Browsing Honors Research Fellows and Undergraduate Research Scholars Theses by Title
Now showing items 1-20 of 575
Next Page →-
Kim, Kun Mo (May 2011)[more][less]
Abstract: This thesis presents the design of a 20 MHz bandwidth 3rd-order continuous-time low-pass sigma-delta analog-to-digital converter with low-noise and low-power consumption using TSMC 0.18 μm CMOS technology. The bandwidth of the system is selected to be able to accommodate WiMAX and other wireless network standards. A 3rd-order filter with feed-forward architecture is selected to achieve low-power consumption as well as less complexity. The system uses 3-bit flash quantizer to provide fast data conversion. The current-steering DAC not only achieves low-power and less current sensitivity, but also it helps directly inject the feedback signal without additional circuitries. In order to avoid degradation of the overall performance, cross-coupled transistors are adopted to reduce the current glitches. The proposed system achieves a peak SNDR of 65.9 dB in 20 MHz bandwidth, and consumes 31.735 mW from a 1.8 V supply. The entire circuit is driven by a sampling rate at 500 MHz. The measured in-band IM3 of this thesis is -69 dB with 600 mVp-p two tone signal peak-to-peak voltage.
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2011-05-9651 Files in this item: 1
KIM-THESIS.pdf (1.833Mb) -
Catanach, Therese A. (August 29, 2007)[more][less]
Abstract: Based on museum-held and field-collected specimens new data are presented regarding the distribution, adult phenology and first-instar larva of the uncommon green lacewing Abachrysa eureka. It was found that this species is broadly distributed across the southeastern United States, from Texas to the east coast south to Florida and north to South Carolina. There are multiple short duration emergence periods which vary with latitude. This species appears to be a typical chrysopid in various biological aspects, such as the occurrence of a stalked egg and placement of debris on the backs of larva.
URI: http://hdl.handle.net/1969.1/5709 Files in this item: 1
CatanachTAthesis26iv2007.pdf (336.2Kb) -
Evetts, Elizabeth A.; Peterson, Jacqueline A. (September 30, 2009)[more][less]
Abstract: The above- and below-ground litter from fallen foliage and root exudates and their decomposition has an impact on forest soil. The objective of this research project was to determine the effect of above- and below-ground litter manipulation on the retention and release of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), nitrate and ammonium in the soil profile at 0-5 and 5-15 cm depths. The soils were obtained from a Long Term Ecological Research site in the Sikfokut Forest in Hungary. The site is a mature oak forest and the soil has no organic layer; the leaf litter sits directly on the A horizon. There are six treatments applied to the soil: doubling of annual leaf litter (DL), doubling of annual wood litter (DW), removal of annual leaf litter (NL), removal of roots (NR), removal of leaf and roots (NI) and control (C). Each plot is 7 x 7 m, and each soil sample taken was 15 x 15 cm square. A stock solution of leaf litter was added in different concentrations to soils from each treatment in a 50 mL centrifuge tube. Because I was investigating retention or release of carbon and nitrogen, I inverted the tube gently over a period of 2 hours prior to centrifugation and removal of supernatant. The supernatant solution was analyzed for DOC, DON, ammonium and nitrate to determine retention and release values for each dependant upon the different treatments. The results of the study were interesting. Dissolved organic nitrogen was neither retained nor released in the 0-5 cm layer for any treatment yet nitrate, typically considered a mobile anion showed retention and release in this layer. In the 5-15 cm layer we had no retention or release of nitrate but dissolved organic nitrogen was retained and released between the solid and solution phases.
URI: http://hdl.handle.net/1969.1/88040 Files in this item: 1
Evetts_Approved_Thesis.pdf (131.3Kb) -
Kolb, Frances Bailey (August 3, 2007)[more][less]
Abstract: This paper examines the influence of colonial policy and intercultural relations on the development of Acadian settlement in Louisiana between 1765 and 1785, spanning a portion of both French and Spanish colonial periods. Research has included an array of secondary sources, books, articles and maps, as well as a variety of primary sources, including published collections and archival material. Analysis of sources reveals two stages of Acadian settlement: the determination of physical location of settlements, and the characteristics, such as economic, demographic, and social, pertaining to the settlements. Political and social forces within colonial Louisiana affected the two stages of Acadian settlement differently. Colonial settlement and defense policies and Acadian culture influenced the location of settlements most strongly, while Acadian relations with other groups in Louisiana shaped the characteristics that the settlements developed during the 1770s. Acadian settlement indicates the imperial policies of France and Spain and the effect of these policies on the colonial population of Louisiana.
