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Accurate attenuation correction is essential for quantitative positron emission tomography. Typically, this correction is based on a coincidence transmission measurement using an external source of positron emitter, which is positioned close to the detectors. This technique suffers from poor statistical quality and high dead time losses, especially with a high transmission source strength. We have proposed and tested the use of single photon transmission measurement with a rotating rod source, to measure the attenuation correction factors (ACFs). The singles projections are resampled into the coincidence geometry using the detector positions and the r,)d source location. A nonparalyzable dead time correction algorithm was developed for the block detectors used in the McMaster PET scanner. Transaxial resolution is approximately 6 mm, which is comparable to emission scanning performance. Axial resolution is about 25 mm, with only crude source collimation. ACFs are underestimated by approximately 10% due to increased crossplane scatter, compared to coincidence transmission scanning. Effective source collimation is necessary to obtain suitable axial resolution and improved accuracy. The response of the correction factors to object density is linear to within 15%, when comparing singles transmission measurement to current coincidence transmission measurement. The major advantage of using singles transmission measurement IS a dramatically increased count rate. A factor of seven increase in count rate over coincidence scanning is possible with a 2 mCi transmission rod source. There are no randoms counted in singles transmission scans, which makes the measured count rate nearly linearly proportional with source activity. Singles detector dead time is approximately 6% in the detectors opposite a 2 mCi rod source. Present hardware and software precludes the application of this technique in a clinical environment. We anticipate that real time acquisition of detector singles can reduce the transmission scanning time to under 2 minutes, and produce attenuation coefficient images with under 2% noise. This is a significant improvement compared to the current coincidence transmission technique. / Thesis / Master of Science (MS)

Development of a scientific basis for management of uranium bearing wastes and contaminants requires information from natural geologic systems. The following study of the Coles Hill uranium deposit and associated weathered zone constrains processes leading to the natural attenuation of uranium within an oxidizing, fluid rich environment typical of the eastern US. At the Coles Hill deposit fracture hosted, primary U(IV) bearing mineral assemblages formed during hydrothermal activity associated with Mesozoic faulting. The most abundant ore assemblage consists of coffinite and apatite, but uraninite-zeolite and uraninite-calcite assemblages are also present. Within the shallow bedrock there is a uranium redox transition where alteration of U(IV) minerals has produced secondary uranium minerals. Geochemical data suggests that the volume of rock containing this U(IV)/U(VI) transition is acting as a closed system with respect to uranium mass transport during oxidation. The dominant mechanism of uranium fixation within the oxidizing zone is the precipitation of Ba-U(VI) phosphates (meta-autunite group). Speciation and mineral stability calculations indicate that ground waters from the Coles Hill weathered zone are saturated with respect to Ba-meta-autunite and that this mineral is capable of buffering dissolved uranium concentrations to values lower than 20 parts per billion. U(VI) phosphates of the meta-autunite group are not stable in the vadose zone (soil pH ~ 4.5) at the Coles Hill site. In this zone uranium is associated with (Ba, Ca, Sr) aluminum phosphate of the crandallite group as well as with phosphate sorbed to iron oxy-hydroxide mineral coatings. Uranium leached from the vadose zone is reprecipitated as new meta-autunite minerals below the water table due to higher pH conditions of ~6.0 and relatively high activity ratios of dissolved phosphate to carbonate (e.g. log [H2PO4-/HCO3-] > -3). It is estimated that the U(VI) phosphates responsible for the natural attenuation of uranium at this site persist within the weathering zone for hundreds of thousands of years. Thus, the Coles Hill deposit represents an excellent natural laboratory for the study of uranium attenuation with potential applications for the design and implementation of cost effective remediation and containment strategies, such as soil amendments techniques and in-situ reactive barriers technologies. / Ph. D.

