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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
181

Efficient FE Modeling of Large Casted Parts / Effektiv FE modellering av stora gjutna detaljer

Amirapu, Lalitha Swetha, Yalamanchili, Haswanth January 2023 (has links)
The design and analysis of large casted parts present significant challenges due to their complex geometry. Finite Element (FE) modeling is a vital tool for understanding the performance of casted components. However, the computational requirements associated with these parts often lead to excessive processing times and resource utilization. This thesis aims to enhance the efficiency of the mid-surface model creation by developing an FE modeling approach suited explicitly for large casted components. The study begins by exploring the background of casted parts and their applications. A comprehensive analysis of modeling and meshing techniques is conducted, emphasizing their application to large casted components. Building upon this knowledge, different ideas are examined, leading to the proposal of a methodology combining CAD strategies for design features, hybrid meshing techniques, and approaches aimed at reducing FE modeling time to streamline the overall process.To validate the proposed approach, a series of case studies involving casted parts with varying levels of complexity are undertaken. Real-world casting process parameters are considered, highlighting the advantages and limitations in each ideation phase. The proposed methodology is tested and show cased to expert engineers to evaluate its efficiency and feasibility. Furthermore, the efficiency of the new approach is quantitatively evaluated in terms of processing time. The developed methodology offers engineers and researchers a powerful tool to accelerate the design process and optimize FE modeling time while managing computational costs. As industries continue to push the boundaries of size and complexity in casted part design, the insights and techniques presented in this thesis offer a valuable resource for addressing the various engineering challenges inherent in future endeavors. / Utformningen och analysen av stora gjutna delar innebär betydande utmaningar på grund av deras komplexa geometri. Finita Element (FE)-modellering är ett viktigt verktyg för att förstå prestandan hos gjutna komponenter. De beräkningskrav som är förknippade med dessa delar leder dock ofta till alltför långa handläggningstider och resursutnyttjande. Detta examensarbete syftar till att förbättra effektiviteten av skapandet av mittyteta modeller genom att utveckla en FE-modelleringsmetod som är specifikt lämpad för stora gjutna komponenter. Studien börjar med att utforska bakgrunden till gjutna delar och deras tillämpningar. En omfattande analys av modellerings-och diskret iseringstekniker genomförs, med tonvikt på deras tillämpning på stora gjutna komponenter. Med utgångspunkt i denna kunskap undersöks olika idéer, vilket leder till förslaget om en metod som kombinerar CAD-strategier för designfunktioner, hybridmodelleringstekniker och tillvägagångssätt som syftar till att minska FE-modelleringstiden för att effektivisera den övergripande processen. För att validera det föreslagna tillvägagångssättet genomförs en serie fallstudier som involverar gjutna delar med varierande nivåer av komplexitet. Verkliga gjutprocessparametrar beaktas, vilket belyser fördelarna och begränsningarna i varje idéfas. Den föreslagna metoden testas och visas upp för expertingenjörer för att utvärdera dess effektivitet och genomförbarhet. Dessutom utvärderas effektiviteten av det nya tillvägagångssättet kvantitativt i termer av handläggningstid. Den utvecklade metoden erbjuder ingenjörer och forskare ett kraftfullt verktyg för att påskynda designprocessen och optimera FE-modelleringstiden samtidigt som de hanterar beräkningskostnader. När industrier fortsätter att tänja på gränserna för storlek och komplexitet idesign av gjutna delar, erbjuder de insikter och tekniker som presenteras i denna avhandling en värdefull resurs för att ta itu med de olika tekniska utmaningarna som är inneboende i framtida strävanden.
182

Effects of Imazapyr and prescribed fire on vegetation and bird communities in mid-rotation CRP pine plantations of Mississippi