URI: http://hdl.handle.net/1969.1/5700 Files in this item: 1
Kolb_Frances_Fellows.pdf (957.5Kb) -
Skeeles, Angela D (Texas A&M University, 2003)[more][less]
Abstract: Today, natural systems are undergoing drastic human-induced changes and losses of biodiversity. During this time of change it is extremely important that we understand the underlying mechanisms controlling the structure and composition of biotic communities. Small mammal communities have been studied extensively in arid regions (Brown et al. 2000), but few studies have been conducted in tropical regions. In 1957 Hutchinson proposed niche division as a means of co-existence of similar species. In 1974 Schoener proposed that the dietary, spatial, and temporal were the three main axes along which niche division may occur. This study evaluated the temporal patterns of the rodent communities at two sites in El Cielo Biosphere Reserve, Tamaulipas, Mexico. The first site was located in the Tropical Sub-Deciduous Forest (TSDF) region of the reserve. Six rodent species were trapped during interval trapping: Liomys irroratus (Heteromyidae), Peromyscus levipes (Muridae), Peromyscus leucopus (Muridae), Baiomys taylori (Muridae), Sigmodon hispidus (Muridae), and Oryzomys couesi (Muridae). All species at both sites are nocturnal and granivorous. We used chi-square and G-test analyses and rejected our null hypothesis (Time periods during the night were utilized equally) for all species except for P. leucopus, which had an extremely small sample size. We constructed a null model using Gotelli's Ecosim program against which to test Pianka's niche overlap index, and found that p (observed <= expected) = 0.91 (Gotelli and Entsminger 2001). Likewise, at the second site, located in the Cloud Forest (CF) region, we rejected our null hypothesis for both species (P. levipes and P. ochraventer (Muridae)). P (observed <=expected)=0.87. We concluded that there is a very small chance the patterns observed in either site are random, and thus there is likely an underlying mechanism shaping these patterns. We also observed that O. couesi and L. irroratus overlapped in their spatial and dietary niches, but were separated by their temporal niche utilization. The temporal niche aspect is rarely included in the many studies focusing on dietary and spatial niches. There are still many aspects of activity patterns that are poorly understood.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaves 25-30).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2003-Fellows-Thesis-S62 Files in this item: 1
2003 Fellows Thesis S62.pdf (1.203Mb) -
Jones, Christopher V (Texas A&M University, 1999)[more][less]
Abstract: Automatic motion planning has applications in many areas such as robotics, virtual reality systems, and computer-aided design. Although many different motion planning methods have been proposed, most are not used in practice since they are computationally infeasible except for some restricted cases, e.g., when the robot has very few degrees of freedom (dof). For this reason, attention has focussed on randomized or probabilistic motion planning methods. When many motion planning queries will be performed in the same environment, then it may be useful to pre-process the environment with the goal of decreasing the difficulty of the subsequent queries. Examples are the roadmap motion planning methods, which build a graph encoding representative feasible paths (usually in the robot's configuration space, which is the parametric spacer representing all possible positions and orientations of the robot in the workspace). Indeed, recently several probabilistic roadmap methods (PRMs) (including our group's obstacle-based PRM ) have been used to solve many difficult planning problems involving high-dimensional C-spaces that could not be solved before. However, if the start and goal configurations are known a priori, only one (or a very few) queries will be performed in a single environment, then it is generally not worthwhile to perform an expensive preprocessing stage, particularly if there are time constraints as in animation or virtual reality applications. In this case, a more directed search of the free configuration space is needed (e.g., as opposed to roadmap methods which are designed to try to cover the entire freespace). Motion planning methods that operate in this fashion are often called single shot methods. In our current work, we are developing an adaptive framework for single shot motion planning (i.e., planning without preprocessing). This framework can be used in any situation, and in particular, is suitable for crowded environments in which the robot's free C-space has narrow corridors. The main idea of our framework is that one should adaptively select a planner whose strengths match the current situation, and then switch to a different planner when circumstances change. This approach requires that we develop a set of planners, and characterize the strengths and weaknesses of each planner in such a way that we can easily select the best planner for the current situation. Our experimental results show that adaptive selection of different planning methods enables the algorithms to be used in a cooperative manner to successfully solve queries that none of them would be able to solve on their own.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaves 19-21).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-1999-Fellows-Thesis-J65 Files in this item: 1