Natural Attenuation Software (NAS) was developed as a screening tool to estimate remediation timeframes for monitored natural attenuation (MNA) to lower groundwater contaminant concentrations to regulatory limits, and to assist in decision-making on the level of source zone treatment in conjunction with MNA using site-specific remediation objectives. In addition, NAS facilitates the combined use of MNA with engineered remedial actions (ERAs) so that the benefits of each technology can be maximized while minimizing costs of remediation. The primary expected benefit of NAS is to increase regulatory acceptance of MNA, thereby decreasing overall remediation costs. NAS is designed for application to ground-water systems consisting of porous, relatively homogeneous, saturated media, and assumes that groundwater flow is uniform and unidirectional. NAS consists of a combination of analytical and numerical solute transport models implemented in three main interactive modules to provide estimates for: (1) target source concentration required for a plume extent to contract to regulatory limits, (2) time required for NAPL contaminants in the source area to attenuate to a predetermined target source concentration, and (3) time required for a plume extent to contract to regulatory limits after source reduction. Natural attenuation processes that NAS models include advection, dispersion, sorption, non-aqueous phase liquid (NAPL) dissolution, and biodegradation. NAS determines redox zonation, and estimates and applies varied biodegradation rates from one redox zone to the next. Recently, NAS was enhanced to include petroleum hydrocarbons, chlorinated ethenes, chlorinated ethanes, chlorinated methanes, and chlorinated benzenes, or any user-defined contaminants (e.g., heavy metals, radioisotopes), and has included the capability to model co-mingled plumes. To enable comparison of remediation timeframe estimates between MNA and specific ERAs, NAS was modified to incorporate an estimation technique for timeframes associated with pump-and-treat remediation technology for comparison to, or in conjunction with, MNA. NAS also expanded analysis tools for improved performance assessment, as well as the assessment of sustainability of natural attenuation processes over time. A Department of Defense (DoD) Environmental Security Technology Certification Program (ESTCP) demonstration was undertaken to evaluate the capability of the NAS software to provide reasonable estimates of MNA cleanup timeframes in a variety of environments and sites throughout the United States. Overall, results suggest that NAS was satisfactory in meeting performance objectives set forth in the demonstration, and that because NAS is based on sound science, it can serve as an effective tool for decision-making and data analysis at a wide range of contaminated sites and is not limited to a small subset of “simple sites” because of its simplicity. At some sites, NAS-estimated timeframes were crucial for winning regulatory acceptance of MNA, with cost-benefit analyses providing estimates of savings associated with using MNA as a final remediation strategy. / Ph. D.

Radio Tomographic imaging (RTI) is an exciting new field that utilizes a sensor network of a large number of relatively simple radio nodes for inverse imaging, utilizing similar mathematical algorithms to those used in medical imaging. Previous work in this field has almost exclusively focused on device-free object location and tracking. In this thesis, the application of RTI to propagation problems will be studied-- specifically using RTI to measure the strength and location of attenuating objects in an area of interest, then using this knowledge of the shadowing present in an area for radio coverage prediction. In addition to radio coverage prediction, RTI can be used to improve the quality of RSS-based position location estimates. Because the traditional failing of RSS-based multilateration is ranging error due to attenuating objects, RTI has great potential for improving the accuracy of these estimates if shadowing objects are accounted for. In this thesis, these two problems will primarily be studied. A comparison with other inverse imaging, remote sensing, and propagation modeling techniques of interest will be given, as well as a description of the mathematical theory used for tomographic image reconstruction. Proof-of-concept of the efficacy of applying RTI to position location will be given by computer simulation, and then physical experiments with an RTI network consisting of 28 Zigbee radio sensors will be used to verify the validity of these assertions. It will be shown in this thesis that RTI does provide noticeable improvement in RSS-based position location accuracy in cluttered environments, and it produces much more accurate RSS estimates than a standard exponential path-loss model is able to provide. / Master of Science