Singleton, Lindsey Rae Carpenter 03 May 2008 (has links)
Appropriate management of mid-rotation pine plantations can improve habitat for early successional and pine-grassland adapted avian species. I tested effects of Imazapyr selective herbicide and prescribed fire on plant and avian communities in thinned, mid-rotation pine stands contracted under the Conservation Reserve Program. Within 12 replicate sites, 2 8.1-ha plots were assigned either herbicide and prescribed fire treatment or control. I described components of vegetation structure and composition in 2006. I tested effects of herbicide and prescribed fire treatment on avian relative abundance, species richness, total avian conservation value, and density of select species during 2003 - 2006. Hardwood midstory decreased and abundances of grasses and forbs increased following treatment. A shift occurred in the bird community from closed-canopy forest species to early successional and pine-grassland species. Treatment stands benefited many avian species exhibiting negative population trends.
183

DO FEATURE IMPORTANCE AND FEATURE CENTRALITY DIFFERENTIALLY INFLUENCE SEMANTIC KNOWLEDGE IN INDIVIDUALS WITH APHASIA?

Cox, Violet O. 30 November 2009 (has links)
No description available.
184

Characterization of the mid-infrared wavelength dependent loss in hollow core photonic crystal fibers

Harner, Mary January 1900 (has links)
Master of Science / Department of Physics / Brian Washburn / This research sought to characterize the length dependent loss of hollow core photonic crystal fibers (HC-PCF) in the mid-infrared. These fibers are used in gas-filled fiber lasers that operate in the mid-infrared range. A black body source which provided a broad mid-infrared spectrum was coupled into a HC-PCF and a fiber cut-back method was implemented to make the length dependent loss measurement. A monochromator was used to observe narrow bands of the broad spectrum provided by the black body source and the loss as a function of wavelength was constructed. The loss for four unique HC-PCF fibers was characterized across the wavelength range [lambda] =1754 nm to [lambda] =3220 nm. The best fibers demonstrated a loss of less than 2 dB/m across this range, with some fibers even exhibiting loss below 1 dB/m.
185

The role of gut microbes on the efficacy of Bt maize against lepidopteran stem borers / Megan van Staden

Van Staden, Megan January 2015 (has links)
The evolution of pest resistance to Cry proteins threatens the long-term use of Bt crops. Busseola fusca developed resistance to Bt maize in South Africa but the mechanism of resistance is not well understood. According to the gut microbiota theory, extensive cell lysis caused by Cry proteins provide gut microbes access to the more favourable environment of the hemocoel where they germinate and reproduce, causing septicemia and death of the host. This theory brought on questions about the role of gut microbes in the efficacy of Bt maize against target lepidopteran pests. The aim of this study was to determine whether microbes present in the mid-gut of B. fusca influence the efficacy of Cry 1Ab proteins. Larvae were collected from 30 different geographical locations, dissected to excise the midgut and mid-gut content which was separated according to morphological types. The morphological types were used to test the antibiotic susceptibility of the bacteria and proved that ciprofloxacin, ampicillin and doxycycline were the most effective bacteriostatic and bactericidal antibiotics. These three antibiotics were exposed to the morphological types at different concentrations to visualise the possible deleterious effects of the antibiotics on the bacteria. This visualisation was performed by observing the growth curve of the bacteria in the presence of the combination of antibiotics. The antibiotics concentration of 500 μg/ml showed the highest efficacy compared to the other concentrations tested. An antibiotic concentration of 500 μg/ml of ciprofloxacin, ampicillin and doxycycline was incorporated into an artificial diet for the larvae to feed on for 7 days. This method was used to rid the larvae of gut microbes before allowing them to feed on Bt maize (MON810) plant material expressing Cry proteins. The results suggests that by placing antibiotic reared larvae on a Bt plant, the absence of the mid-gut microbes contributed to larvae survival on Bt maize. This observation will contribute to understanding the role of gut microbes on the efficacy of Cry proteins. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015
186

The role of gut microbes on the efficacy of Bt maize against lepidopteran stem borers / Megan van Staden

