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Robust Velocity Dealiasing for Weather Radar Based on Convolutional Neural Networks
Get PDFDoppler weather radar is an essential tool for monitoring and warning of hazardous weather phenomena. In weather radar, achieving a longer aliasing range (ra) is crucial for surveillance, and a higher aliasing velocity (va) is also important to obtain dynamical information of storms unambiguously. However, the desire for longer ra and higher va creates a conflict because these two parameters are inversely related to the pulse repetition time (PRT). This conflict is known as the "Doppler dilemma", as ra and va cannot be improved simultaneously using a single PRT. This phenomenon is more challenging at shorter wavelengths, which means it has a more significant impact on X-band, followed by C-band and S-band. There are two main approaches to mitigating this issue. The first approach to dealias the velocity is the post-processing method. This method checks for abrupt changes from one end of the va to another, and a fold is detected when such instances are encountered. The underlying assumption is that the velocity field should be spatially continuous. This approach performs well for wide and spatially continuous storms. However, it still suffers when the storms are isolated within the radar field of view. The second approach is the waveform design method, which utilizes two or more pulse repetition times (PRTs), and the aliased velocities are found by searching for disagreement between two or more velocities observed from different PRTs. Velocity dealiasing is performed by solving a least-common-multiple problem. However, this method still has the inherent limitation of ra. The post-processing method allows the system to operate everything else, such as ground clutter filter, continuous pulse-pair processing, etc., as waveform design methods require modifications to the existing filters. Therefore, in this study, the main focus will be on the post-processing method, and the key is to detect the aliased velocity accurately, leading to the correct velocity dealiasing. The detection of aliased velocity can be compared to classification. Raw aliased velocity can be regarded as the input image, and the aliased count can be regarded as label. With advancements in technology, machine learning can be applied to image classification. Convolutional neural networks (CNNs) are widely used for image segmentation, enabling the model to output the same size as the input image. Therefore, in this study, a CNN is utilized to tackle the velocity dealiasing issue. In the training process, the input data comprises aliased velocity and the aliased count (the sign and how many times they are aliased). The best weights and the biases are determined through a fit-and-adjust process. After the training process, the performance is evaluated using unseen test data. The aliased velocity is used as input, and the output is the aliasing count. Velocity dealiasing is performed by combining the input (aliased) velocity, the aliasing count, and the known va. For evaluation, the CNN method is compared to the traditional region-based method, which is also a post-processing method in Python ARM Radar Toolkit (Py-ART). Both methods are evaluated on mostly filled precipitation and sparsely filled precipitation. Sensitivity tests are conducted on template size and the va used to optimize the CNN model to cover the X-band range coverage. This model can be used regardless of va. Both methods demonstrate similar performance on mostly filled precipitation. However, the CNN method shows better performance on sparsely filled precipitation, as it processes the entire scan at once while the region-based method only processes the limited adjacent area. The overarching goal of this study is to exploit CNN for velocity dealiasing and to achieve human-level performance. Through this process, it is expected that the labor-intensive work could be automated
Flame Synthesis of Tungsten/Molybdenum Oxide Nanoscale Heterostructures with Complex Physical Morphologies
