Electronic Theses, Dissertations, and Records of Study (2002– )

Permanent URI for this collection

http://hdl.handle.net/1969.1/2

Description

This collection contains Texas A&M University theses and dissertations written after 2002.

History

In 2002, the Texas A&M University’s Office of Graduate and Professional Studies (OGAPS) began accepting electronic submission of theses and dissertations. In 2004, electronic submission became a requirement, and OGAPS now also accepts electronically submitted records of study.

Access

Most theses and dissertations in this collection are open access. However, Texas A&M University students have a right to place their work under embargo in certain circumstances. The full-text of theses and dissertations under embargo is restricted until the embargo period has expired.

Website: Thesis and Dissertation Services

Browse

Now showing 1 - 20 of 24048

Untitled
(2019-07-11) ; Gezmis, Oguz; ; Papanikolas, Matthew A.; ; ; Masri, Riad; Young, Matthew P.; Zhang, Xianyang
Untitled
(2019-03-28) ; Barnhart, Elisabeth Creasman; ; Buschang, Peter H; ; ; Campbell, Phillip M; Julien, Katie; Noureldin, Amal; Svoboda, Kathy
Untitled
(2019-03-19) ; Baker, Mitchell Wade; ; Strong, Jr., Robert; ; ; Piña, Jr., Manuel; Hamie, Silva
Untitled
(2019-04-16) ; Ryan, Jennifer Michelle; ; Buschang, Peter H; ; ; Campbell, Phillip; Nourel-Din, Amal
Untitled
(2018-05-27) ; Kuzmin, Gleb Andrejevich; ; Akabani, Gamal; ; ; Ford, John; Wilson-Robles, Heather; Deveau, Michael; Kornegay, Joe; Lee, Choonsik
A 0.18-μm BICMOS 20-57 GHz Ultra-Wideband Low-Noise Amplifier Utilizing Frequency-Controlled Positive-Negative Feedback Technique
(2015-12-02) Luo, Yuan; Nguyen, Cam; Sánchez-Sinencio, Edgar; Kish, Laszlo; Mohanty, Binayak
Silicon based complementary metallic oxide semiconductor (CMOS) and Bipolar Complementary Metal Oxide Semiconductor (BiCMOS) radio frequency integrated circuits (RFICs), including microwave and millimeter-wave (MMW), are attractive for wireless communication and sensing systems due to their small chip size and facilitation in system-on-chip integration. One of the most important RFICs is the low-noise amplifier (LNA). The design of CMOS/BiCMOS wideband LNAs at MMW frequencies, especially those working across several decades of frequency, is challenging due to various issues. For instance, the device parasitic and inter-coupling between nearby elements in highly condensed chip areas limits the operating bandwidth and performance, and the conductive silicon substrates lead to the inevitable low quality factor of passive elements. In this work, a MMW BiCMOS ultra-wideband LNA across 20 to 57 GHz is presented along with the analysis, design and measurement results. To overcome the upper-band gain degradation and improve the in-band flatness, a novel frequency controlled positive-negative (P-N) feedback topology is adopted to modify the gain response by boosting the gain at the upper-band while suppressing that at the lower-band. To reduce overall power consumption, the first and second stages of the amplifier are stacked between supply voltage and DC ground to utilize the same DC current. At the output of amplifier, a shunt-peaking load stage is utilized to achieve wideband output matching. The designed ultra-wideband MMW LNA is fabricated in JAZZ 0.18-μm BiCMOS technology. It shows a measured power gain of 10.5 ± 0.5 dB, a noise figure between 5.1-7.0 dB, input and output return losses better than -10 and -15 dB, respectively, an input 1 dB compression point higher than -19 dBm, and an input third-order intercept point greater than -8 dBm. It dissipates 16.6 mW from 1.8 V DC supply and has a chip area of 700×400 μm^2.
1,1-bis(3-indolyl)-1-(p-substitutedphenyl) methanes induce apoptosis and inhibit renal cell carcinoma growth
(2009-06-02) York, Melissa Dawn; Stephen, Safe H; Burghardt, Robert C.; Phillips, Timothy D