1999 Fellows Thesis J65.pdf (672.2Kb) -
Delgadorodriguez, Michelle Renee (Texas A&M University, 1998)[more][less]
Abstract: Attention Deficit Disorder (ADD/ADHD) is a highly heritable behavioral disorder. Frequently a child with ADHD is labeled as a problem child instead of a child with a problem. Furthermore, there are three subtypes of ADHD. The nuances of each of the ADD/ADHD subtypes require different considerations when devising a plan of action to assist these children in functioning in the classroom, among their peers, and in the world. Inattentive (I) children s social skills are relatively age appropriate; however, their classroom skills and ability to succeed in performing tasks is diminished relative to same-aged peers. Hyperactive/Impulsive (HI) children perform better than other ADHD students in classroom skills, but their social skills (e.g., ability to interact with both peers and others) are diminished. Combined Type (CT) children manifest qualities of both I and HI children (e.g., problems with classroom skills and social skills). Through survey mailouts, information regarding parental perceptions of effectiveness of various treatments was obtained. The treatments examined were medications, school programs, and communications between teachers and parents, physicians and parents, and teachers and physicians. This information was then compiled and analyzed. In all cases the quality of communication was reported as a moreimportant factor than frequency of communication in regard to level of usefulness. Parents repeatedly emphasized the importance of educated awareness of ADHD and its treatment options as qualities teachers lack. Parents wanted teachers to be required to study learning and social disorders and to be trained in how to help children with these special needs. Another major factor affecting children in this study is limited progress due to the lack of cooperation of schools to provide support for ADHD children because they do not believe ADHD qualifies under The Rehabilitation Act of 1973 section 504 (which in 1991 was clarified by the U.S. Department of Education to include children with ADD) without co-morbid complications. Children with ADD are also protected by part B of the Individuals with Disabilities Education Act (IDEA). Both section 504 and IDEA are designed to ensure equal educational opportunities for all levels oflearners. U.S. Department of Education to include children with ADD) without co-morbid complications. Children with ADD are also protected by part B of the Individuals with Disabilities Education Act (IDEA). Both section 504 and IDEA are designed to ensure equal educational opportunities for all levels of learners.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references: leaf 59.
URI: http://hdl.handle.net/1969.1/ETD-TAMU-1998-Fellows-Thesis-D453 Files in this item: 1
1998 Fellows Thesis D453.pdf (1.588Mb) -
LaFleur, Adrienne; Charlton, William (September 17, 2007)[more][less]
Abstract: An algorithm was developed that uses measured isotopic ratios from fission product residue following the detonation of a high-enriched uranium nuclear weapon to compute the original attributes of the material used in the device. The specific attributes assessed are the uranium isotopics (considering 234U, 235U, 236U, and 238U) and the enrichment process used to create the material (e.g., gaseous diffusion, gas centrifuge, etc.). Using the original attributes of the weapon significantly increases the probability of identifying the perpetrator of the attack. In this study, research was conducted to perform sensitivity analysis of the calculated values, analyze alternate enrichment methods, determine the source (uranium mine) from which the feed material was taken and assess potential “spoofing” techniques. The purpose of this research was to verify that the analytical method developed would remain valid for a multitude of variations that could be used to disguise the origin of the nuclear material in the device. It is envisioned that this methodology could serve as a preprocessing step to a more computationally intensive and more accurate system in the event of a nuclear terrorist attack.