Get PDFThe focus of this dissertation is to investigate the synthesis of crystalline transition metal oxide (TMO) structures in a counter-flow diffusion flame. This thesis examines the underlying mechanisms for the flame synthesis of 1D, 2D and 3D nano and micron scaled TMO structures on the solid support and in the flame gas-phase. The understanding of the growth mechanisms of the synthesis of single metal structures, along with hybrid and heterostructures with complex morphologies is essential to tailor the fabrication of TMO nanoscale structures. These new novel structures enable a multiplicity of applications in critical areas of todayโs world economics such as clean energy and sustainability (i.e. solar energy, batteries, smart buildings, gas sensors, etc.). The source material, solid supports of high purity transition metals, in the form of wires are introduced in the flame medium to trigger the synthesis of crystalline nanostructures. The insertion of single and dual solid supports in the oxygen-enriched diffusion flame is investigated along with the rapid formation of structures in the gas-phase. The solid support serves as, both, the material source and the site for disposition, allowing for crystallization of the formed structures at different locations around the surface of the metal probes. The study presented herein commenced with the fabrication of 1D and 3D tungsten-oxide nanostructures on the surface of a single solid support (i.e., W probe) inserted in the opposed-flow oxy-fuel flame. The unique 1D nature of the counter-flow diffusion flame, along with is high thermal and chemical species gradients favors the transformation of bulk transition metals into 1D, 2D, and 3D structures with complex morphologies. The physico-chemical properties of the transition metal probe (i.e., diameter and elemental composition) and flame composition (i.e., oxygen content in the oxidizer stream) were varied to investigate their influence on the synthesized nanostructures. We hypothesize that the concentration rate of metal oxide vapors generated from the surface of the probe, once inserted in the oxygen-rich flame medium, along with flame residence time, flame oxidizer composition and precursor location in the flame volume are key parameter for controlling the morphology of the structures. All of the mentioned factors can influence flame temperature and composition of oxygen species, along with the rates of oxide generation, subsequent crystallization and morphologies of the structures formed. Moreover, the unique structure of the 1D flame geometry with one region rich in carbon species and the other in oxygen radicals can be leveraged for the synthesis of even more complex assemblies such as hybrid carbon-metal oxide structures.
The formation of triangular, rectangular, square, and cylindrical 3D channels with completely hollow or semi-hollow morphologies was achieved by varying the probe diameter from 1.0 to 0.5 mm. Whereas the increase of the O2 content to 100% and the employment of a 1 mm high purity W probe resulted in the growth of 2D ribbon-like micron-sized structures. The lattice spacing of ~0.38 nm measured for the 1D tungsten-oxides closely matches that of monoclinic WO3 structure. X-ray photoelectron spectroscopy analysis revealed that the larger 3D structures also consist of WO3, confirming that the chemical composition of the structures remains the same while tailoring both the probe and flame parameters. The flame geometry was used to synthesize hybrid C-metal oxide structures. This was achieved by inserting a high purity 1 mm diameter W probe into the oxygen rich flame environment (formed with an oxidizer composition of 50% O2 + 50% N2) to form 1D tungsten-oxide structures. The newly formed structures were exposed to the carbon rich environment of the flame, using a sleeve, to coat their surfaces with various layers of carbon shells, thus, forming 1D hybrid nanowires composed of tungsten-oxide cores covered with a uniform carbon sheath. The physical features of the grown structures on the solid support present lengths up to 50 ยตm and diameters ranging from 20 to 50 nm. This study reveals the existence of a common generic mechanism consisting of tungsten-oxides/hydroxides layers being formed on the probe surface (fuel side) exposed to the high-temperature oxidative environment. These oxides/hydroxides layers are then evaporated/sublimated as the metal probe continues being exposed to the flame volume. The formed oxide vapors are then transported by the gas flow towards the stagnation plane and crystalizes in the form of 1D nanomaterials on the upper surface of the probe where the temperatures are lower. The proposed growth mechanism for the 3D structures consists of coalescing of 1D tungsten-oxide nanorods. The growth of the 3D channel hollowed structures is favored by material deposition from the gas-phase along the edges of early formed large cubical structures (Berg effect). Thereby, resulting in deposits of hollowed structures since solely a limited amount of materials can diffuse to the heart of the formed 3D structure. Regarding the hybrid nanowires, a two-step synthesis mechanism is proposed: (i) tungsten-oxide nanorods are formed in the oxygen-rich flame region; (ii) the rapid formation of carbon shells from hydrocarbon species attained from the carbon-rich zone of the flame during the probe removal process.