Renal cell carcinoma (RCC) accounts for 85% of kidney cancer incidence in the US. Since 1950 there has been a 126% increase in kidney cancer incidence in the US. Thirty percent of new patients present with a localized easily treatable carcinoma while 30% of patients present with a high-grade metastatic carcinoma. Five-year survival rates for metastatic RCC is 6-12 months (Lipworth et al, 2006). Current disease treatment options for metastasis include chemotherapy and radiation (8% response rate), immunotherapy (15-30% response rate) and newly developed angiogenesis inhibitors which are in phase III trials (Staehler et el, 2005). In RCC cells, it has been shown that PPARγ agonists inhibit cell proliferation, induce apoptosis, and induce anti-angiogenic effects in vitro. Unlike most tumor types, PPARγ is downregulated in tissue samples from 47 RCC patients. However, in cell culture studies PPARγ expression does not correlate with growth inhibitory or apoptotic effects of PPARγ agonists in renal cell lines indicating that PPARγ independent responses may play a large role in actions associated with the PPARγ agonists (Yuan et al, 2006). 1,1-Bis(3'-indolyl)-1-(p-substitutedphenyl)methanes containing p-trifluoromethyl, p-t-butyl and p-phenyl substituents activate peroxisome proliferator-activated receptor (PPAR) and inhibit growth of ACHN and 786-0 renal cell carcinoma cell lines. PPAR is overexpressed in ACHN cells and barely detectable in 786-0 cells, and treatment with the t-butyl analog (DIM-C-pPhtBu) induces cell cyle inhibition. DIM-C-pPhtBu also induced several common PPAR-independent proapoptotic responses in ACHN and 786-0 cells, including increased expression of nonsteroidal antiimflammatory drug-activated gene-1 (NAG-1) and endoplasmic reticulum stress which activates death receptor 5 and the extrinsic pathway of apoptosis. In addition, DIM-C-pPhtbu (40 mg/kg/d) also inhibited tumor growth in an orthotopic mouse model for renal carcinogenesis, and this was accompanied by induction of apoptosis in renal tumors treated with DIM-C-pPhtBu but not in tumors treated with the corn oil vehicle (control). Thus, DIM-C-pPhtBu and related compounds represent a novel class of mechanism-based drugs that have potential for treatment of renal adenocarcinoma for which there are currently limited options for successful chemotherapy.
A 10-year content analysis to assess research theme areas in agricultural education: gap analysis of future research priorities in the discipline.
(2009-05-15) Edgar, Leslie Dawn; Briers, Gary; Rutherford, Tracy; Dooley, Kim; Boyd, Barry; Williams, Gary W.
The field of agricultural education relies on multiple research journals to disseminate findings. This study focused on a 10-year content analysis of research published in premier journals in agricultural education. The study ascertained primary research themes, types of research conducted, prolifically published authors, frequently cited authors, and frequently cited referenced works, and discussed how the formation and usage of research in agricultural education has changed from 1997 to 2006. The study sought assistance from agricultural educators to narrow the focus of the study and to ensure study content validity. A conceptual model, based on a thorough review of literature and a focus on the peer discipline areas of agricultural education, guided the study. The study utilized a field study and employed descriptive statistics. Premier agricultural education (AGED) journals were identified: the Journal of Agricultural Education (93%); Journal of International Agricultural and Extension Education (67%); Journal of Extension (63%); North American Colleges and Teachers of Agriculture Journal (48%); Journal of Applied Communications (41%); and Journal of Leadership Education (41%). The study identified primary and secondary research themes, prolific authorship, research methods and types, and frequently cited authors and referenced works in each of the identified premier AGED journals. The research used compiled data, from each of the research journals, to analyze the frequencies and gaps identified in the National Research Agenda [NRA]: Agricultural Education and Communication 2007-2010 (2007). Agricultural education in domestic and international settings: Extension and outreach was the research priority area noted as the most frequently identified in past research and no gaps were identified in the NRA. To continue to strengthen the agricultural education discipline, research from this study should be used to adjust research priority areas in the NRA and on the regional and state levels.
A 10Gb/s Full On-chip Bang-Bang Clock and Data Recovery System Using an Adaptive Loop Bandwidth Strategy
(2010-10-12) Jeon, Hyung-Joon; Silva-Martinez, Jose; Sanchez-Sinencio, Edgar; Li, Peng; Parlos, Alexander G.
