Theses and Dissertations
This collection includes both ASU Theses and Dissertations, submitted by graduate students, and the Barrett, Honors College theses submitted by undergraduate students.
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Description
The relationship between biodiversity and ecosystem functioning (BEF) is a central issue in ecology, and a number of recent field experimental studies have greatly improved our understanding of this relationship. Spatial heterogeneity is a ubiquitous characterization of ecosystem processes, and has played a significant role in shaping BEF relationships. The first step towards understanding the effects of spatial heterogeneity on the BEF relationships is to quantify spatial heterogeneity characteristics of key variables of biodiversity and ecosystem functioning, and identify the spatial relationships among these variables. The goal of our research was to address the following research questions based on data collected in 2005 (corresponding to the year when the initial site background information was conducted) and in 2008 (corresponding to the year when removal treatments were conducted) from the Inner Mongolia Grassland Removal Experiment (IMGRE) located in northern China: 1) What are the spatial patterns of soil nutrients, plant biodiversity, and aboveground biomass in a natural grassland community of Inner Mongolia, China? How are they related spatially? and 2) How do removal treatments affect the spatial patterns of soil nutrients, plant biodiversity, and aboveground biomass? Is there any change for their spatial correlations after removal treatments? Our results showed that variables of biodiversity and ecosystem functioning in the natural grassland community would present different spatial patterns, and they would be spatially correlated to each other closely. Removal treatments had a significant effect on spatial structures and spatial correlations of variables, compared to those prior to the removal treatments. The differences in spatial pattern of plant and soil variables and their correlations before and after the biodiversity manipulation may not imply that the results from BEF experiments like IMGRE are invalid. However, they do suggest that the possible effects of spatial heterogeneity on the BEF relationships should be critically evaluated in future studies.
ContributorsYuan, Fei (Author) / Wu, Jianguo (Thesis advisor) / Smith, Andrew T. (Committee member) / Rowe, Helen I (Committee member) / Arizona State University (Publisher)
Created2011
Description
Process variations have become increasingly important for scaled technologies starting at 45nm. The increased variations are primarily due to random dopant fluctuations, line-edge roughness and oxide thickness fluctuation. These variations greatly impact all aspects of circuit performance and pose a grand challenge to future robust IC design. To improve robustness, efficient methodology is required that considers effect of variations in the design flow. Analyzing timing variability of complex circuits with HSPICE simulations is very time consuming. This thesis proposes an analytical model to predict variability in CMOS circuits that is quick and accurate. There are several analytical models to estimate nominal delay performance but very little work has been done to accurately model delay variability. The proposed model is comprehensive and estimates nominal delay and variability as a function of transistor width, load capacitance and transition time. First, models are developed for library gates and the accuracy of the models is verified with HSPICE simulations for 45nm and 32nm technology nodes. The difference between predicted and simulated σ/μ for the library gates is less than 1%. Next, the accuracy of the model for nominal delay is verified for larger circuits including ISCAS'85 benchmark circuits. The model predicted results are within 4% error of HSPICE simulated results and take a small fraction of the time, for 45nm technology. Delay variability is analyzed for various paths and it is observed that non-critical paths can become critical because of Vth variation. Variability on shortest paths show that rate of hold violations increase enormously with increasing Vth variation.
ContributorsGummalla, Samatha (Author) / Chakrabarti, Chaitali (Thesis advisor) / Cao, Yu (Thesis advisor) / Bakkaloglu, Bertan (Committee member) / Arizona State University (Publisher)
Created2011
Description
Designing studies that use latent growth modeling to investigate change over time calls for optimal approaches for conducting power analysis for a priori determination of required sample size. This investigation (1) studied the impacts of variations in specified parameters, design features, and model misspecification in simulation-based power analyses and (2) compared power estimates across three common power analysis techniques: the Monte Carlo method; the Satorra-Saris method; and the method developed by MacCallum, Browne, and Cai (MBC). Choice of sample size, effect size, and slope variance parameters markedly influenced power estimates; however, level-1 error variance and number of repeated measures (3 vs. 6) when study length was held constant had little impact on resulting power. Under some conditions, having a moderate versus small effect size or using a sample size of 800 versus 200 increased power by approximately .40, and a slope variance of 10 versus 20 increased power by up to .24. Decreasing error variance from 100 to 50, however, increased power by no more than .09 and increasing measurement occasions from 3 to 6 increased power by no more than .04. Misspecification in level-1 error structure had little influence on power, whereas misspecifying the form of the growth model as linear rather than quadratic dramatically reduced power for detecting differences in slopes. Additionally, power estimates based on the Monte Carlo and Satorra-Saris techniques never differed by more than .03, even with small sample sizes, whereas power estimates for the MBC technique appeared quite discrepant from the other two techniques. Results suggest the choice between using the Satorra-Saris or Monte Carlo technique in a priori power analyses for slope differences in latent growth models is a matter of preference, although features such as missing data can only be considered within the Monte Carlo approach. Further, researchers conducting power analyses for slope differences in latent growth models should pay greatest attention to estimating slope difference, slope variance, and sample size. Arguments are also made for examining model-implied covariance matrices based on estimated parameters and graphic depictions of slope variance to help ensure parameter estimates are reasonable in a priori power analysis.
