The 60 kev x-rays from Americium-241 (241Am) have been used in an x-ray attenuation experiment to measure the thickness and attenuation coefficient of an aluminum alloy. Using traditional measurement tools such as a micrometer, to determine the thickness and uniformity of soft metal targets and curved aluminum target cell windows is challenging. Furthermore, the determination of window thickness is important to Jefferson Lab experiments, in particular the Qweak experiment. In this thesis, the thickness of Aluminum foil AL7057 is determined with high accuracy using x-ray attenuation. Using the x-ray attenuation technique has the advantage of nondestructive measurement.

The potential for biodegradation of contaminants in soil was assessed using an array of molecular methods, including terminal restriction fragment length polymorphism (TRFLP), quantitative polymerase chain reaction (qPCR), and traditional culturing techniques combined with sequencing of the 16S or ITS regions of the cultured bacteria and fungi. Soil was collected from the Santa Susana Field Laboratory (SSFL), which was the site of numerous liquid-propulsion rocket engine tests as well as nuclear energy research and development, which led to contamination of the soil with a wide variety of constituents. The contaminants of interest (COIs) at this site include polychlorinated biphenyls (PCBs), dioxins, polycyclic aromatic hydrocarbons (PAHs) and non-PAH petroleum hydrocarbons (PHCs). Various metals, most notably mercury and silver, are also present on the site. The purpose of this study was to determine if biodegradation is contributing to natural attenuation of contaminants in the soil, what organisms are likely causing biodegradation, and what rate(s) can be expected in the future. A literature review was conducted to investigate the chemical properties of theses COIs, their toxicity, and abiotic and biotic degradation. This research concluded that these COIs can be biodegraded if the right bacteria and/or fungi are present and active in the soil in sufficient numbers under the right conditions. Many known biodegraders of the COIs were identified in the literature review along with the most common pathways of biodegradation and degradation rates observed in field and laboratory studies. Soil was collected from 30 sample locations, with 3 sets of 10 samples containing high concentrations of one COI but low concentration of the others. PHCs and PAHs were found to be largely co-located, so 10 samples were selected for both of them. The remaining 20 samples were split evenly between PCBs and dioxins. DNA was extracted directly from all 30 soil samples and amplified using PCR for TRFLP analyses. Two soil samples were sent to Microbial Insights® for qPCR analysis. This analysis included 18 gene targets for the degradation of PHCs and PAHs, as well as the target gene for Dehalococcoides (an anaerobic dechlorinating bacteria). For each culturing a model chemical was selected to represent each COI and added to Bushnell-Haas agar plates containing no added carbon source other than the model compounds. The model chemicals were No. 2 diesel fuel for PHCs, naphthalene for PAHs, PCB #1 (monochloro) for PCBs, and dibenzofuran for dioxin. These plates were used to screen for biodegrading bacteria and fungi for each COI. Once cultured, 16S and ITS sequencing were used to identify these potential COI degraders and determine what TRFLP peak they would produce. The identity of isolated organisms was compared to information from the literature to assess the likelihood of COI biodegradation at SSFL. From the culturing experiments, 45 organisms were isolated, sequenced, and identified. The 45 included 14 unique bacteria and seven unique fungi. Of these, 10 different bacterial species and 5 different fungal species have been reported as COI biodegraders or belong to genera that contain reported COI biodegraders. TRFLP analysis revealed that the soil type has more effect on the microbial population than the presence of any of the COIs. There were no specific peaks that were significantly correlated to any specific COI. The peak distributions were fairly even, indicating a large amount of biodiversity in the microbial populations of the soil samples. The qPCR analysis revealed that SSFL soils contain significant populations of microbes that can degrade PHCs aerobically. Anaerobic PHC, anaerobic PAH, and aerobic PAH targets were not detected. A small amount of Dehalococcoides was detected in one of the samples. Collectively this study suggests that microbes present in SSFL soils are capable of biodegrading PHCs, and the genes for such biodegradation are actively being expressed. With the exception of a small population of Dehalococcoides, bacteria associated with the biodegradation of PAHs, PCBs, and/or dioxins were not detected. However, several strains of fungi were identified which have been reported to mediate cometabolic biodegradation of these compounds. Since these fungi do not require anaerobic conditions, they are more likely to contribute to natural attenuation than bacterial reductive dechlorination. Laboratory microcosm experiments are suggested for estimating rates of biodegradation at SSFL under natural attenuation conditions. Bioaugmentation and/or biostimulation methods should also be investigated in addition of natural attenuation. These microcosm experiments are currently underway in a companion study at Cal Poly by graduate student Mackenzie Billings.