As demand for higher bandwidth I/O grows, the front end design of serial link becomes significant to overcome stringent timing requirements on noisy and bandwidthlimited channels. As a clock reconstructing module in a receiver, the recovered clock quality of Clock and Data Recovery is the main issue of the receiver performance. However, from unknown incoming jitter, it is difficult to optimize loop dynamics to minimize steady-state and dynamic jitter. In this thesis a 10 Gb/s adaptive loop bandwidth clock and data recovery circuit with on-chip loop filter is presented. The proposed system optimizes the loop bandwidth adaptively to minimize jitter so that it leads to an improved jitter tolerance performance. This architecture tunes the loop bandwidth by a factor of eight based on the phase information of incoming data. The resulting architecture performs as good as a maximum fixed loop bandwidth CDR while tracking high speed input jitter and as good as a minimum fixed bandwidth CDR while suppressing wide bandwidth steady-state jitter. By employing a mixed mode predictor, high updating rate loop bandwidth adaptation is achieved with low power consumption. Another relevant feature is that it integrates a typically large off-chip filter using a capacitance multiplication technique that employs dual charge pumps. The functionality of the proposed architecture has been verified through schematic and behavioral model simulations. In the simulation, the performance of jitter tolerance is confirmed that the proposed solution provides improved results and robustness to the variation of jitter profile. Its applicability to industrial standards is also verified by the jitter tolerance passing SONET OC-192 successfully.
11th Grade Students' English Reading Motivation, Language Problems and Reading Achievement in Taiwan
(2012-07-16) Su, Jung-Hsuan; Dixon, L. Quentin; McTigue, Erin; Goetz, Ernest; Helfeldt, Jack
Motivation has been viewed as a very influential factor to successful reading for English as foreign language learners. Learners can be motivated to read English by extrinsic or intrinsic motivation, and the motivational orientations could also influence their reading achievement. However, language problems that EFL learners encounter while reading can affect their willingness to read as well as their reading achievement. The purpose of this study was to investigate Taiwanese EFL students’ English reading motivation and its relationship with perceived language problems and reading achievement. 302 11th grade students from an urban district in southern Taiwan participated in the study. Measures included an English reading comprehension test, an English reading motivation questionnaire, and a questionnaire regarding language problems in reading English. A factor analysis was used to determine the motivational orientations. Multiple regression and correlation analysis were performed to examine the relationship among reading motivation, language problems, and reading achievement. The results showed that: 1) Taiwanese senior high school students were largely motivated to read English by extrinsic motivation, specifically the importance and instrumental utility of reading English and the drive for recognition and competition, although they could also be motivated by intrinsic motivation to read English for knowledge and social purposes. Moreover, extrinsic motivation to read for compliance was significantly associated with their English reading scores. 2) While reading English, unknown idiomatic expressions and vocabulary were frequently reported language problems that influenced students’ willingness to read. Nevertheless, lack of grammar knowledge was generally not considered a big language problem to most of the students while reading. 3) Language problems in reading English and reading motivation were correlated, and motivation to read for compliance, grammar knowledge, and overall reading comprehension were significant predictors of students’ English reading scores. This study highlights the influential role of extrinsic motivation to EFL students in English reading and the importance of knowledge of vocabulary and idiomatic expressions in order to help understand the meaning of English texts. It provides implications for English teachers in designing appropriate curriculum that suits students’ needs and interests, and also suggestions for choosing proper reading materials.
142pr glass seeds for the brachytherapy of prostate cancer
(Texas A&M University, 2007-09-17) Jung, Jae Won; Reece, Warren D.; Braby, Leslie A.; Ford, John; Walker, Michael A.