URI: http://hdl.handle.net/1969.1/5720 Files in this item: 1
2007 LaFleur Thesis.pdf (1.048Mb) -
Baumbach, Christopher Lloyd (Texas A&M University, 2001)[more][less]
Abstract: Based on a study by Bushman and Baumeister (1998), we hypothesized that high global self-esteem and high collective self-esteem should be predictive of greater aggressive. We also hypothesized that participants with high narcissistic tendencies should be more likely to aggress than those with less narcissistic tendencies or lower self-esteem. Finally, we believe that men (in general) should more likely aggress in response to a perceived threat (a personal insult) than women in the same situation. In the present study, participants wrote an essay and then received a manipulated evaluation (either positive or negative) of the essay supposedly from another participant. They were later given the chance to aggress against their evaluator. Global self-esteem, collective self-esteem, and narcissism did not predict aggression. However, males were more likely to be aggressive than females, particularly in the negative evaluation condition.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaves 22-27).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2001-Fellows-Thesis-B394 Files in this item: 1
2001 Fellows Thesis B394.pdf (1.498Mb) -
Chateau, Morgan (September 17, 2007)[more][less]
Abstract: Many neurodegenerative diseases are associated with protein misfolding where the protein forms β-sheet rich polymers called amyloid. Alzheimer’s disease (AD) is an amyloid aggregation disease involving the Aβ(1-42) peptide fragment of the Amyloid Precursor Protein (APP) in the nervous tissue of the brain. Within the peptide there are regions thought to be more critical for amyloid formation; one of which is Aβ(25-35). This sequence has the ability to form amyloid at sufficient peptide concentrations. Within this region, residues 33-35 have been found by terminal deletions to be a core region (1), the residues necessary for amyloid formation. Using Cys-scanning mutagenesis the estimated core region (31-34) is slightly different. Previous papers have shown, the peptide loses the ability to form amyloid fibrils when the sequence of amino acids is changed (2). For this experiment, four different Aβ(25-35) sequences were tested, each having the same composition but a different sequence. FPLC was used in conjunction with Thioflavin-T fluorescence to monitor amyloid development. The results showed a definite effect on amyloid formation as compared to wild type. Sequence S-N showed nearly no change in behavior. Sequence S-M appeared to loose all amyloid forming ability. The remaining two sequences were unable to remain in solution long enough to be accurately tested.
URI: http://hdl.handle.net/1969.1/5722 Files in this item: 1
Final 2007 Spring Thesis.pdf (171.1Kb) -
Hood, Michael (Texas A&M University, 2004)[more][less]
Abstract: Economists have long studied innovation and its effects on business cycles. Economist Joseph Alois Schumpeter (1883-1950) was the first economist to thoroughly discuss these ideas in his Theorie der wirtschaftlichen Entwicklung, published in 1911 (English translation: The Theory of Economic Development, 1934). This paper focuses on three issues: defining innovation, defining and identifying business cycles, and determining which innovations caused which business cycles. The first section introduces the concepts of innovation and invention. The second section discusses the business cycles and highlights general causes of business cycles. The final section details the history of the iron, steel, aluminum, and pharmaceutical industries and incorporates the available business and economic data (output, productivity, inventories, and capital investment) required to answer the central question: which innovations caused which business cycles? The iron industry, examined over the sixteenth and seventeenth centuries, reveals that its relationship to the business cycle is likely significant but was difficult to quantify because of limited data. An examination of the steel industry from the post-Civil War period to the early twentieth century follows. The steel industry had a significant effect on the business cycle and seemed to direct the business cycle during the growth in railroad mileage. Steel was a huge and indispensable industry for most of the 20[th] century so it makes a very important case to study. The aluminum industry is relevant to examine because the process for making aluminum has remained the same since the American inventor, Charles Hall, patented his method in 1889. The contribution of aluminum was significant because of the introduction of the large-scale electrical generators needed to produce aluminum. Finally, the paper focuses on the contribution of the pharmaceutical industry to the business cycle. The pharmaceutical industry is important to this study because it has already proved to be a major source of innovation and is an industry that will continue to play a significant role in the American economy. The findings reveal the contribution from this industry was most significant in the post-World War II era of research and development. The paper concludes with suggestions for improving and expanding this innovation and business cycle study.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaves 34-36).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2004-Fellows-Thesis-H66 Files in this item: 1
2004 Fellows Thesis H66.pdf (1.170Mb) -
Qiu, Xiaofan (September 17, 2007)[more][less]
Abstract: As portable electronic devices become a part of daily life, it creates a huge market for electronic components for those battery driven devices. Low-dropout (LDO) voltage regulator is an important part that provides steady DC supplies for other components. Low power, low noise and high stability are the desired features of a regulator. Detailed analyses on CMOS LDO design and the designs of two different compensation schemes for LDO are presented in this thesis. Experimental results of the designed compensation programmable low-power low-dropout (LDO) Voltage Regulator, in comparison with an existing compensated LDO, are also presented. The designed compensation implementation demonstrates a fast transient response and high stability in all programmable output levels. Testing chip fabricated in a standard 0.35 CMOS technology provided the important parameters of the regulator, e.g. transient response, load regulation, line regulation, power supply rejection ratio (PSRR).