Laboratory microcosm experiments were conducted to assess the potential for biostimulation and bioaugmentation as source reduction measures in support of a monitored natural attenuation remedial strategy at Naval Amphibious Base (NAB) Little Creek. Previous work with laboratory microcosms conducted under simulated natural (unamended) conditions has demonstrated that indigenous dehalorespirators were capable of partial dechlorination of tetrachloroethene (PCE) to cis-dichloroethene (cis-DCE). This study attempts to achieve complete reductive dechlorination with amendments to static microcosms to test the hypotheses that nutrient-limited or microorganism-limited conditions exist in aquifer sediments obtained from the site. The enhanced bioremediation experiments were comprised of nutrient-amended microcosms receiving additions of electron donors, mineral medium, or anaerobic digester supernatant, and dechlorinating culture-amended microcosms were inoculated with a culture capable of transforming PCE to ethene. Reductive dechlorination in the nutrient-amended microcosms proceeded to cis-DCE over a 260-day study period, at slightly higher rates than in experiments conducted with aquifer sediments from the same location under natural conditions. Inoculation of aquifer sediments with a small amount of dechlorinating culture initiated rapid transformation of PCE to vinyl chloride (VC) by day 18 of the study. Zero-order rates of PCE dechlorination in unamended, propionate-, formate-, mineral medium-, digester supernatant-, and dechlorinating culture-amended microcosms were 0.24, 0.750, 1.30, 0.339, 0.177, and 1.75 µM/day, respectively. The results of this study suggest that an engineered biostimulation approach alone may not be as beneficial for PCE source reduction at NAB Little Creek, than bioaugmentation with competent dehalorespirators, along with the inclusion of supplemental nutrients which would be available to stimulate dechlorination activity of both indigenous and introduced microorganisms. / Master of Science

The proposed use of communication satellites operating above 10 GHz has stimulated research into the effects of atmospheric rain and ice on the reception of these signals. This thesis examines the statistics of fade rate, fade duration, and interface intervals on 19 and 28 GHz communication links, at an elevation angle of 45 degrees. The study uses 2 years of data collected from the COMSTAR-D2 experimental propagation beacons at Blacksburg, Virginia. The results are shown to depend on frequency, elevation angle, time of year, rainrate, rainfall amount, and the signal polarization. The results are also shown to depend on the receiver time constants, the data acquisition system sampling rate, and the signal-to-noise ratio. The number of fade events and interface intervals was found to vary slightly when hysteresis was added to the data reduction program. / M.S.