A beta-emitting glass seed was proposed for the brachytherapy treatment of prostate cancer. Criteria for seed design were derived and several beta-emitting nuclides were examined for suitability. 142Pr was selected as the isotope of choice. Seeds 0.08 cm in diameter and 0.9 cm long were manufactured for testing. The seeds were activated in the Texas A&M University research reactor. The activity produced was as expected when considering the meta-stable state and epi-thermal neutron flux. The MCNP5 Monte Carlo code was used to calculate the quantitative dosimetric parameters suggested in the American Association of Physicists in Medicine (AAPM) TG-43/60. The Monte Carlo calculation results were compared with those from a dose point kernel code. The dose profiles agree well with each other. The gamma dose of 142Pr was evaluated. The gamma dose is 0.3 Gy at 1.0 cm with initial activity of 5.95 mCi and is insignificant to other organs. Measurements were performed to assess the 2-dimensional axial dose distributions using Gafchromic radiochromic film. The radiochromic film was calibrated using an X-ray machine calibrated against a National Institute of Standards and Technology (NIST) traceable ion chamber. A calibration curve was derived using a least squares fit of a second order polynomial. The measured dose distribution agrees well with results from the Monte Carlo simulation. The dose was 130.8 Gy at 6 mm from the seed center with initial activity of 5.95 mCi. AAPM TG-43/60 parameters were determined. The reference dose rate for 2 mm and 6 mm were 0.67 and 0.02 cGy/s/mCi, respectively. The geometry function, radial dose function and anisotropy function were generated.
A 16-Channel Receive Array Insert for Magnetic Resonance Imaging of the Breast at 7T
(2014-04-01) By, Samantha; McDougall, Mary P; Wright, Steven M; Grunlan, Melissa A; Lenox, Mark
Breast cancer is the second leading cause of cancer death among females in the United States. Magnetic resonance imaging (MRI) has emerged as a powerful tool for detecting and evaluating the disease, with notable advantages over other modalities, and the advent of ultra-high field strength scanners promises even more potential. In comparison to standard clinical MRI field strengths (1.5, 3.0 tesla), breast MRI at 7T provides increased signal-to-noise ratio (SNR) and spectral resolution. These benefits, however, are accompanied by significant challenges in hardware design, limiting the availability of commercial radiofrequency coils for 7T. The primary objective of this work is to enable the study of breast cancer at 7T with the development of a 16-channel receive array coil. The use of array coils to receive is standard in clinical MRI, as it provides higher SNR over a field of view than a single coil. In this case, when combined with the increased sensitivity provided by the high field strength, this will enable the ability to acquire images with higher resolution than could be achieved at 3T or 1.5T in clinically standard scan times. This has the potential to improve the morphological characterization of tumors and their involvement in the surrounding tissues. This thesis discusses the design and construction of a 16-channel receive array insert, characterization of its performance as an array, and comparison of the achievable SNR to a transmit-receive quadrature volume coil. With the 16-channel receive array insert, the results demonstrate a 6.5 times improvement in mean SNR and the ability to accelerate up to a reduction factor of 9 with a mean g-factor of 1.3. Finally, we present initial in vivo images acquired with the array, demonstrating the utility of the array coil through higher resolution imaging than the current protocols at lower field strengths.
16S rRNA-Based Tag Pyrosequencing of Complex Food and Wastewater Environments: Microbial Diversity and Dynamics
(2012-02-14) McElhany, Katherine; Pillai, Suresh D.; Walzem, Rosemary; Sturino, Joseph
