Texas A&M University-Kingsville: AKM Digital Repository
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1689 research outputs found
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Design and control of multilevel converters for grid-connected renewable energy sources
No full textThe interest in renewable energy is growing very fast all over the world. Along with the distributed generation system, renewable energy sources are now supplying power to the grid. For large-scale renewable energy sources such as wind turbine, solar photovoltaic, etc., integration to the grid requires high power rated converters. In this case, a two-level topology cannot fulfill the demand whereas a multilevel topology can significantly show its potential for high power density. Moreover, multilevel converters produce very low harmonic distortion due to high switching frequency capacity offered by the newly developed SiC and GaN power electronic devices. The multiple-level output waveform creates a smoother sinusoidal signal that requires a very small filter. Consequently, a higher number of switches distribute voltage stress across each switch leading to a reduced power loss.
This research investigated different multilevel topologies for renewable energy source integration to the grid and design a closed-loop controller-based grid-connected multilevel converter. As multilevel converters are very promising for high power density and also adaptable for large-scale renewable energy integration to the grid, it is essential to know how to design and select our devices along with the operating parameters of the converter since this topology consists of multiple switches and devices. One of the important parameters for converter design is the switching frequency which needs proper attention. For instance, low-voltage rated devices offer very high switching capability, but the switching capability for medium or high-voltage rated devices is very limited because of the junction temperature of the device and high energy losses. An in-depth analysis of converter losses and relation to the switching frequency with thermal conditions are performed indicating that almost 70% of the losses occurred during the switching period of the semiconductor devices, directly proportional to the switching frequency. Moreover, a novel modulation technique is also developed to increase the multilevel converter efficiency. The modulation technique is applied and validated in different multilevel converter topologies.
Moreover, the grid connected inverters are at a high risk of cyber security as they provide remote access to the user for real time monitoring and control. This research also investigated the vulnerability of power converters and proposed an IoT-enabled solar microinverter that uses a blockchain technology to improve the security
Meta-synthesis of simulated learning outcomes among speech-language pathology graduate students
No full textThe use of simulated learning has been well established with supportive evidence in health-related disciplines for decades. While the use of this type of learning within the speechlanguage pathology field has grown, the efficacy and outcomes of this practice within the field is just emerging despite the amount of research supporting simulation and simulated learning benefits. To date, there is no known comprehensive understanding or qualitative synthesis of simulated learning practices and associated student learning outcomes within the field of speechlanguage pathology. As such, the purpose of this study explored the perceived student learning experiences, perspectives, and associated outcomes of simulated learning in the discipline of speech-language pathology. This study employed the conceptual framework of Kirkpatrick's model of learning to evaluate the use of simulated learning in the educational practice field. The research question used to guide this study is: what are student learning perceptions, subjective outcomes, and attitudes about simulated learning that shape the overall simulated experience. This study utilized criterion-based, purposeful sampling consisting of empirical studies published in peer-reviewed journals and dissertations. A qualitative meta-synthesis design, specifically a thematic synthesis, was used to synthesize the findings of established primary qualitative and qualitative components of mixed-method research into descriptive and analytical themes through coding and content analysis
Self-supported nano catalysts for electrochemical seawater splitting
No full textThe overarching objective of this research project was to design a cost-effective electrocatalyst viable for producing green H2 by investigating different strategies that are expected to lead to an electrocatalyst with fast kinetics for mass and electronic transfer and sustained a high geometric activity at low input voltage. These strategies include producing electrocatalysts with: (1) Synergistic electronic modulation: The electronic structure of transition metal (TM) based catalyst was tuned by creating oxygen vacancies, heterogeneous doping of heteroatoms (B, S, Cl), strain effect, etc. The protective layers (borate and hydroxide) were introduced next to the OER active sites to block the Cl- adsorption and increase the selectivity and durability of anode material. (2) Surface and structural optimization: The surface of the synthesized nanoclusters (NCs) catalysts was optimized at the nanoscale by controlling the surface coverage of the NCs to increase the aerophobicity of the electrocatalyst. Amorphousness was introduced in the catalyst