Van Staden, Megan January 2015 (has links)
The evolution of pest resistance to Cry proteins threatens the long-term use of Bt crops. Busseola fusca developed resistance to Bt maize in South Africa but the mechanism of resistance is not well understood. According to the gut microbiota theory, extensive cell lysis caused by Cry proteins provide gut microbes access to the more favourable environment of the hemocoel where they germinate and reproduce, causing septicemia and death of the host. This theory brought on questions about the role of gut microbes in the efficacy of Bt maize against target lepidopteran pests. The aim of this study was to determine whether microbes present in the mid-gut of B. fusca influence the efficacy of Cry 1Ab proteins. Larvae were collected from 30 different geographical locations, dissected to excise the midgut and mid-gut content which was separated according to morphological types. The morphological types were used to test the antibiotic susceptibility of the bacteria and proved that ciprofloxacin, ampicillin and doxycycline were the most effective bacteriostatic and bactericidal antibiotics. These three antibiotics were exposed to the morphological types at different concentrations to visualise the possible deleterious effects of the antibiotics on the bacteria. This visualisation was performed by observing the growth curve of the bacteria in the presence of the combination of antibiotics. The antibiotics concentration of 500 μg/ml showed the highest efficacy compared to the other concentrations tested. An antibiotic concentration of 500 μg/ml of ciprofloxacin, ampicillin and doxycycline was incorporated into an artificial diet for the larvae to feed on for 7 days. This method was used to rid the larvae of gut microbes before allowing them to feed on Bt maize (MON810) plant material expressing Cry proteins. The results suggests that by placing antibiotic reared larvae on a Bt plant, the absence of the mid-gut microbes contributed to larvae survival on Bt maize. This observation will contribute to understanding the role of gut microbes on the efficacy of Cry proteins. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015
187

Effectiveness of a Pedestrian Hybrid Beacon at mid-block pedestrian crossings in decreasing unnecessary delay to drivers and a comparison to other systems

Godavarthy, Ranjit Prasad January 1900 (has links)
Master of Science / Department of Civil Engineering / Eugene R. Russell / Pedestrian signals, particularly at signalized, mid-block crossing can cause delay to drivers after pedestrians’ have successfully crossed, which is termed “unnecessary delay” in this study. In many cases at a mid-block signal, a pedestrian pushes the button and then quickly crosses the street as soon as the walk signal appears and drivers still face several seconds of solid red ball and by law must remain stopped. On a busy street, a queue of vehicles waiting after all pedestrians have crossed can amount to hundreds of hours of unnecessary delay per year. The ‘Pedestrian Hybrid Beacon’ (Initially named a HAWK (High Intensity Activated Crosswalk)) Beacon was proven to be effective in decreasing this unnecessary delay when compared to standard signalized mid-blocks. The City of Lawrence, Kansas was interested in experimenting (as a HAWK beacon was considered experimental when they were installed) with a pedestrian hybrid beacon and they installed their first pedestrian hybrid beacon at a mid-block crossing on 11th street and a second pedestrian hybrid beacon at mid-block crossing on New Hampshire street, Lawrence, Kansas, which were the sites of interest for this research. A study was conducted at these sites to determine the effectiveness of the pedestrian hybrid beacon in decreasing the unnecessary delay to drivers by comparing it to a signalized mid-block crossing on Massachusetts Ave in Lawrence, Kansas. Apart from the delay measurements for these two sites, other parameters such as driver compliance rate to the signal, pedestrian compliance rate, and other driver and pedestrian characteristics were also studied. Video cameras were used to capture video at these sites and the effectiveness of the pedestrian hybrid beacon was analyzed from the video. The HAWK, now in the MUTCD as a Pedestrian Hybrid Beacon, proved to be effective in decreasing the unnecessary delay for drivers in this study. The City of Lawrence had a total of six pedestrian hybrid beacons in operation as per the information received in March 2010.
188