Environmental microbiology has traditionally been performed using culture-based methods. However, in the last few decades, the emergence of molecular methods has changed the field considerably. The latest development in this area has been the introduction of next-generation sequencing, including pyrosequencing. These technologies allow the massively parallel sequencing of millions of DNA strands and represent a major development in sequencing technologies. The purpose of this study was to use both pyrosequencing and traditional culture-based techniques to investigate the diversity and dynamics of bacterial populations within milk and untreated sewage sludge samples. Pasteurized and raw milk samples were collected from grocery stores and dairies within Texas. Milk samples were analyzed by plating, pyrosequencing, and an assay for the presence of cell-cell signaling molecules. Samples were processed, stored, and then evaluated again for spoilage microflora. The results of this study showed that raw milk had a considerably higher bacterial load, more diversity between samples, and a significantly higher concentration of pathogens than pasteurized milk. Additionally, this study provided evidence for varying spoilage microflora between raw and pasteurized milk, as well as evidence for the production of cell-cell signaling molecules by bacterial organisms involved in milk spoilage. Four samplings of untreated sewage sludge were collected from wastewater treatment plants in seven different municipalities across the United States. Samples were subjected to quantification of selected bacterial organisms by culture and a pyrosequencing analysis was performed on extracted community DNA. The results of this study showed that untreated sewage sludge is inhabited by a huge diversity of microorganisms and that certain municipalities may have distinct bacterial populations that are conserved over time. Additionally, this study provided some evidence for seasonal differences in several of the major bacterial phyla. Lastly, this study emphasized the challenges of comparing results obtained by culture and pyrosequencing. In conclusion, this study showed that both milk and sewage are highly diverse, dynamic environments that can contain organisms of public health concern. The use of both culture-based methods and pyrosequencing in this study proved a complementary approach, providing a more comprehensive picture of both microbial environments.
16th Century Cast-Bronze Ordnance at the Museu de Angra do Heroismo
(Texas A&M University, 2004-09-30) Hoskins, Sara Grace; Crisman, Kevin; Castro, Filipe Vieira de; Dawson, Joseph G.
Within the collections of the Museu de Angra do Heroismo (Terceira Island, Azores, Portugal) are nine cast bronze guns from the 16th century. Most were raised from the seafloor between the 1960s and 1990s, but this study comprises the first in-depth research into their design and manufacture. The importance of this kind of study lies in the fact that ordnance is commonly found on shipwrecks of this time. A greater knowledge of guns will help provide information about the ships from which they came. Careful documentation and study of the Museu de Angra cannon will add greatly to their value as museum exhibits, by allowing museum patrons to better understand where the guns came from, how they were cast, and why they were important. This documentation adds to our knowledge of Western European gunfounding technology during the sixteenth century, as four different countries commissioned the guns: Portugal, Spain, France, and England. With detailed documentation and publication, the Museu de Angra bronze guns can be added to the bibliography of ordnance of this period, which will aid future researchers who encounter similar pieces. The Museu de Angra bronze guns, as symbols of the military and naval power of the countries that commissioned them, were sent aboard ships, into the field, and mounted on fortress walls. Bronze guns of this time period are particularly important, as bronze was an expensive commodity, and the demand for ordnance was increasing rapidly. Countries developed more effective ways to make use of iron for the founding of guns, and the use of bronze became more symbolic of wealth. The information that each gun contains includes both the cutting-edge military technology of the time and the artistic statement of the founder. Some of the finest metalwork of the period was displayed in cast bronze guns, and due to the founding techniques, no two are the same, making each an important piece of history.
The 1920s Texas Ku Klux Klan Revisited: White Supremacy and Structural Power in a Rural County
(2018-04-25) Walters, Katherine Kuehler; Blanton, Carlos K; Buenger, Walter; Moore, Wendy Leo; Hernandez, Sonia; McNamara, Sarah