The gas-phase structure/particle synthesis sets the foundation for increase production of tungsten-oxide nanostructures. The synthesis of well-defined faceted octagonal prisms (octahedron nanoplatelets) and elongated structures of high aspect ratio in the form of rod-like nanocrystals is performed in the flame gas-phase employing a solid-fed precursor flame technique using a 99.9% purity 1 mm diameter W probe as the precursor source. The growth mechanism of the formed nanoscale structures involves the oxidation of the surface of the metallic probe, evaporation of the newly formed oxide layer followed by transport of the metal oxide vapors toward the hydrocarbon-rich zone of the flame. As the transport takes place, the metal oxide vapors are crystallized into well-defined octahedron nanoplatelets and elongated rod-like nanocrystals. The lattice d-spacing of grown nanoplatelets and of the rod-like nanocrystals was measured to be ~0.38 nm closely corresponding to the (002) plane of monoclinic WO3 structures.
The last part of this research consisted of studying the impact of dual solid support synthesis to aid the formation of hybrid and complex structures with a multiplicity of morphologies. W and Mo probes of 1 mm in diameter are inserted in an oxygen-rich zone at flame positions of Z = 13 and Z = 11 mm, respectively. Experiments consisted of simultaneous and varied probe insertion in the flame medium. Evidently, controlling flame position (temperature/radicalsโ concentration), residence time (rate of oxide vapors production), and probe insertion sequence results in the formation of highly complex structures with multiple morphologies (e.g., polyhedral-, tree-, flower-, forest-, and grass-like nanostructures). The growth of these unique structures is driven by the formation of 1D โbackboneโ structures that serves as precursors for the synthesis of the multiple structures with complex morphologies. HR-TEM/EDX/SAED analyses were used to characterize the formed structures. A proposed growth mechanism for the synthesis of these hybrid complex structures is also presented. It is interesting to note that tungsten-oxide structures with unique morphologies were grown not only on the solid support surface but also in the flame gas-phase providing insightful knowledge regarding the mass production of these materials with a wider range of applications
Purpose Driven Partnerships: The Nexus of Purpose and Strategic Alliances
No full textThis dissertation utilizes an abductive mixed methods study to assess, unpack, and extend the theory of purpose. Although prior literature primarily focuses on the outcomes of high purpose framing, this study specifically addresses how one high-purpose, exemplar firm engaged in strategic alliances as a means for formalizing and realizing its purpose. Concomitantly, although the strategic alliance literature typically focuses on the economic and competitive advantages of strategic alliances, this study further introduces the concept of the purpose driven partnership (PDP) to incorporate the more relational and social dimensions of purpose within strategic alliances. Data was collected via 22 interviews with senior executives of the high-purpose firm in combination with 1,266 post-engagement surveys completed over a 5-year period by senior executives from 622 firms in 25 countries and 28 industries. Supplemental data included engagement financials and engagement duration. The results of this study revealed three PDP typesโSustain & Support, Analysis & Strategy, and Change & Transformationโas unique pathways for the firm to formalize its purpose. Next, qualitative analysis of the survey data revealed the presence of six consumer tensionsโsolution clarity, strategic focus, knowledge contribution, resource embeddedness, interpersonal style, and functional autonomyโthat affected how value was assessed by client firms. These value assessments resulted in a subsequent decision of whether to continue the partnership and to consume the value created by the firmโan ongoing process termed as value consumption. As a result of value consumption, consumers described both positive and negative externalities referred to as value gain and value loss. Additionally, the net difference of these outcomes, referred to as net value gain, became predictive of whether client firms would continue to engage with the firm in the future, thereby increasing the firmโs long-term value appropriation. Finally, this dissertation provides important theoretical contributions to the literatures on purpose, strategic alliances, demand-side value creation, and entrepreneurship as well as a foundation for future research
Electron concentration-dependent optical properties of indium arsenide
Get PDFSince humans began using mirrors to reflect light, its control has been a subject of research for thousands of years. With the use of Maxwellโs equations, we came to realize that controlling light is primarily achieved through the manipulation of the refractive index of the material.