Development and application of spectroscopic techniques in the mid-infrared

Whittaker, Kimberley Elaine January 2014 (has links)
Applications of laser absorption spectroscopy for trace gas detection are many and diverse, ranging from the environmental and atmospheric to the medical and industrial. The aim of creating a spectrometer which combines high sensitivities and selectivities (in order to measure small amounts of absorbers or species that are only weakly absorbing, in a complex background matrix) with a wide spectral coverage (to allow broadband absorbers or multi-component samples to be studied) can be realised by implementing three separate concepts: the exploitation of the strong, fundamental transitions of the mid-infrared; the use of sensitive spectroscopic techniques; and the selection of a widely tunable laser source. In this thesis, these ideas are investigated individually and in combination in order to achieve such a goal. Laser spectroscopic techniques based on optical cavities are used to build a high resolution spectrometer covering a large spectral range capable of selectively detecting low levels of gaseous compounds of interest, especially those of medical or environmental significance. Work in both the near- and mid-infrared is presented, including much of the initial, developmental work which was conducted in the former region. The thesis begins with an overview of both narrowband and broadband near-infrared radiation sources, with a particular emphasis on commonly available diode lasers (DLs). A novel laser source, the digital supermode distributed Bragg reector (DS-DBR) laser, is introduced as a useful laser source for spectroscopy, combining the usual benefits of telecom DLs with a wide tunability (1563 – 1613 nm). The laser can be operated in an internal or external ramping mode, allowing the output wavelength to be scanned or stepped across a desired region. The observation of mode-hopping during the application of the scanning methodology is examined and rationalised. The ability of the DS-DBR laser to perform high resolution spectroscopy over its entire spectral coverage is demonstrated by recording spectra of carbon dioxide (CO<sub>2</sub>) over this range, covering transitions from two of the four Fermi resonance components of the 3ν<sub>1</sub> + ν<sub>3</sub> combination band. The results of conducting wavelength modulation spectroscopy on CO<sub>2</sub> are also reported. A system developed for performing cavity ring-down spectroscopy (CRDS), capable of the real-time retrieval of ring-down times (RDTs), is presented and discussed. The outcomes of initial tests performed with a conventional DL at 1557 nm, to study a calibrated mixture of CO<sub>2</sub> in air at various pressures, are given. In addition, the results of combining this system with the DS-DBR laser are discussed. The bandwidth of the DS-DBR laser was found to be larger than that of a standard DFB DL, resulting in the presence of noisy cavity modes. Despite this, the acquisition of reproducible RDTs is demonstrated, with single wavelength studies of an evacuated cavity at 1605.5 nm yielding a RDT of 24.54 ± 0.04 µs and Allan variance calculations signalling an attainable minimum detectable absorption coefficient, α<sub>min</sub>, of 2.8 x 10<sup>-10</sup> cm<sup>-1</sup> over 20 s. The ability to perform CRDS across the whole DSDBR laser wavelength range without the need for cavity re-alignment is illustrated, and studies conducted on CO<sub>2</sub> in air, calibrated mixtures and breath are reported. Investigations are also described into the accurate determination of the <sup>13</sup>C/<sup>12</sup>C ratio in exhaled CO<sub>2</sub> undertaken using CRDS and cavity enhanced absorption spectroscopy (CEAS) on CO<sub>2</sub> isotopologues, an approach which can be utilised as a diagnostic aid in determining Helicobacter pylori infection. The focus of the thesis then moves to the mid-infrared, to describe quasi phase matching difference frequency generation (QPM-DFG) and its use to generate laser light at 3 µm by optically mixing near-infrared DLs. The theory behind this non-linear optical interaction is outlined, and the construction of a free-space QPM-DFG system using periodically poled lithium niobate is detailed and characterised. This DL-based QPM-DFG arrangement has been coupled with the CRDS system developed to create a mid-infrared CRD spectrometer. The results of single wavelength studies indicate RDTs of ~ 6 µs and an achievable αmin of 2.9 x 10<sup>-9</sup> cm<sup>-1</sup> over 44 s for an evacuated cavity. Spectroscopic investigations carried out on methane (CH<sub>4</sub>), acetone and deuterium are documented; for the latter species, Dicke narrowing of the electric quadrupole ν(1←0) Q(2) transition at 2987.29 cm<sup>-1</sup> is observed and the integrated absorption cross-section for the same transition measured as 2.29 ± 0.03 x 10<sup>-27</sup> cm<sup>2</sup>cm<sup>-1</sup>molec<sup>-1</sup>. The results of modifications made to the system, namely the use of a more powerful Nd:YAG laser as the pump radiation source, as well as a faster detector combined with a variable amplifier, are presented; these include the observation of an improved optimal α<sub>min</sub> of 6.4 x 10<sup>-10</sup> cm<sup>-1</sup> over 151 s for an empty cavity. Finally, work utilising the DS-DBR laser as one of the near-infrared sources for the QPM-DFG set-up is presented. This configuration generates radiation covering a wide mid-infrared range (3130 – 3330 nm) and has been used to perform direct absorption and wavelength modulation spectroscopy on ro-vibrational transitions within the fundamental ν<sub>3</sub> (F<sub>2</sub>) band of CH<sub>4</sub>. The spectrum of methanethiol (CH<sub>3</sub>SH) over this region has also been investigated, with preliminary studies identifying a feature at 3040 cm<sup>-1</sup> as a potential indicator for monitoring this biomarker in breath. The results of coupling this mid-infrared radiation with an optical cavity to perform CEAS combined with phase sensitive detection are subsequently reported. Studies were conducted on calibrated CH<sub>4</sub> mixtures and ambient air to examine two transitions of the fundamental ν<sub>3</sub> (F<sub>2</sub>) band of CH<sub>4</sub> in order to characterise the system: effective path lengths of ~ 700 m and α<sub>min</sub> of 6.2 x 10<sup>-8</sup> cm<sup>-1</sup> over 8 s were found. The <sup>R</sup>Q<sub>4</sub> CH<sub>3</sub>SH absorption feature at 3040 cm<sup>-1</sup> was also further studied with this system using prepared samples of CH<sub>3</sub>SH in N<sub>2</sub> at different concentrations, yielding a CH<sub>3</sub>SH detection limit of 2.4 ppm at 19 Torr. The potential of such a cavity-based, DS-DBR sourced, QPM-DFG mid-infrared spectrometer for trace gas sensing having thus been demonstrated, possible improvements that could be implemented to increase the sensitivity of the system are then discussed.
189

