This research focuses on the application of guided waves techniques to nondestructively characterize the structural integrity of bonded engineering components. Computational methods are used to examine the properties of multi-layered, adhesive bonded plates. This study quantifies the effect of the adhesive bond parameters (Young's modulus, Poisson's ration and bond thickness) on the dispersion curves. A commercial finite element (FE) code (ABAQUS/Explicit) is used for the numerical model while the global matrix method and the waveguide FE method are used to benchmark the resulting dispersion relationships in the form of a frequency-wavenumber or slowness-frequency relation. The postprocessing of FE data includes the two-dimensional Fourier transform (2D-FFT) and the short-time Fourier transform (STFT). Note that the 2D-FFT and STFT operate on multiple or just one transient output signals of the FE results respectively, while the waveguide FE method uses mass-, damping- and stiffness-matrices to generate the dispersion relations. In the dispersion relations, a set of bond parameter sensitive and FE-visible points is selected. The frequency locations of these points represent the solution criteria for the inversion procedure based on the global matrix method. The capabilities of the inversion process depend on the number of transient output signals from an FE simulation for the forward problem.

The advent of the internet has revolutionized the way people buy and sell. The internet is characterized by increased access to information. This increased information should foster convergence to the “law of one price,” for homogenous goods. The surge of electronic markets has motivated a stream of research focusing on comparing the efficiency of the internet market to the traditional one. This dissertation contributes to the existing literature of consumer search behavior in electronic markets and its effects on the price level and dispersion in the market more generally. A part of this dissertation assesses the direct and indirect effect of increased internet usage on the prices of airline tickets, using a unique contemporaneous online and offline transaction data for airline tickets, covering the final quarter of 2004. The study also investigates the relationship between increased internet usage and price dispersion in the market for airline tickets. This study also includes an exhaustive set of controls for airline ticket characteristics, namely refundability, advance purchase requirements, travel and stay restrictions, class of travel, departure and return day of the week and time, flight level load factor along with other market structure data used in the standard airlines literature. The existing theoretical literature in consumer search extended to the electronic markets assumes, for simplicity, that all consumers in the internet markets are the “searchers,” looking for the lowest price. The internet, however, also plays the role of a convenient shopping medium for a group of consumers whose primary motivation is not to search for the lowest price. The contemporary literature incorrectly categorizes these consumers as the traditional searchers. The remaining part of this dissertation provides a modification to the existing theoretical models of consumer search to accommodate both searchers and non-searchers in each of the electronic and traditional markets and derive the implications of the increased internet usage on the average level of prices and price dispersion in a market selling a homogenous good.

Reproduction de : Thèse de doctorat : Sciences de la Terre et des planètes solides : Toulouse, INPT : 2008. / Titre provenant de l'écran-titre. Bibliogr. 165 réf.

Thèse de doctorat : Sciences physiques et de l'ingénieur. Mécanique : Bordeaux 1 : 2008. / Titre provenant de l'écran-titre.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

Abstract Matrix solid-phase dispersion and gas chromatography-mass spectrometry were used for the rapid screening of 36 pesticides in agricultural products. Homogenized sample (0.5 g), C8-modified silica (0.5 g) and Na2SO4 (1 g) were mixed and transferred to a cartridge containing activated silica (0.5 g). Best recoveries (>60%) were found using dichloromethane-ethyl acetate (4:1) for elution. Analytical characteristics at spiking levels (10–100 lg/kg) were calculated for each pesticide. Matrix effects were studied by comparing the slopes of the matrix-matched calibration curves. Fruit and vegetable samples from South Africa complied with EU and South African current regulation, except for cypermethrin in green beans.

In vivo monitoring of mouse models of colon cancer promises to reduce the cost of research by improving sacrifice timing and allowing serial studies that observe the progression of disease and drug efficacy in a relatively small set of animals. Optical coherence tomography (OCT) is an optical analog of ultrasound imaging, capable of minimally-invasive mapping of light scatter intensity up to 2 mm deep in tissue. In this work, factors limiting resolution in OCT were examined and devices were created and applied to mouse colon imaging that extended the state-of-the-art in endoscopic ultrahigh-resolution OCT. First, axial chromatic aberration of the objective optics acts as a spectral filter in the sample arm limiting the effective bandwidth of the system. An achromatized endoscope design was demonstrated that achieved axial resolution of 2.3 mum in tissue and 4.4 mum lateral spot diameter with 101 dB sensitivity when interfaced with a time domain OCT system utilizing a 10-femtosecond laser (bandwidth=150 nm FWHM, center wavelength=800 nm). Second, dispersion matching between the sample and reference arms presents the practical resolution limit to endoscopic implementations including a separate, fiber-based reference arm. A second endoscope incorporated the reference arm into the tip of the endoscope using a novel custom beamsplitter prism and achieved 2.4 mum axial resolution in tissue without adjustments for pathlength or dispersion matching when interfaced with a spectrometer-based frequency domain OCT system and a similar laser. Third, non-linear dispersion of the sample media with respect to wavelength causes distortion and broadening of the axial point spread function when data are sampled uniformly in optical frequency. An experiment was performed on high dispersion glass to demonstrate that dispersion artifact free imaging can be achieved without post process corrections if the samples are acquired at equal intervals of media index of refraction divided by vacuum wavelength. Finally, other microscopic modalities that depend on tissue scatter intensity are used to find the origins of scatter in the mouse colonic mucosa. These observations are used to explain unexpected features found in ultrahigh-resolution tomograms collected with the two endoscopes presented.

No description available.

The use of chemicals to disperse oil spills raises concerns for organisms living below the surface of the water. While decreasing the surface area of the slick, chemical dispersants increase the amount of oil in the water column, the surface-to-volume ratio of droplets, the partitioning to water of the toxic constituents of oil, and the bioavailability of oil to pelagic and benthic organisms. Chemical dispersion can increase the exposure to polycyclic aromatic hydrocarbons (PAH) by 100-fold. As a model for a full-scale spill at sea, a wave tank was used to simulate chemical and natural dispersion of spilled oil to determine if the concentrations of chemically dispersed oil were sufficient to cause toxicity to embryos of Atlantic herring (Clupea harengus). While the hydrocarbon concentrations of dispersed oil from the wave tank were not large, the exposure response relationship was consistent with that of laboratory-prepared dispersed oil. Additionally, the toxicities of chemically dispersed oil prepared in the lab to Pacific (Clupea pallasi) and Atlantic herring were compared to ensure that the wealth of literature available on Pacific herring could be used for assessing the risk of oil exposure to Atlantic herring. Exposures to low concentrations of dispersed oil for short periods (2.4 to 24 h) consistently increased the incidence of blue sac disease, and decreased the percentage of normal embryos at hatch, indicating that even brief exposures to oil could be detrimental to the survival and recruitment of herring. / Thesis (Master, Biology) -- Queen's University, 2011-05-06 16:59:51.507

No description available.