Both the real and imaginary parts of the refractive index represent the important optical properties of a semiconductor material. In semiconductors, especially narrow bandgap materials such as InAs, their refractive indices can be significantly modified through manipulation of the materialโs electron concentration. This has been explored in the development of mid-infrared semiconductor lasers such as quantum and interband cascade lasers (ICLs), which are gaining more and more attention for many applications. Hence, it is important to appropriately evaluate the electron concentration-dependent refractive index in semiconductor materials, which depends on the band structure of the material, for the various semiconductors utilized in such structures.
Previously, many researchers used a simplified two-band K ยท P method to calculate the refractive index of semiconductor materials. However, the results obtained from this two-band model were not systematically compared with other competing models. In this thesis, both a three-band model that includes the spin- orbit split-off band, and the two-band model are used to evaluate the refractive index and compared with experimental results to assess their suitability for three scenarios including plasmon waveguide for ICL, high contrast distributed Bragg reflector(DBR) and reflection measurement.
The results provide a guideline for selecting the appropriate model over different wavelength and carrier concentration ranges for various applications. For a carrier concentration ranging from 10^18cmโ3 to 3 ร 10^19cmโ3, the three-band model is more accurate. For carrier concentration larger than 3 ร 10^19cmโ3, the two-band model is more accurate. The experimental data also shows some limitations for K ยท P method. The attained results may contribute to the optimization of ICL performance and help other applications like meta-material, resulting in improved device performance and more accurate measurements
Does EDHF-blockade by fluconazole alter cerebral autoregulation and hemodynamics during lower-body negative pressure?
Get PDFAnimal models suggest that cytochrome P450 2C9 (CYP450), an enzyme within the EDHF pathway, plays a critical role in the control of cerebral hemodynamics and autoregulation. However, this observation has not been directly examined in humans. PURPOSE: To determine the contribution of EDHF to cerebrovascular hemodynamics in healthy young individuals at rest and during mild simulated hypovolemia via blockade of cytochrome P450. METHODS: 16 subjects (9 females, tested only during early follicular phase) participated in 1 familiarization and 2 experimental visits. In experimental visits, participants ingested either a CYP450 inhibitor, fluconazole (FLZ 150mg) or a microcrystalline cellulose placebo (PLA 250mg) in randomized, single-blind, crossover design. Following 120 minutes of supine rest after ingestion middle cerebral artery velocity (MCAv, cm/s, Transcranial Doppler), mean arterial pressure (MAP, mmHg, finger photoplethysmography), prefrontal cortex oxygenation (TSI, %, Near-Infrared Spectroscopy) were continuously measured during 5 minutes of supine rest and 5 minutes of lower-body negative pressure (LBNP, -20mmHg). Cerebrovascular conductance index was calculated (CVCi = MCAv/MAP, cm/s/mmHg). Further, gain, coherence, and phase were determined using transfer function analysis of MCAv and MAP data. RESULTS: Resting values for all variables were not different between treatments (p > 0.05). Therefore, all data are presented as a change () from rest to LBNP ยฑ SD. MCAv decreased from rest to LBNP with FLZ (p = 0.001) but did not differ between treatments (PLA -3.11 ยฑ 7.04 vs. FLZ -6.61 ยฑ 6.00 cm/s, p = 0.17, d = 0.36). Similarly, CVCi decreased between rest and LBNP for FLZ (p = 0.02), but did not differ between treatments (PLA -0.04 ยฑ 0.09 vs. FLZ -0.06 ยฑ 0.06 cm/s/mmHg, p = 0.19, d = 0.35). FLZ responses to LBNP were significantly different than zero for both CVCi and MCAv measures (ฮMCAv -6.61 ยฑ 6.00, p = < 0.001, r = 0.622; ฮCVCi -0.06 ยฑ 0.06, p = 0.001, r = 0.549). TSI was unaltered from rest to LBNP, nor by treatment (PLA 0.03ยฑ1.45 