The stated preference technique for estimating the modal split inhome-work journey in the mid-levels

Woo, Kwong-ming, William., 胡廣明. January 1994 (has links)
published_or_final_version / Transport Studies / Master / Master of Arts
190

Examining Perceptions of Black Administrators in Higher Education Regarding Administrative Leadership Opportunities

Thompson, Renita Taylor 01 January 2016 (has links)
In spite of the research highlighting the significance of the presence of Black administrators to the success of Black students, there continue to be noticeable disparities in the representation of Black and White administrators in higher education. The racial and ethnic makeup of institutions of higher education does not reflect the demographics of the U.S. population. Black administrators are disproportionately underrepresented throughout academe, and are even more sparse at the executive levels of leadership. The purpose of this study was to examine the perceptions and attitudes of mid-level Black administrators with respect to progressing into executive-level administrative positions at predominantly White institutions. Relevant scholarly literature on mid-level administrators, career advancement, and racial barriers in higher education were examined. Three major tenets of Critical Race Theory (CRT) in education were used as a theoretical lens to examine racial inequities and disparities Black administrators experience in the academy. To address the research question and to explore the subjective viewpoints of the participants, Q methodology was utilized. After IRB approval, purposive sampling was used to recruit 40 Black mid-level administrators to participate in the study. All participants held one of the following titles: Director, Associate Director, Assistant Director, Dean, Associate Dean, Assistant Dean, and Manager. They each worked for a bachelor’s degree granting public college or university. In addition to their title, the participants had to have earned at minimum a master’s degree. Semi-structured interviews were held with 8 of the 40 participants. Content from interviews, questionnaires, and literature contributed to concourse development. By removing redundant and useless items, the concourse was refined and condensed from 90 statements to develop a Q sample of 41 statements. Through an online process, 40 participants sorted the 41 item Q sample that represented the full gamut of perspectives regarding the subject of career progression in higher education. In the sorting process, the participants ranked the statements based on their personal views and beliefs. A review and analysis of data resulted in five factors that categorize and represent the subjective viewpoints of the participants. The factor arrays, post-sort comments, distinguishing statements, and demographic details aided in interpreting and naming each factor. The five factors were named: Factor 1: The Disconnected, Factor 2: The Disadvantaged, Factor 3: The Disrespected, Factor 4: The Dismissed, and Factor 5: The Disinterested. Each factor was analyzed and interpreted to provide descriptions of how Black administrators perceive career progressions in higher education. Recommendations to expand the study were included.

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