structure to enhance the electrochemical active surface area (ECSA), hydrophilicity, self-healing, and surface reconstruction characteristics of the material to increase the reactivity and chemical durability of the nanocatalyst. Porosity was created to enhance the diffusion channels for mass transport and gas releasing ability to mitigate the catalyst degradation resulting from the blockage of active sites. (3) Strong catalyst-support interaction: Compared to conventional powder materials, self-supported (free standing) electrode materials were designed through anodization, electrodeposition, hydro/solvothermal, and microwave assisted synthesis strategies to grow active sites on the current collector directly (substrate) to evade post coating process, which decrease the cost and simplifies the electrode fabrication process. The increased interaction of active sites with the substrate enhances the charge transfer rate at the interface and reduces the leaching probability at a high current density where immense gases are produced. These electronic and structural features were successfully fitted into one electrocatalyst that provides a large specific surface area, high electrical conductivity, ionic mobility, intrinsic activity for each active site, and efficient charge transfer, leading to an outstanding catalytic performance. The synthesized catalysts were investigated with advanced characterization tools such as electron microscopy (SEM, TEM, HRTEM, SAED, AFM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) before as well as after electrolysis to probe any variations in morphological, compositional, or physical properties which might affect the reaction kinetics. Based on the electrochemical and physical characterizations we believe that these novel nanostructured materials can be capitalized for the realization of direct seawater electrolysis
Migration, movement, and winter ecology of midcontinent greater White-fronted Geese
No full textAnimal movement strategies are the result of both environmental and physiological effects, and the relationships between these factors is central to understanding the drivers and consequences of movement in animal ecology. The advent of high resolution tracking devices equipped with additional sensors allows unprecedented insights into animal movements, behaviors and decision-making strategies. Greater white-fronted geese (Anser albifrons frontalis) in Midcontinent North America have undergone a large-scale winter distribution shift in recent years, the causes and consequences of which are unknown. How they move across the landscape, move among habitats, and behave within them, may depend on their behavioral plasticity to habitat distribution. These factors, in addition to migration characteristics, may also contribute to spring migration strategies that influence breeding performance. We used global positioning system tracking devices with on-board accelerometers to investigate migration, movement, and winter ecology in Midcontinent Greater White-fronted Geese. In Chapter I, we investigate how individual decision-making in white-fronts is influenced by their behavior, environmental effects, and wintering region, on the outcome of transitioning among habitat types. We found that behavioral time allocation, wintering region, and environmental effects explained variation in the probability of transitioning among habitats, with differing patterns among similar habitat types. In Chapter II, we investigated how white-fronts move among ecologically-distinct wintering regions, and if there were energetic costs to wintering in contemporary regions rather than historical regions. We found that white-fronts frequently moved throughout their geographic range over the course of winter, and exhibited landscape-level knowledge of wintering areas, contrasting previous hypotheses regarding winter philopatry. Additionally, energy expenditure was greater in contemporary wintering regions due to increased time spent foraging and in flight, indicating there may be energetic consequences of distribution shifts. In Chapter III, we examined whether carry-over effects from wintering region and migration characteristics influenced the probability of attempting to breed, and if a breeding attempt was successful or failed. We found a strong longitudinal difference in arrival to the breeding grounds, pre-nesting duration, and nest initiation dates between eastern and western breeding regions, but no migration characteristics or carry-over effects from winter were influential to breeding performance. Therefore, factors that govern breeding performance likely occur primarily upon arrival to breeding areas or are related to individual quality and previous breeding performance. In conclusion, greater white-fronted geese revealed extreme plasticity in wintering and migration characteristics, influenced by the combination of decision-making strategies, landscape configuration and habitat features, and individual heterogeneity
3D seismic characterization and prospect assessment of the upper miocene interval, virgo block, offshore Louisiana, Gulf of Mexico
No full textThe Virgo Block has been proven as one of the highest hydrocarbon potential and low operational risk regions in the Gulf of Mexico (GOM) basin. Despite the northeastern region of the Virgo Block not fitting into the typically recognized exploration plays on the continental shelf, the southwestern region on the upper continental slope is characterized by suitable properties comparable with the generally accepted deeper exploration plays found in the GOM basin.
