Browsing by Subject "Reflectance"
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Item Development and use of a duststorm simulation chamber to evaluate solar concentrator degradation as characterized by loss in reflectivity(Texas Tech University, 1980-12) Collier, Elwin GreggNot availableItem Development of an improved, accelerated test for the effect of blowing dust on the service-life of solar collectors(Texas Tech University, 1985-12) Cooper, Austin MNot availableItem Engineering analysis of site-dependent factors affecting the Crosbyton solar power project(Texas Tech University, 1973-12) Barriger, Mark ThomasNot availableItem Experimental studies of high energy density silicon using ultra-fast lasers(2007) Grigsby, Will Robert, 1978-; Ditmire, Todd R.Understanding material behavior under extreme conditions is an important area of research in physics and material science. One method to study the behavior of materials under these conditions is to drive a strong shock wave through a material and watch its response. In many cases the material response is complicated by phase transitions such as lattice restructuring (Barker 1975; Mabire and Hereil 2000; Swift, Tierney et al. 2005) and melting (Asay 1975; Elias, Chapron et al. 1988; Werdiger, Eliezer et al. 1999; Mabire and Hereil 2000; Swift, Tierney et al. 2005). To study these dynamics we are using lasers in high time resolution pump-probe experiments to develop a real time diagnostic on the phase of a shocked material. This technique enables probing of the entire phase history of a material as it shock compresses and releases. In addition to linear reflectivity and ultra-fast 2D displacement interferometry, we developed a melting diagnostics based on the non-linear optical technique of third harmonic generation (THG) using a circularly polarized laser pulse. This diagnostic resolves the less than 300 fs melting transition of laser excited Si and GaAs, and it also detects a response in shock compressed silicon. Our results show that Si remains crystalline during compression of an elastic 100 kbar shock wave. Results from Si shocked to higher pressures (> 300 kbar) indicate a decrease in THG, suggesting some level of disordering or unexplained phase change.Item Hyper-spectral diffuse reflectance spectroscopy imaging towards the identification of non-melanoma skin cancers(2013-05) Bish, Sheldon Floyd; Tunnell, James W.Non-melanoma skin cancer is the most prevalent malignancy in the world, with over a million annual positive diagnoses in the United States. If left untreated, these cancers cause morbidity and in rare cases, can become life threatening. The key to identifying and characterizing these tumors in the earliest stages, where they are most treatable lie in margin delineation in order to prevent recurrence. The visual obscurity of tumor morphology and physiology can make early detection a difficult task for dermatologists, particularly in the initial stages of cancer development. Tumor resection is a common course of action once they are discovered; however, there is a high recurrence rate due to incomplete removal of the malignant tissue. This dissertation presents an imaging system that can capture the spectral signatures correlating with morphological and physiological changes that accompany skin dysplasia. With this system, we may improve tumor margin delineation, reducing the number of incomplete tumor biopsies and false negative screenings. As an initial step of this process, we begin with a non-contact point sampling diffuse reflectance probe that mitigates the adverse effects of traditional contact probing. Validation of this probe is performed using tissue simulating phantoms spanning a biologically relevant range of optical and physiological properties to ensure that the non-contact format will not hinder performance relative to the contact probe. Cross polarization and auto-focus mechanisms were included in the design to reduce specular reflections and movement artifacts from in vivo measurements. This non-contact design was further developed into a platform for investigating the role of sampling geometry on diffuse reflectance measurements with the addition of a DMD spatial filter. Finally, we developed a hyperspectral DRSi system for the acquisition of wide-field maps of optical and physiological properties that is currently being tested on patients undergoing skin cancer screenings. The spectral output of this system has been validated for scattering and absorption across biologically relevant ranges using tissue simulating phantoms. The DRSi system was optimized for portability, ergonomics and resolution.Item Polarization sensitive optical coherence tomography for primate retinal evaluation in a longitudinal glaucoma study(2011-12) Dwelle, Jordan Charles; Rylander, H. Grady (Henry Grady), 1948-; Milner, Thomas E.A polarization sensitive optical coherence tomography (PS-OCT) instrument is presented for the study of glaucoma. Glaucoma is the second leading cause of blindness worldwide and causes irreversible damage to the retina. This PS-OCT system was built to perform retinal imaging with a swept source laser providing a 28 kHz A-scan repetition rate. Thickness, phase retardation, birefringence and reflectance index measurements were taken from the primate eyes on a weekly or semi-weekly basis through the course of a 30 week study. Statistical analysis of these measurements indicates that the reflectance index is the earliest measured indicator of glaucomatous changes and a potential marker for early glaucoma diagnosis.Item Solar reflectivity and absorptivity studies(Texas Tech University, 1978-05) Chin, ShaulongNot availableItem Use of spectral analysis to distinguish wheat from barley(Texas Tech University, 1985-05) Jaspers, James GordonNot available