<p> Optical fibers are becoming so good that their optical and mechanical properties are fast approaching fundamental limits. It has also become evident that there is a requirement for establishing accurate and precise measurement techniques of these properties. The optical loss is the most important parameter characterizing fiber. This project reviews the subject of loss (or attenuation), its measurement and some of its subtleties. </p> <p> Presently at BNR there are two attenuation measurements made: (1) one is the LED steady-state attenuation at λ≅840 nm, which makes use of a "pigtail" launching fiber and (2) the second is the spectral attenuation from 600-1400 nm. Both measurement techniques were developed by the author and Dr. K. Abe during the summer work term and made considerable improvements in both accuracy and speed over previously established methods. Some of the subtleties of attenuation which were also studied during this period were the effects of different launch conditions, and environmental effects such as those caused by temperature and ice. The extensive temperature tests done on the fiber led to the change from "hytrel" and nylon as coating materials to the use of silicone (which is still in use at BNR).</p> <p> Throughout the paper, results of the measurements have been given for several types of fibers because some of them have very unique characteristics and applications. </p> <p> All of the data displayed for this project was gathered by the author unless otherwise noted.</p> / Thesis / Master of Engineering (MEngr)

<p> In six conditioned suppression experiments with rats, two conditioned stimuli (CSs) were individually trained and then tested as a compound. In one set of experiments, the suppressing effect of the compound was greater than that of either CS presented alone. This result is referred to as compound summation. In a second set of experiments, the suppressing effect of the compound was less than that of the "stronger" suppressing individual CS. This result is referred to as compound attenuation. The combination of summation and attenuation makes it possible to determine whether CSs with unknown properties are weakly excitatory (i.e., weak suppressors) or inhibitory (i.e., conditioned characteristics that are opposite the excitatory suppressing effect). If an unknown CS is tested in compound with a second CS known to be excitatory, summation indicates that the unknown stimulus is excitatory, while attenuation indicates that the unknown stimulus is inhibitory. In a final set of experiments, this compound test procedure was used to examine extinction and differential conditioning as inhibitory training procedures. Extensive extinction of a previously trained CS, even far beyond the point at which suppression vanished, was found to be an ineffective inhibitory training procedure. Rather, compound tests showed that the stimulus retained excitatory properties. Differential conditioning was found to be a very effective inhibitory training procedure, regardless of whether presentations of a previously trained CS and shock, shook alone, or the previously trained CS - alone accompanied the unreinforced CS undergoing inhibitory conditioning. These findings are discussed in terms of current theories of conditioning and unresolved issues surrounding the acquisition and maintenance of inhibitory properties.</p> / Thesis / Doctor of Philosophy (PhD)

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A bulk of the research on piezoelectric systems in recent years can be classified into two categories, 1) studies of linear piezoelectric oscillator arrays, 2) studies of nonlinear piezoelectric oscillators. This dissertation derives novel linear and nonlinear modeling and estimation methods for such piezoelectric systems. In the first part, this work develops modeling and design methods for Piezoelectric Subordinate Oscillator Arrays (PSOAs) for the wideband vibration attenuation problem. PSOAs offer a straightforward and low mass ratio solution to cancel out the resonant peaks in a host structure's frequency domain. Further, they provide adaptability through shunt tuning, which gives them the ability to recover performance losses because of structural parameter errors. This dissertation studies the derivation of governing equations that result in a closed-form expression for the frequency response function. It also analyzes systematic approaches to assign distributions to the nondimensional parameters in the frequency response function to achieve the desired flat-band frequency response. Finally, the effectiveness of PSOAs under ideal and nonideal conditions are demonstrated in this dissertation through extensive numerical and experimental studies. The concept of performance recovery, introduced in empirical studies, gives a measure of the PSOA's effectiveness in the presence of disorder before and after capacitive tuning. The second part of this dissertation introduces novel modeling and estimation methods for nonlinear piezoelectric oscillators. Traditional modeling techniques require knowledge of the structure as well as the source of nonlinearity. Data-driven modeling techniques used extensively in recent times build approximations. An adaptive estimation method, that uses reproducing kernel Hilbert space (RKHS) embedding methods, can estimate the underlying nonlinear function that governs the system's dynamics. A model built by such a method can overcome some of the limitations of the modeling approaches mentioned above. This dissertation discusses (i) how to construct the RKHS based estimator for the piezoelectric oscillator problem, (ii) how to choose kernel centers for approximating the RKHS, and (iii) derives sufficient conditions for convergence of the function estimate to the actual function. In each of these discussions, numerical studies are used to show the RKHS based adaptive estimator's effectiveness for identifying linearities in piezoelectric oscillators. / Doctor of Philosophy / Piezoelectric materials are materials that generate an electric charge when mechanical stress is applied, and vice versa, in a lossless transformation. Engineers have used piezoelectric materials for a variety of applications, including vibration control and energy harvesting. This dissertation introduces (1) novel methods for vibration attenuation using an array of piezoelectric oscillators, and (2) methods to model and estimate the nonlinear behavior exhibited by piezoelectric materials at very high mechanical forces or electric charges. Arrays of piezoelectric oscillators attached to a host structure are termed piezoelectric subordinate oscillator arrays (PSOAs). With the careful design of PSOAs, we show that we can reduce the vibration of the host structure. This dissertation analyzes methodologies for designing PSOAs and illustrates their vibration attenuation capabilities numerically and experimentally. The numerical and experimental studies also illustrate the robustness of PSOAs. In the second part of this dissertation, we analyze reproducing kernel Hilbert space embedding methods for adaptive estimation of nonlinearities in piezoelectric systems. Kernel methods are extensively used in machine learning, and control theorists have studied adaptive estimation of functions in finite-dimensional spaces. In this work, we adapt kernel methods for adaptive estimation of functions in infinite-dimensional spaces that appear while modeling piezoelectric systems. We derive theorems that ensure convergence of function estimates to the actual function and develop algorithms for careful selection of the kernel basis functions.