[ES] Esta investigación tiene como objeto de estudio los mecanismos de atenuación empleados en la lengua oral china para contribuir con los estudios de lingüística conversacional china en un aspecto carente de estudios previos. Los objetivos principales del presente estudio son: 1) describir las características de los mecanismos de atenuación en chino. y 2) clasificar los mecanismos de atenuación que se utilizan en la lengua china oral. De ahí se desprenden cuatro objetivos específicos: 1) analizar de qué forma influye el contexto situacional y la cultura en el uso de las estrategias de atenuación en chino; 2) examinar las funciones de los mecanismos de atenuación; 3) explicar las características de los mecanismos de atenuación en los tipos de actos de habla y 4) identificar las características principales de los atenuantes en función de las variables género, edad y formación académica. Para cumplir con los objetivos planteados se ha elaborado un corpus formado por 14 conversaciones coloquiales que suman un total de 10 horas y 27 minutos de duración. Las relaciones que hay entre los interlocutores son de amistad y parentesco. La identificación de los mecanismos utilizados se realiza en base a la ficha metodológica de Albelda et al. (2014) A partir del análisis del corpus se han obtenido 21 tipos de mecanismos, cuyas características de uso evidencian el impacto cultural en ellas. Así mismo, se ha mostrado que la función por la que más se atenúa es la de prevención de amenazas a la imagen y, por la que menos, por la de reparación. Con respecto a los tipos de actos de habla, el asertivo es el que presenta un mayor número de uso de mecanismos de atenuación. Por último se ha mostrado que existen diferencias en el uso de los mecanismos de atenuación según las variables de género, edad y nivel de formación académica. / [CA] Aquesta tesi tracta d'investigar els mecanismes d'atenuació emprats en la llengua oral xinesa. Amb aquesta investigació es pretén contribuir en un camp que no té estudis d'aquests mecanismes en converses en llengua xinesa. Els objectius principals d'aquest estudi són: en primer lloc, classificar els mecanismes d'atenuació que s'utilitzen en la llengua xinesa oral, i en segon lloc, descriure les característiques d'aquests mecanismes d'atenuació. Es desprenen quatre objectius específics, que són: 1) analitzar si el context i la cultura influeixen en l'ús de les estratègies d'atenuació en xinès; 2) examinar les funcions dels mecanismes d'atenuació i la relació entre ells; 3) explicar les característiques dels mecanismes d'atenuació en els tipus d'actes de parla; i 4) identificar les característiques més freqüents lligades a les variables de gènere, edat i formació acadèmica. Per complir amb els objectius plantejats es va elaborar un corpus propi format per 14 converses col·loquials amb un total de 10 hores i 27 minuts de durada. Les relacions que hi ha entre els interlocutors són d'amistat o familiars. La identificació dels mecanismes utilitzats es realitza basant-se en la fitxa metodològica d'Albelda et al. (2014) A partir d'l'anàlisi s'han obtingut 21 tipus de mecanismes d'atenuació utilitzats en el corpus, les característiques de l'ús dels mecanismes van evidenciar l'impacte cultural en elles. així mateix, s'ha mostrat que la funció per la que més s'atenuen és la funció de prevenció d'amenaces a la imatge, i la que menys és la funció de reparació. Pel que fa als tipus d'acte de parla, en l'acte assertiu es presenta un major nombre de casos de mecanismes d'atenuació. Finalment s'ha mostrat que hi ha diferències en l'ús dels mecanismes d'atenuació segons el gènere, edat i nivell d'estudis. / [EN] This research addresses the issue of the usage of attenuation mechanism in oral Chinese. With this research we intend to contribute to fill in the gap of such studies in Chinese. The main objective of this research is to classify the attenuation mechanism used in oral Chinese language and to describe their characteristics. Four specific objectives include: 1) to analyze if the context and the culture influence the use of attenuation mechanism in Chinese; 2) to examine the functions of attenuation mechanism and the relationship between them; 3) to explain the characteristics of the attenuation mechanism in different types of speech act; and 4) to identify the significant differences between variables such as gender, age and educational level. In order to meet the objectives, we elaborated a corpus of 14 colloquial conversations with 10 hours and 27 minutes of audio recording. The relationships between the interlocutors are friends or family. The identification of the mechanisms used is carried out based on the methodological study of Albelda et al. (2014) 21 types of attenuation mechanism used in the corpus were obtained, the characteristics of the use of the mechanisms showed evidence of the cultural impact on them. Moreover, it revealed that the function of which is the most attenuated, is the function of preventing threats to the interlocutor's face, and the one that is least attenuated is the function of repair the damage caused by the face threating act. In all the types of speech act attenuated we found that in the assertive act there are a greater number of cases by using attenuation mechanism. At last, it has been shown that there are differences in the usage of attenuation mechanism according to gender, age and educational level. / Zhao, L. (2021). Estudio de la atenuación en conversaciones coloquiales chinas [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/164921

Yes / In this technical note, stochastic coupling attenuation is investigated for a class of multi-variable bilinear stochastic systems and a novel output feedback m-block backstepping controller with linear estimator is designed, where gradient descent optimization is used to tune the design parameters of the controller. It has been shown that the trajectories of the closed-loop stochastic systems are bounded in probability sense and the stochastic coupling of the system outputs can be effectively attenuated by the proposed control algorithm. Moreover, the stability of the stochastic systems is analyzed and the effectiveness of the proposed method has been demonstrated using a simulated example.