vs. FLZ -0.02ยฑ1.25 %, p = 0.41, d = 0.213). Transfer function analysis was performed but not interpreted, as coherence values were not consistently above 0.5, which is not an unanticipated result when analysis is applied to healthy young adults. CONCLUSION: This study indicates that cytochrome P450 inhibition does not affect middle cerebral artery velocity, CVCi, or prefrontal cortex oxygenation at steady-state rest or during mild-hypovolemic stress. However, EDHF-blockade does appear to alter hemodynamic responses to sympathetic stress. Therefore, these data suggest that CYP450 is not compulsory for regulation of cerebrovascular hemodynamics in healthy young adults, however, may be critical for dynamic cerebral responses to drops in blood pressure
Prima Donna Culture and the Tulsa Opera, 1954--1968
Get PDFThis thesis explores the role of prima donnas in the Tulsa Opera in the mid-20th century and how women both onstage and offstage were essential to the development of the Tulsa Opera Company and American opera at large. I rely on the framework of Lawrence W. Levine to examine the development of cultural hierarchies in America in conjunction with the establishment of opera in America. An examination into the origins of opera in Tulsa demonstrates how important that elite women and women in managerial roles were to the creation and evolution of the organization. They were key to securing funds and establishing a business model which allowed them to import outside talent, specifically prima donnas from the Metropolitan Opera. The prima donnas were key to elevating the performance quality of the Tulsa Opera, demonstrating the integral role of women in early American opera. This is especially notable when reflecting on 19th-century stigmatization of prima donnas resulting in sexualization and lack of respect for the profession as it diverted from the feminine ideal of remaining in the domestic sphere. An examination of the representation of Tulsaโs visiting prima donnas in the 20th-century popular press shows how this earlier stigma has been transformed in many respects, ultimately leading to prima donnas being highly respected for their craft both in Tulsa and throughout the country
Creditorsโ Rights and Management Forecast Decisions: Evidence from a Quasi-Natural Experiment
No full textI study how creditorsโ rights affect managementโs disclosure decisions, employing the introduction of anti-recharacterization laws in the United States as an exogenous shock to creditorsโ rights. These laws increased the rights of creditors by enhancing their ability to repossess collateral pledged for secured lending. I find that after the enactment of the laws, managers were more likely to issue a forecast and the number of forecasts increased. However, there is no evidence to suggest that management sacrifices forecast quality in the process. Further tests reveal that the response is stronger for companies with higher levels of shareholder monitoring, implying an indirect effect of creditorsโ rights as a governance mechanism
The design of an experimental testing fixture to test seals of various geometries exposed to extreme operational conditions while operating in dynamic rectilinear motion
Get PDFRadial reciprocating seals are available in a multitude of materials and physical configurations. The most used seal configuration is a circular cross section polymer ring shaped seal, O-ring seal. While affordable and small in cost, seals are essential to the functionality of many mechanical direct to consumer purchased products and industrial implements. Seal design and material selection is essential to the performance and functionality of the seal. With the multitude of different seal configurations, quantifying seal performance characteristics remains difficult. Efforts taken by the manufacturer to publish technical data of seals often only tailors to a very specific application. Being that a seals performance relies highly on parameters such as pressure, compression, lubrication, and application specifics such as remaining static or sealing dynamically, some means of classifying sealing behavior needs development.