Circumaural ear cups have been used for decades as an effective way of protecting users from high noise fields. Over the decades, a number of researchers dedicated their time to understanding the dynamics that govern the attenuation of hearing protectors. This thesis duplicates some of this work with newer technology and better data processing ability. In addition to revitalizing the accepted knowledge of hearing protector technology, this thesis is the first documented effort to show how the previously ignored air leak, known to exist between the ear cup and the head, has a profound effect on the low and mid frequency attenuation of a circumaural hearing defender. Past research focused on the mechanical vibration of the cup on the seal as the main source of noise within the ear cup. This mechanical vibration, known as the piston resonance exists, and affected noise attenuation within the ear cup. A reasonably sized air leak of 160 e-7 m2 however, overwhelmed the piston resonance. An air leak of this size was shown to degrade noise attenuation by over 50 dB at 40Hz and 30 dB at 200 Hz when compared to a no-leak case. Further testing also suggested that the air leak has the ability to continue adding energy into the cup up to 3000 Hz. / Master of Science

Noise levels in areas adjacent to high performance jets have increased monotonically in the past few years. When personnel are exposed to such high noise fields, the need for better hearing protection is inevitable. Adequate hearing protection may be achieved through the use of circumaural ear defenders, earplugs or both. This thesis focuses on identifying the dominant physical phenomena, responsible for the low frequency (0 – 300 Hz) acoustic response inside the earmuffs. A large volume earcup is used with the undercut seal for the study. The significance of this research is the use of finite element methods in the area of hearing protection design. The objectives of this research are to identify the dominant physical phenomena responsible for the loss of hearing protection in the lower frequency range, and develop FE models to analyze the effects of structural and acoustic modes on the acoustic pressure response inside the earcup. It is found that there are two phenomena, which are primarily responsible for the lower frequency acoustic response inside the earmuffs. These modes are recognized in this thesis as the piston mode and the Helmholtz mode. The piston mode occurs due to the dynamics of the earcup and seal at 150 Hz, which results in loss of hearing protection. The Helmholtz mode occurs due to the presence of leaks. The resonant frequency of the Helmholtz mode and the pressure response depends on the leak size. / Master of Science

Permeable reactive barrier (PRB) technology is increasingly considered for in situ treatment of contaminated groundwater; however, current design formulas for PRBs are limited and do not properly account for all major physical and attenuation processes driving remediation. This study focused on developing a simple methodology to design PRBs that is easy to implement while improving accuracy and being more conservative than the available design methodologies. An empirical design equation and a simple analytical design equation were obtained to calculate the thickness of a PRB capable of degrading a contaminant from a source contaminant concentration to a maximum contaminant level at a Point of compliance . Both equations integrate the fundamental components that drive the natural attenuation process of the aquifer and the reactive capacity of the PRB.The empirical design equation was derived from a dataset of random hypothetical cases that used the solutions of the PRB conceptual model (Solution I). The analytical design equation was derived from particular solutions of the model (Solution II) which the study showed fit the complex solutions of the model well. Using the hypothetical cases, the analytical equation has shown that it gives an estimated thickness of the PRB just 15 % lower or higher than the real thickness of the PRB 95 percent of the time. To calculate the design thickness of a PRB, Natural attenuation capacity of the aquifer can be estimated from the observed contaminant concentration changes along aquifer flowpaths prior to the installation of a PRB. Bench-scale or pilot testing can provide good estimates of the required residence times ( Gavaskar et al. 2000) , which will provide the reactive capacity of the PRB needed for the calculation. The results of this study suggest also that the installation location downgradient from the source of contaminant is flexible. If a PRB is installed in two different locations, it will achieve the same remediation goals. This important finding gives engineers and scientists the choice to adjust the location of their PRBs so that the overall project can be the most feasible and cost effective. / Master of Science