gases. The first concerns the scalar dipolar condensate. We have developed and implemented a Split-Step Fourier scheme in imaginary time, which enable us to seek the ground state of the dipolar condensate. The second part is focused on our ongoing efforts to investigate the trapped spin polarized Fermi gas using self-consistent Bogoliubov-de Gennes (BdG) calculation.

This thesis presents a new 3-D shear velocity (Vs) model of the lithospheric structure beneath the Colorado Plateau and its surrounding regions to understand the complicated lithospheric modifications caused by major Cenozoic tectonic and magmatic activities. Prior to this work, lack of an overall velocity model had prevented a comprehensive understanding of the current encroachment patterns near the margins, and of the perplexing crust/mantle boundary beneath the plateau. Using the new USArray data, I have inverted the isotropic Vs model from the Rayleigh wave dispersion curves obtained by a modified two-plane wave method. The resulting Vs structures not only clearly image the sublithospheric low-velocity channels, but also identify the high velocity anomalies underlying the western plateau for the first time in surface wave tomography to support the recent delamination hypothesis. This work also provides a high-resolution velocity model for geodynamic modeling on lithosphere-asthenosphere interactions.

<p>Student learning in upper-division physics courses is a growing area of research in the field of Physics Education. Developing effective new curricular materials and pedagogical techniques to improve student learning in upper-division courses requires knowledge of both what material students struggle with and what curricular approaches help to overcome these struggles. To facilitate the course transformation process for one specific content area -- upper-division electrostatics -- this thesis presents two new methodological tools: (1) an analytical framework designed to investigate students' struggles with the advanced physics content and mathematically sophisticated tools/techniques required at the junior and senior level, and (2) a new multiple-response conceptual assessment designed to measure student learning and assess the effectiveness of different curricular approaches. We first describe the development and theoretical grounding of a new analytical framework designed to characterize how students use mathematical tools and techniques during physics problem solving. We apply this framework to investigate student difficulties with three specific mathematical tools used in upper-division electrostatics: multivariable integration in the context of Coulomb's law, the Dirac delta function in the context of expressing volume charge densities, and separation of variables as a technique to solve Laplace's equation. We find a number of common themes in students' difficulties around these mathematical tools including: recognizing when a particular mathematical tool is appropriate for a given physics problem, mapping between the specific physical context and the formal mathematical structures, and reflecting spontaneously on the solution to a physics problem to gain physical insight or ensure consistency with expected results. We then describe the development of a novel, multiple-response version of an existing conceptual assessment in upper-division electrostatics courses. The goal of this new version is to provide an easily-graded electrostatics assessment that can potentially be implemented to investigate student learning on a large scale. We show that student performance on the new multiple-response version exhibits a significant degree of consistency with performance on the free-response version, and that it continues to provide significant insight into student reasoning and student difficulties. Moreover, we demonstrate that the new assessment is both valid and reliable using data from upper-division physics students at multiple institutions. Overall, the work described in this thesis represents a significant contribution to the methodological tools available to researchers and instructors interested in improving student learning at the upper-division level.