URI: http://hdl.handle.net/1969.1/5721 Files in this item: 1
Research_Scholar_Thesis_Xiaofan_Qiu.pdf (317.1Kb) -
Leveridge, Yolanda Kay (Texas A&M University, 2002)[more][less]
Abstract: It is important to the profession of architecture that the educational aspect of architecture be suitable enough to maintain standards within the profession. The design process is one of the more crucial components to the understanding of architectural pedagogy. Several schools of thought exist on architectural design process. Consequently, several different basic design processes are taught within architecture programs. This paper analyzes two different design processes: one experienced through an academic project with real clients overseen at Texas A&M University's College of Architecture; the other experienced in a senior level design studio as part of a four year Bachelor's degree from the university. As criterion for evaluation, the project will be analyzed in terms of scope, quality, and time. Scope denotes the scale of the project. Quality simply refers to the projects' practicality and aesthetics as reflected in the design. Time refers not to the amount of time spent on the project totally, but to the amount of time spent on specific aspects of the design process. Using these criterions, an analysis of the design processes is conducted in order to identify the inherent differences between both processes, and to explain the reasons behind these differences. From further analysis of literature related to the subject and through my own documented observations, I suggest why the differences in structure of the two design processes are critically important to the design in each instance and suggest my opinion on a better and more effective method of design.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaves 29-32).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2002-Fellows-Thesis-L474 Files in this item: 1
2002 Fellows Thesis L474.pdf (2.110Mb) -
Hart, Jason Frazier (Texas A&M University, 2000)[more][less]
Abstract: The extent of damage and casualties in Midwest cities such as St. Louis during an earthquake caused by the New Madrid fault system will be due in part to the performance of buildings. Dynamic nonlinear analysis of a reinforced concrete building not designed for seismic loads is one method used to assess an existing building's ability to withstand an earthquake. Many researchers have studied the earthquake resistance of structures, and often analytical studies have used recorded ground motions such as the 1940 El Centro, California, earthquake. Reports from past experimental studies and observations of damage caused by seismic events have been valuable for evaluating the performance of specific components of a building and overall performance of buildings subjected to this type of ground motion. This research study differs from previous research in that it focuses on the Midwest United States and uses synthetic ground motions developed specifically for an earthquake that would occur in this region. Research of the performance of a five-story, reinforced concrete, moment frame building in the Midwest United States is discussed in this thesis. In order to estimate the performance of a typical building in this region, the building was designed based on codes from the mid-1980's, prior to the seismic design standards of today requiring a ductile structural system. The study building's performance is evaluated using the dynamic nonlinear analysis computer program DRAIN-2DM. Dynamic analysis of the structure is performed using synthetic ground motions for the Midwest produced by Y.K. Wen of the Mid-America Earthquake Center. The analyses of the building were performed using twenty ground motion records. Ten ground motions are for earthquakes with two percent probabilities of exceedance in 50 years, and ten are for ten percent probabilities of exceedance in 50 years. Results of the analyses are discussed in this thesis and are used to estimate the damage to the structure.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaves 53-55).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2000-Fellows-Thesis-H367 Files in this item: 1
2000 Fellows Thesis H367.pdf (1.932Mb) -
Tydlacka, Jonathan Michael (Texas A&M University, 2002)[more][less]