The second Ku Klux Klan made its first public appearance in Texas at a United Confederate Veterans parade in October 1920, then quickly expanded across the state. Founder William J. Simmons created this organization as an exclusive, secretive fraternal group that both celebrated the original Ku Klux Klan (KKK) and responded to contemporary societal concerns of white native-born men and women in post-World- War-I America. Using a propaganda campaign, the organization preached the supremacy of a racialized Anglo-Saxon American identity, defined in terms of contemporary pseudo-scientific racial ideology as white, Protestant, native-born, and anti-radical, to recruit millions of members from across the nation within a few short years. Based on membership rolls and minutes of a Texas Klan chapter, this dissertation argues that, behind a façade of moral law and order, the Ku Klux Klan in rural Texas was a 1920s manifestation of a long-held racist ideology that utilized traditional practices of control through kinship, violence, and structural power to assert and protect white supremacy. It uses a localized case study approach to re-examine the second Ku Klux Klan in Texas, one of the largest and most powerful Klan organizations in the country, and challenge previous claims that the Texas KKK functioned more as a force for moral law and order and less as a white supremacy group. This particular Klan chapter, worked within the KKK’s Houston Provence, operated out of a rural county most noted for its plantation past and relatively recent end to Reconstruction, which firmly entrenched white structural control in the local economy, government, and social affairs. Based on an analysis of this Klan chapter’s individual members, their targets, and regional events, the Texas Klan used organizational power and vigilante violence to protect Anglo-Saxon white supremacy and maintain its centrality to the American identity. They conceptualized their nativistic and religious tenets through the lens of pseudo-scientific concepts of race that excluded Mexican and Japanese communities from whiteness. Furthermore, they utilized their members’ access to privileged structural power to plan and implement targeted attacks, coordinated between several chapters, on black and white individuals whose behavior they saw as threatening to the race, or for personal gain. They protected the organization’s extralegal violence through controlled police investigations and newspapers’ published narratives that surrounded the violence. When this failed, they utilized traditional white southern tools of white collective economic power and white respectability to undermine due process.
A 1Gsample/s 6-bit flash A/D converter with a combined chopping and averaging technique for reduced distortion in 0.18(mu)m CMOS
(Texas A&M University, 2005-08-29) Stefanou, Nikolaos; Sonkusale, Sameer; Georghiades, Costas; Parlos, Alexander; Silva-Martinez, Jose
Hard disk drive applications require a high Spurious Free Dynamic Range (SFDR), 6-bit Analog-to-Digital Converter (ADC) at conversion rates of 1GHz and beyond. This work proposes a robust, fault-tolerant scheme to achieve high SFDR in an av- eraging flash A/D converter using comparator chopping. Chopping of comparators in a flash A/D converter was never previously implemented due to lack of feasibility in implementing multiple, uncorrelated, high speed random number generators. This work proposes a novel array of uncorrelated truly binary random number generators working at 1GHz to chop all comparators. Chopping randomizes the residual offset left after averaging, further pushing the dynamic range of the converter. This enables higher accuracy and lower bit-error rate for high speed disk-drive read channels. Power consumption and area are reduced because of the relaxed design requirements for the same linearity. The technique has been verified in Matlab simulations for a 6-bit 1Gsamples/s flash ADC under case of process gradients with non-zero mean offsets as high as 60mV and potentially serious spot offset errors as high as 1V for a 2V peak to peak input signal. The proposed technique exhibits an improvement of over 15dB compared to pure averaging flash converters for all cases. The circuit-level simulation results, for a 1V peak to peak input signal, demon- strate superior performance. The reported ADC was fabricated in TSMC 0.18 ??mCMOS process. It occupies 8.79mm2 and consumes about 400mW from 1.8V power supply at 1GHz. The targeted SFDR performance for the fabricated chip is at least 45dB for a 256MHz input sine wave, sampled at 1GHz, about 10dB improvement on the 6-bit flash ADCs in the literature.
