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Thesis (M.S.)--Rutgers University, 2008. / "Graduate Program in Mechanical and Aerospace Engineering." Includes bibliographical references (p. 63-67).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 223-242). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 87-91). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 113-118). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (p. 105-107).

In this dissertation, I have investigated applying the laser ablation of microparticle aerosol (LAMA) process to the production of nanocomposite polymer membranes for olefin/paraffin separation. Experimental results for three major thrusts are presented: 1) an investigation into the scalability of the LAMA process, 2) a new laser ablation technique for nanoparticle production from aqueous feedstocks, and 3) characterization of olefin-selective polymer nanocomposite membranes produced using LAMA. The propensity for Ag nanoparticles to form agglomerates in LAMA is investigated. Nanoparticle samples were collected on TEM grids at several feedstock aerosol densities. As the density increased, the particle morphology shifted from single nanoparticles 5 nm in diameter to chained agglomerates of 20 nm diameter primary particles. The results are in agreement with a numerical model of Brownian agglomeration and diffusion. Factors influencing nanoparticle morphology, such as temperature, initial nanoparticle charge, and feedstock aerosol density are discussed. It is shown that agglomeration occurs on a much longer timescale than the other processes, and can be treated independently. A new nanoparticle synthesis technique is presented: laser ablation of aqueous aerosols. A Collison nebulizer is used to generate a mist of ~10 [mu]m diameter water droplets containing dissolved transition metal salts. Water from the droplets quickly evaporates, leaving solid particles which are ablated by an excimer laser. Ablation results in plasma breakdown and photothermal decomposition of the feedstock material. For AgNO₃ ablated in He gas, metallic Ag nanoparticles were produced. For Cu(NO₃)₂ ablated in He gas, crystalline Cu₂O nanoparticles were produced. For Ni(NO₃)₂ ablated in He gas, crystalline NiO nanoparticles were produced. A combination of AgNO₃ and Cu(NO₃)₂ ablated in a reducing atmosphere of 10%H₂/He yielded nonequilibrium Ag-Cu alloy nanoparticles. Membranes composed of poly(ethylene glycol diacrylate) (PEGDA) and Ag nanoparticles were produced by the LAMA process. Permeation and sorption measurements for the light olefins and paraffins were conducted for these membranes. The membranes showed very little improvement in olefin/paraffin selectivity compared with neat PEGDA membranes. Using the LAMA implementation described here, it was impossible to produce membranes with high Ag loading. Whether membranes containing more Ag would exhibit improved selectivity remains an open question. / text

The coupled effects of thermochemical and thermomechanical erosion are investigated. A quasi-steady ablation model with finite rate surface chemistry is developed and applied to a solid carbon combustion scenario to investigate the system’s behavior in situations in which surface reactions are not in equilibrium. It is found that in this regime, the system can be described effectively in terms of the B number and the Damkohler number, and a useful algebraic relationship between these parameters is determined for nonequilibrium behavior. The thermochemical ablation model is then expanded by considering mechanical removal of thermochemically weakened material from the ablating surface. A model is developed for a randomly oriented carbon fiber preform material, like that used in the production of phenolic impregnated carbon ablator (PICA), and this model is incorporated into the previously developed ablation code. It is found that for PICA in realistic reentry scenarios, the removal of individual fibers from the ablating surface by mechanical erosion is not an important mass loss mechanism, although hypothetical situations exist where this mechanism for mechanical removal of material is non-negligible. The thermo-chemo-mechanical erosion mechanism is then extended to address brand generation in wildland fire scenarios. A model is developed to predict the size and number distribution of embers generated from a tree with fractal geometry. This model is coupled to a simple plume and propagation model similar to those existing in the literature, and a case study is performed for a realistic wildfire scenario. The presence of an optimal branch diameter for brand propagation is identified, and areas for future work in thermo-chemo-mechanical degradation are discussed. / text