In this thesis an outline of the eight-phase morphology of design process will be employed to develop a means of identifying inefficiencies and achievements of varying seal architectures used for seals in components of dynamic rectilinear motion. With this design process an experimental testing fixture will be designed and commissioned. This fixture serves as a device to answer research questions revolving around the testing of seals experiencing the exposure to assorted operational environments. Performance data of interest will be recorded in real time and then analyzed to give a statistical identifier of seal efficiencies or inefficiencies
Assessment of spectral attributes in identifying gas hydrates in seismic data from the Pegasus Basin, offshore New Zealand
Get PDFGas hydrates are formed in the subsurface along shallow ocean basins or in permafrost settings, and are commonly identified in the seismic data by the bottom-simulating reflector (BSR). Various methods have been employed in the past to measure gas hydrates from lab analyses, well log, or velocity data, but few studies have demonstrated methods to identify gas hydrates in seismic data when the BSR is sparse or lacking. One approach is to measure the expected attenuation, or the reduction in the seismic waveform, caused by hydrates in the gas hydrate stability zone (GHSZ). This study proposes the application of two statistical attributesโskewness and kurtosisโthat measure the asymmetry of the seismic amplitude spectrum in order to quantify the attenuation responses throughout the GHSZ. Although the study area does not contain well log data, there are numerous studies that confirm hydrates exist throughout the Pegasus Basin. These attributes, in addition to other instantaneous and amplitude-related attributes, demonstrate that frequency-related variations are the major contributors to attenuation response, rather than seismic amplitude or geology effects. The spectral attribute results show that strong positive skewness and kurtosis variations above the high amplitude BSR is likely due to attenuation through an interval of hydrates. Negative skewness and kurtosis may correspond to an interval that does not contain hydrates, therefore suggesting that the GHSZ in the Pegasus Basin consists of discontinuous intervals of hydrates, rather than one continuous layer from ocean bottom to BSR
Interpretation of shear wave velocity in unsaturated soils
Get PDFShear wave velocity measurements in soil can provide estimates of small strain stiffness and are used for seismic site classification. In comparison to saturated soils, there has been relatively little research on the behavior of shear wave velocity in unsaturated soils. Current research was conducted to understand the behavior of shear wave velocity in unsaturated soil. The objectives of this research were to: 1) Investigate the effect of various soil properties on the behavior of shear wave velocity in unsaturated soils. This included studying the effect of soil type, moisture content, suction, confining stress, wetting-drying hysteresis, density, and soil structure. 2) Compare and analyze shear wave velocity measurements taken in the field and the laboratory. 3) Investigate the effect of seasonal changes in moisture content on shear wave velocity measurements from the Seismic Cone Penetrometer (SCPT), and the potential impact on seismic soil properties and site classification. And finally, 4) develop a model that uses the physical and mechanical properties of the soil to estimate the shear wave velocity for different soil types under various saturation conditions.
To achieve the objectives of this study the following tasks were completed: 1) Performed shear wave velocity laboratory testing on soil samples undergoing the vapor equilibrium suction control for wetting and drying paths using the bender elements method with and without confining stress. 2) Performed SCPTu shear wave velocity measurements at twelve sites and recorded seismic velocity measurements at 1 m depth intervals. 3) Performed shear wave velocity testing in the laboratory on soil samples from the field under stress conditions similar to the field. 4) Investigated proposed relationships in the literature and based on them, develop a new model for predicting shear wave velocity that includes the desired properties and stress conditions of the soils.
The major contributions of this research include: 1) Shear wave velocity was tested under various conditions where soil type, water content, suction, density, confining stress, and soil structure were varied and the combined effect of changing these parameters was assessed. 2) An investigation of shear wave velocity with the seismic cone penetrometer in the field at nine test sites during wet and dry seasons demonstrates the importance of considering changes in shear wave velocity due to changes in moisture content and suction in the active zone of the soil profile. This has important implications for the determination of soil dynamic properties and seismic site class based on field measurements of shear wave velocity in unsaturated soils. 3) A systematic comparison of shear wave velocity determined using SCPT in the field and bender element testing in the laboratory on Shelby tube samples obtained on the same day was accomplished for three different test sites. The study revealed that field measurements were nearly the same as lab measurements made under similar confining stress. These results indicate that measurements of shear wave velocity, whether in the field or lab, are robust and reliable. 4) Existing power models for predicting shear wave velocity with effective stress were examined and a new linear model was developed and found to provide better predictive capability than the power model