Abstract: The purpose of this project was to perform micro-simulation analyses on intersections near Highway-Railroad Grade Crossings to determine if controlling mean train speed and train speed variability would improve safety and reduce delays. The first of two objectives for this project required the completion of a micro-simulation model and the subsequent checking of the model for errors and accuracy. The second part consisted of train speed sensitivity analyses on mean train speed and train speed variability. A micro-simulation model of the Wellborn Corridor in College Station, Texas was created using VISSIM. The model was run ten times in each of the nine train speed distributions. Average delay was collected for each of the four intersections in the model. Additionally, the model was run with alternate train detection distances and select train speed distributions, and average delay was again collected. For each train speed distribution and intersection, delays were compared using the t-test with a 95% confidence interval. Comparisons were made against train speed distributions with either the same mean speeds, the same standard deviations, the base train speed, or the same distribution with a different train detection distance. Furthermore, these comparisons were made for each of the four lo-minute intervals of the simulation. Significant differences were found only in the second time interval, when the trains were present. Some significant differences were found when the mean train speeds were altered, and these were more prevalent at the high volume intersection, George Bush Dr. However, the number of statistically different comparisons was still not considered substantial. Ultimately, it was found that manipulating the train detection distance, the mean train speed, or the train speed standard deviation did not have a significant effect on the average delay for the traffic layout that was modeled for this particular corridor.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaf 16).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2002-Fellows-Thesis-T92 Files in this item: 1
2002 Fellows Thesis T92.pdf (1.312Mb) -
Pritchard, Megan (July 11, 2006)[more][less]
Abstract: Gas-cooled nuclear reactors have been receiving specific attention for Generation IV possibilities due to desired characteristics such as relatively low cost, short construction period, and inherent safety. Attractive inherent characteristics include an inert, single phase helium coolant, refractory coated fuel with high temperature capability and low fission product release, and graphite moderator with high temperature stability and long response times. The passively safe design has a relatively low power density, annular core, large negative temperature coefficient, and passive decay heat removal system. The objective of the U.S. DOE NERI Project is to assess the possibility, advantages and limitations of achieving ultra-long life VHTR (Very High Temperature Reactor) configurations by utilizing minor actinides as a fuel component. The present analysis takes into consideration and compares capabilities of pebble-bed core designs with various core and reflector configuration to allow spectrum shifting for advanced actinide fuels. Whole-core 3D models for pebble-bed design with multi-heterogeneity treatments in SCALE 5.0 are developed to compare computational results with experiments. Obtained results are in agreement with the available HTR-10 data. By altering the moderator to fuel ratio, a shift in the spectrum is observed. The use of minor actinides as fuel components relies on spectrum shifting capabilities. Actinide fueled VHTR configurations reveal promising performance. With an optimized pebble-bed model, the spectrum shifting abilities are apparent and effects of altered moderator to fuel ratio, and Dancoff factor are investigated. This will lead to a facilitated development of new fuel cycles in support of future operation of Generation IV nuclear energy systems.
URI: http://hdl.handle.net/1969.1/3663 Files in this item: 1
MPritchardUGRS.pdf (628.3Kb) -
Ahmed, Taahir (May 2011)[more][less]
Abstract: The theory of sensori-computational circuits provides a capable framework for the description and optimization of robotic systems, including on-line optimizations. This theory, however, is inadequate in that it does not account for uncertainty in a robot’s environment, sensing, and control. In order to allow meaningful optimization of robotic systems, a method for estimating the output uncertainty of an s-circuit in terms of the uncertainty in its input is formulated. This method is expressly designed to have low information requirements, to ensure that it is feasible to apply in practice. The method is subjected to experimental verification on two representational s-circuits, which confirms the validity of its predictions.