Radiofrequency ablation (RFA) is a clinic tool for the treatment of various target tissues. However, one of the major limitations with RFA is the ‘small’ size of target tissues that can be effectively ablated. By small it is meant the size of the target tissue is less than 3 cm in diameter of the tissue otherwise ‘large’ size of tissue in this thesis. A typical problem with RFA for large target tissue is the incompleteness of tumour ablation, which is an important reason for tumour recurring. It is widely agreed that two reasons are responsible for the tumour recurring: (1) the tissue charring and (2) the ‘heat-sink’ effect of large blood vessels (i.e. ≥3 mm in diameter). This thesis study was motivated to more quantitatively understand tissue charring during the RFA procedure and to develop solutions to increase the size of target tissues to be ablated. The thesis study mainly performed three tasks: (1) evaluation of the existing devices and protocols to give a clear understanding of the state of arts of RFA devices in clinic, (2) development of an accurate mathematical model for the RFA procedure to enable a more quantitative understanding of the small target tissue size problem, and (3) development of a new protocol based on the existing device to increase the size of target tissues to be ablated based on the knowledge acquired from (1) and (2). In (1), a design theory called axiomatic design theory (ADT) was applied in order to make the evaluation more objective. In (2), a two-compartment finite element model was developed and verified with in vitro experiments, where liver tissue was taken and a custom-made RFA system was employed; after that, three most commonly used internally cooled RFA systems (constant, pulsed, and temperature-controlled) were employed to demonstrate the maximum size of tumour that can be ablated. In (3) a novel feedback temperature-controlled RFA protocol was proposed to overcome the small target tissue size problem, which includes (a) the judicious selection of control areas and target control temperatures and (b) the use of the tissue temperature instead of electrode tip temperature as a feedback for control. The conclusions that can be drawn from this thesis are given as follows: (1) the decoupled design in the current RFA systems can be a critical reason for the incomplete target tissue necrosis (TTN), (2) using both the constant RFA and pulsed RFA, the largest TTN can be achieved at the maximum voltage applied (MVA) without the roll-off occurrence. Furthermore, the largest TTN sizes for both constant RFA and pulsed RFA are all less than 3 cm in diameter, (3) for target tissues of different sizes, the MVA without the roll-off occurrence is different and it decreases with increase of the target tissue size, (4) the largest TTN achieved by using temperature-controlled RFA under the current commercial protocol is still smaller 3 cm in diameter, and (5) the TTN with and over 3 cm in diameter can be obtained by using temperature-controlled RFA under a new protocol developed in this thesis study, in which the temperature of target tissue around the middle part of electrode is controlled at 90 ℃ for a standard ablation time (i.e. 720 s). There are a couple of contributions with this thesis. First, the underlying reason of the incomplete TTN of the current commercially available RFA systems was found, which is their inadequate design (i.e. decoupled design). This will help to give a guideline in RFA device design or improvement in the future. Second, the thesis has mathematically proved the empirical conclusion in clinic that the limit size of target tissue using the current RFA systems is 3 cm in diameter. This has advanced our understanding of the limit of the RFA technology in general. Third, the novel protocol proposed by the thesis is promising to increase the size of TTN with RFA technology by about 30%. The new protocol also reveals a very complex thermal control problem in the context of human tissues, and solving this problem effectively gives implication to similar problems in other thermal-based tumour ablation processes.

In this dissertation, I will look into the size distribution of silver nanoparticles produced by laser ablation of microparticles (LAM). I will investigate the role of both pulsed and continuously operating nozzles on the size distribution. In addition, I will examine any deviations from the previously observed log-normal size distribution for silver nanoparticles comparing previous collection techniques involving supersonic jet impaction with a current time of flight mass spectrometer (TOF-MS). These new observations will be made in situ using a Wiley-McLaren TOF-MS with a reflector and multiphoton ionization and will mainly focus on the smaller sized nanoparticles. An introduction to enhancing a second harmonic optically generated signal will also be investigated involving silver nanocomposites while utilizing a polarized crossed-beam femtosecond laser technique. / text