2-Dimensional Computational Fluid Dynamic Modeling on Comsol Multiphysics of Fischer Tropsch Fixed Bed Reactor Using a Novel Microfibrous Catalyst and Supercritical Reaction Media
(2019-10-17) Abusrafa, Aya Emhemed; Elbashir, Nimir; Linke, Patrick; Hassan, Ibrahim Galal
Fischer Tropsch synthesis (FT) is a highly exothermic catalyzed reaction to produce a variety of hydrocarbon products and value-added chemicals. To overcome the limitations associated with conventional FT reactors, utilizing high conductivity catalytic structures consisting of microfibrous entrapped cobalt catalyst (MFECC) has been proposed to enhance heat removal from the reactor bed. Additionally, utilization of supercritical fluids (SCF-FT) as a reaction media with liquid-like heat capacity and gaslike diffusivity have been employed to mitigate hot spot formation in FT reactors. The objective of the present study is to investigate the performance of FT Fixed bed/PB reactors operating using SCF-FT as a reaction media and MFECC structures using a conventional cobalt-based catalyst in terms of thermal management, syngas conversion, and product selectivity. A 2-D Computational Fluid Dynamics (CFD) model of an FT reactor was developed in COMSOL® Multiphysics v5.3a for three systems; nonconventional MFECC bed and conventional PB under gas-phase conditions (GP-FT) and non-conventional PB in SCF-FT media. The potential of scaling-up a typical industrial 1.5'' diameter reactor bed to a larger tube diameter (up to 4” ID) was studied as a first step towards process intensification of the FT technology. An advantage of increasing the tube diameter is that it allows for the use of higher gas flow rates, thus enabling higher reactor productivity and a reduction in the number of tubes required to achieve a targeted capacity. The high fidelity 2-D model developed in this work was built on experimental data generated at a variety of FT operating conditions both in conventional GP-FT operation and in SCF-FT reactor bed. Results showed that the MFECC bed provided excellent temperature control and low selectivity toward undesired methane (CHv4) and high selectivity toward the desired hydrocarbon cuts (C5+). For the 4'' diameter, the maximum temperature rise in the MFECC bed was always 2% below the inlet operational temperature. However, in PB the temperature can go up to 53% higher than the inlet temperature. This resulted in 100% selectivity toward methane and 0% selectivity toward the higher hydrocarbon cuts (C5+). On the other hand, the CH4 selectivity in the MFECC case was maintained below 24%, while the Cv5+ selectivity was higher than 70%. Similarly, the maximum temperature rise in SCF-FT for a 4” ID bed was just 15 K compared to ~800 K in GP-FT bed. The enhancement in thermal performance in the SCF-FT reactor bed is attributed to the high thermal capacity of SCF media (~2500 J/kg/K) compared to the GP media (~1300 J/kg/K), which resulted in the elimination of hotspot formation.
2-Dimensional Seismic Refraction Mapping Study of the Cretaceous-Paleogene Boundary Complex from the Brazos, Texas Section
(2012-07-16) Gowan, Joshua Smith; Everett, Mark E.; Mathewson, Christopher; Yancey, Thomas E.; Dickson, Bruce
Many scientific studies have been conducted on the Cretaceous-Paleogene boundary (KTB) in the Gulf coast region and, in particular, the Brazos River section in Falls County, Texas. Despite this, there remains much to be learned about the KTB and its depositional environment. Study of the KTB has been multidisciplinary, primarily in the fields of sedimentology and paleontology. Some researchers in these disciplines have questioned the consensus view of the placement of the KTB and subsequent interpretation of the timing of depositional events and mass extinction events. Geophysical methods have potential to provide additional understanding of the physical properties of the KTB. To date, study of the KTB has relied on point data and borehole information to create cross sections of the complex. Seismic refraction surveys can provide spatially continuous information on susburface horizons located adjacent to the KTB. In this study, seismic first-arrival traveltimes are processed with a tomographic modeling program to map the top of the hummocky cross-bedded sandstone (HCS), which is a key indicator of the deposition environment at the time of KTB boundary complex placement. The survey area is located at Cottonmouth Creek, a tributary of the Brazos River. Three seismic