In this study, the main structural setting in the Virgo Block, offshore Louisiana, was interpreted using 262 km2 of 3D seismic data, biostratigraphic tops, and well log data. The main seismic reflectors, the tops of Cretaceous and Miocene, were picked across the interest area for assessing the main structure. The dominant structural features in the interest area comprise growth faults and accompanying synthetic and antithetic faults, and salt diapirs. These faults fractured mostly the middle and upper section of the Miocene while the salt diapirs served as migration pathways between the Cretaceous and the Miocene.
Two seismic amplitude anomalies associated with middle and upper Miocene sandstones were assessed. These amplitudes may represent direct hydrocarbon indicators linked to gas saturated sandstones. The type of traps interpreted includes three-way dip closure against multiple faults, and four-way dip structural closure associated with deepwater fan systems (turbiditic fan lobes) deposited on a regional slope and base-of-slope environments. The two top-ranked prospects represent fan lobes partially overlapped and could contain ~111 billion cubic feet of gas. The chance of geologic success for these two prospects is about 66% and 52%, respectively
A homemaking program for Spanish culture girls of Kleberg county: planned in accordance with findings from a study of their home life
No full textIt is the purpose of this research, (1) to study the need of this Spanish culture homes in Kleberg County, Texas, particularly such needs as might be met with education of their girls in homemaking at the fourth, fifth and sixth grade levels of the public schools attended by those girls, and (2) to plan a program in homemaking for them that can be carried on in those schools. To do this, involves a study of (1) conditions in the home, (2) the Spanish culture home towards citizenship and education
Distinctive qualities of the poetry of Robert Frost
No full textAdmirers of Robert Frost--and these, if we may judge by the many recent scholarly studies that have been made of his poetical works are rapidly increasing in number as well as in appreciation--are all agreed on one point, namely, the author's uniquely ability to interpret his own rural New England. There are, however, other phases of this poets work which afford interesting problems for discussion and critical analysis. Thus, it is the purpose of the writer of this thesis, after having made a careful study of all the available poems of Robert Frost, to present certain distinctive qualities of his work, heretofore largely overlooked or at least but casually considered. His range of expression, patterns of sensitivity, style and spirit, will be treated separately in the order here mentioned. In the belief that a brief critical study of the author's biography will serve to elucidate the personal and circumstantial characteristics of his poetry, the reader is afforded a preliminary chapter dealing with the significant facts of Frost's life
The organization and growth of vocational education under the national vocational education acts
No full textThe problem of this thesis is stated as follows: 1. To show the organization and growth of vocational education under the National Vocational Education Acts with regard to appropriations, enrollment, and teachers. 2. To prepare a complete study in vocational education dealing with Agricultural Education, Homemaking Education, Trade and Industrial Education, with aims to knowledge as a basis for making vocational education attractive
An analysis of the political novel on national politics, 1865-1900
No full textToday as never before, a video interest in politics holds the American people. Whether it be national or international, the problem of politics becomes more important to the individual. There is some allusion to the problem in some form of the other in more and more of our fiction. Many of our novels today may be classified as political novels, and the trend to include political motivations is increasing
Early transportation in the Brownsville, Texas area
No full textThe crooked Rio Grande, international boundary between the United States and Mexico, presents certain problems of vital concern in the fields of transportation, economics, and the everyday struggle of the people who live along its banks. To the adventurous pioneers of yesterday, a roving population of Spanish, French, German and Italian extraction, it presented the physical problems of transportation, water barrier, and occasional floods. As time passed the economic life of these pioneers became more complex. It enlarged and intermeshed with the outside world, and as it did so the importance of the transportation both cross up and down the river increased. Pioneer methods of river transportation were colorful, and this activity has not lost it color through the years. It is still a delightful phase of life along the lower Rio Grande