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2011-05-9649 Files in this item: 1
AHMED-THESIS.pdf (11.74Mb) -
Spivey, Sarah Elizabeth (Texas A&M University, 2000)[more][less]
Abstract: In 1998, pork prices fell to an all time low. Across the industry, concern was expressed for research as to what led to this price crash. Capacity constraints at the packer level have been a key area of concern. This study is an analysis of the effect of capacity constraints on pork prices. Ordinary least squares (OLS) models were run for both live and cutout prices. Capacity constraints were measured three ways: using a binary variable (0,1 dummy) and two continuous variables. One continuous variable was for the number of head slaughtered on the weekend, and the second continuous variable was found by using a ratio of slaughter during the weekends to slaughter during the 5-day workweek ("over-flow" ratio). The continuous variables used to measure capacity constraints were statistically significant explanatory factors in the regressions for hog and pork prices. The capacity constraints were estimated to have a different relationship with the prices at the farm level as compared with packer prices. Increasing capacity constraints is associated with a negative relationship to farm prices, and a positive relationship to packer prices. The measurement used for over-flow ratio, the ratio of weekend slaughter to slaughter during the 5-day workweek, did not generate different results than the continuous variable of weekend slaughter. The estimated coefficients for both continuous variables were more statistically significant than a dummy variable approach for the capacity constraint.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaves 31-32).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2000-Fellows-Thesis-S686 Files in this item: 1
2000 Fellows Thesis S686.pdf (1.085Mb) -
Pritchard, Megan; Tsvetkov, Pavel (September 30, 2009)[more][less]
Abstract: Gas-cooled nuclear reactors have been receiving specific attention for Generation IV possibilities due to desired characteristics such as relatively low cost, short construction period, and inherent safety. Attractive inherent characteristics include an inert, single phase helium coolant, refractory coated fuel with high temperature capability and low fission product release, and graphite moderator with high temperature stability and long response times. The passively safe design has a relatively low power density, annular core, large negative temperature coefficient, and passive decay heat removal system. The objective of the U.S. DOE NERI Project is to assess the possibility, advantages and limitations of achieving ultra-long life VHTR (Very High Temperature Reactor) configurations by utilizing minor actinides as a fuel component. The present analysis takes into consideration and compares capabilities of pebble-bed core designs with various core and reflector configuration to allow spectrum shifting for advanced actinide fuels. Whole-core 3D models for pebble-bed design with multi-heterogeneity treatments in SCALE 5.0 are developed to compare computational results with experiments. Obtained results are in agreement with the available HTR-10 data. By altering the moderator to fuel ratio, a shift in the spectrum is observed. The use of minor actinides as fuel components relies on spectrum shifting capabilities. Actinide fueled VHTR configurations reveal promising performance. With an optimized pebble-bed model, the spectrum shifting abilities are apparent and effects of altered moderator to fuel ratio, and Dancoff factor are investigated. This will lead to a facilitated development of new fuel cycles in support of future operation of Generation IV nuclear energy systems.
URI: http://hdl.handle.net/1969.1/88044 Files in this item: 1
MPritchardUGRS.pdf (659.8Kb) -
Kremkus, Mark Christian (Texas A&M University, 2001)[more][less]
Abstract: The goal of PERL MRI in its most basic form is single shot imaging without the need to rapidly switch gradients to encode spatial information into the signal. PERL MRI incorporates the application of the PERL field into the standard spin echo sequence following the excitation of spins, creating an initial phase pattern that causes echoes to form in the signal in the presence of a constant readout gradient. The echo train that occurs can be sampled and decoded into image data using reconstruction methods that are not discussed in this paper. The theoretical analysis of PERL MRI that will be discussed verifies the mathematical basis for the formation of a periodic signal resulting from cyclical coherence of the spins within a homogeneous sample. Theory also indicates a significant reduction in the maximum amount of coherence present in the PERL signal as compared to total coherence that occurs at the center of k-space, indicating that SNR may suffer with this technique. The effects of specific design parameters on the field generated by a proposed PERL coil design layout is discussed, and an experimental design is presented. The experimental PERL coil produces an approximation of the PERL field over a limited spatial region at the center of the coil structure. The PERL MRI pulse sequence was implemented by interfacing the experimental PERL coils to the slice selection gradient channel of a TecMag MRI console. Experiments were conducted using water phantom with varying amounts of PERL prephasing and readout gradient strengths, in an attempt to obtain data confirming the effects of the PERL imaging parameters on the PERL signal. These experiments were inconclusive as to the formation of a PERL echo train, but some form of cyclical coherence appeared to result. The evidence does not suggest that the PERL approach is robust when implemented with the experimental apparatus used in these experiments. Additional experiments are proposed, and possible explanations for the non-ideality of the experimental results are presented.
Description: Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.
Includes bibliographical references (leaf 32).
URI: http://hdl.handle.net/1969.1/ETD-TAMU-2001-Fellows-Thesis-K72 Files in this item: 1
2001 Fellows Thesis K72.pdf (1.438Mb)
Now showing items 1-20 of 575
Next Page →
Browse