lines were surveyed, one across Cottonmouth Creek, and two parallel to the creek on either side. The data from the two parallel lines were processed using the 2-D seismic refraction tomography algorithm of Zelt and Smith. The reconstructed depth to the HCS in the survey area is approximately 6 m, with layer seismic velocities of 364, 1800, and 2200 m/s, respectively. Seismic tomography successfully mapped the HCS layer and reveals approximately 1 m amplitude undulations vertically and undulations on the order of several m horizontally. These variations are consistent with exposed surfaces of the HCS in the creek bed. Seismic refraction has been utilized successfully herein to map a key buried indicator, namely the top of the HCS layer, associated with the KTB complex. A detailed 3-D seismic refraction survey at this site is recommended to generate a high-resolution 2-D terrain map of the top of the HCS layer.
2.4 GHz Phase Locked Loop with DLL Based Spur Suppression Technique in 40nm CMOS
(2016-04-22) He, Yanying; Silva-Martinez, Jose; Entesari, Kamran; Hu, Jiang; Jo, Javier A
Phase locked loops (PLLs) are widely used as frequency synthesizers in modern communication systems because of the frequency accuracy and programmability of output frequency. Reference spur is an issue of concern in the PLL design as it merges the interference into the desired signal band. This study focuses on the design of PLLs with low reference spurs level. A PLL with 2.4 GHz output frequency is implemented in TSMC 40nm CMOS technology using a 1.1V supply. A delay locked loop (DLL) is inserted in the phase locked loop as a multiple phase generator, in order to move the fundamental spur to higher frequency. The influence of errors inside the DLL due to CMOS process on the performance of spur suppression is also analyzed in this work. Two independent calibration systems, continuous time calibration and switch capacitor integrator based calibration for DLL’s errors are presented, to reduce the delay errors. A spur reduction of 35 dB compared to a conventional structure is verified by the schematic simulation in Cadence.
A 2.4 GHz Phase Modulator for a WLAN OFDM Polar Transmitter in 0.18 um CMOS
(2014-09-11) Arbabi, Shokoufeh; Entesari, Kamran; Palermo, Samuel; Zoghi, Behbood; Khatri, Sunil
This research focuses on the design and implementation of a digital active phase modulator path of a polar transmitter in the case of orthogonal frequency division multiplex WLAN application. The phase modulation path of the polar transmitter provides a constant envelope phase modulated signal to the Power amplifier(PA) , operating in nonlinear high efficient switching mode. The core design of the phase modulator is based on linear vector-sum phase shifting topology to differential quadrature input signals. The active phase shifter consists of a DAC that generates binary weighted currents for I and Q branches and differential signed adder that vector-sums the generated quadrature currents to generate the phase at the output.6 bits control the phase shifter, creating 64 states with the resolution of 5:625° for the whole 360°. The linear (binary weighted) vector-sum technique generates a reduction in the resultant amplitude that should be taken into consideration in case of nonlinear PA in polar transmission. On the other hand, the digital phase information is applied as the control bits to the phase shifter that determine the weightings and the signs of the I and Q vectors. The key point is the operation of the phase modulator in terms of phase accuracy, with the wideband modulation standard such as OFDM WLAN. A technique has been proposed to enable the polar phase modulator to operate with a real-time wideband data and to compensate for the phase shifter output reduction. Since the reduction in gain is due to vector sum resultant of I and Q currents, it is compensated by modifying the I and Q currents for each 64 phase states. The design is implemented using 0.18 um CMOS technology and measured with maximum data rate of 64 QAM,OFDM modulation of WLAN standard. The output amplitude of the phase shifter with the correction technique is approximately constant over the 64 states with maximum variation of 3.5mv from the constant peak to peak value. The maximum achieved phase error is about 2° with a maximum DNL of 0.257.

Browse

Browsing Electronic Theses, Dissertations, and Records of Study (2002– ) by Title

Results Per Page

Sort Options