ContributorsVan Vleet, Bethany Lucía (Author) / Thompson, Marilyn S. (Thesis advisor) / Green, Samuel B. (Committee member) / Enders, Craig K. (Committee member) / Arizona State University (Publisher)
Created2011
Description
Due to the growing concerns on the depletion of petroleum based energy resources and climate change; fuel cell technologies have received much attention in recent years. Proton exchange membrane fuel cell (PEMFCs) features high energy conversion efficiency and nearly zero greenhouse gas emissions, because of its combination of the hydrogen oxidation reaction (HOR) at anode side and oxygen reduction reaction (ORR) at cathode side. Synthesis of Pt nanoparticles supported on multi walled carbon nanotubes (MWCNTs) possess a highly durable electrochemical surface area (ESA) and show good power output on proton exchange membrane (PEM) fuel cell performance. Platinum on multi-walled carbon nanotubes (MWCNTs) support were synthesized by two different processes to transfer PtCl62- from aqueous to organic phase. While the first method of Pt/MWCNTs synthesis involved dodecane thiol (DDT) and octadecane thiol (ODT) as anchoring agent, the second method used ammonium lauryl sulfate (ALS) as the dispersion/anchoring agent. The particle size and distribution of platinum were examined by high-resolution transmission electron microscope (HRTEM). The TEM images showed homogenous distribution and uniform particle size of platinum deposited on the surface of MWCNTs. The single cell fuel cell performance of the Pt/MWCNTs synthesized thiols and ALS based electrode containing 0.2 (anode) and 0.4 mg (cathode) Pt.cm-2 were evaluated using Nafion-212 electrolyte with H2 and O2 gases at 80 oC and ambient pressure. The catalyst synthesis with ALS is relatively simple compared to that with thiols and also showed higher performance (power density reaches about 1070 mW.cm-2). The Electrodes with Pt/MWCNTs nanocatalysts synthesized using ALS were characterized by cyclic voltammetry (CV) for durability evaluation using humidified H2 and N2 gases at room temperature (21 oC) along with commercial Pt/C for comparison. The ESA measured by cyclic voltammetry between 0.15 and 1.2 V showed significant less degradation after 1000 cycles for ALS based Pt/MWCNTs.
ContributorsLiu, Xuan (Author) / Madakannan, Arunachalanadar (Thesis advisor) / Munukutla, Lakshmi (Committee member) / Tamizhmani, Govindasamy (Committee member) / Arizona State University (Publisher)
Created2011
Description
Worldwide, riverine floodplains are among the most endangered landscapes. In response to anthropogenic impacts, riverine restoration projects are considerably increasing. However, there is a paucity of information on how riparian rehabilitation activities impact non-avian wildlife communities. I evaluated herpetofauna abundance, species richness, diversity (i.e., Shannon and Simpson indices), species-specific responses, and riparian microhabitat characteristics along three reaches (i.e., wildland, urban rehabilitated, and urban disturbed) of the Salt River, Arizona. The surrounding uplands of the two urbanized reaches were dominated by the built environment (i.e., Phoenix metropolitan area). I predicted that greater diversity of microhabitat and lower urbanization would promote herpetofauna abundance, richness, and diversity. In 2010, at each reach, I performed herpetofauna visual surveys five times along eight transects (n=24) spanning the riparian zone. I quantified twenty one microhabitat characteristics such as ground substrate, vegetative cover, woody debris, tree stem density, and plant species richness along each transect. Herpetofauna species richness was the greatest along the wildland reach, and the lowest along the urban disturbed reach. The wildland reach had the greatest diversity indices, and diversity indices of the two urban reaches were similar. Abundance of herpetofauna was approximately six times lower along the urban disturbed reach compared to the two other reaches, which had similar abundances. Principal Component Analysis (PCA) reduced microhabitat variables to five factors, and significant differences among reaches were detected. Vegetation structure complexity, vegetation species richness, as well as densities of Prosopis (mesquite), Salix (willow), Populus (cottonwood), and animal burrows had a positive correlation with at least one of the three herpetofauna community parameter quantified (i.e., herpetofauna abundance, species richness, and diversity indices), and had a positive correlation with at least one herpetofauna species. Overall, rehabilitation activities positively influenced herpetofauna abundance and species richness, whereas urbanization negatively influenced herpetofauna diversity indices. Based on herpetofauna/microhabitat correlations established, I developed recommendations regarding microhabitat features that should be created in order to promote herpetofauna when rehabilitating degraded riparian systems. Recommendations are to plant vegetation of different growth habit, provide woody debris, plant Populus, Salix, and Prosopis of various ages and sizes, and to promote small mammal abundance.
ContributorsBanville, Mélanie Josianne (Author) / Bateman, Heather L (Thesis advisor) / Brady, Ward (Committee member) / Stromberg, Juliet (Committee member) / Arizona State University (Publisher)
Created2011
Description
In this work, a new method, "Nanobonding" [1,2] is conceived and researched to bond Si-based surfaces, via nucleation and growth of a 2 D silicon oxide SiOxHx interphase connecting the surfaces at the nanoscale across macroscopic domains. Nanobonding cross-bridges two smooth surfaces put into mechanical contact in an O2/H2O mixed ambient below T <200 °C via arrays of SiOxHx molecules connecting into a continuous macroscopic bonding interphase. Nano-scale surface planarization via wet chemical processing and new spin technology are compared via Tapping Mode Atomic Force Microscopy (TMAFM) , before and after nano-bonding. Nanobonding uses precursor phases, 2D nano-films of beta-cristobalite (beta-c) SiO2, nucleated on Si(100) via the Herbots-Atluri (H-A) method [1]. beta-c SiO2 on Si(100) is ordered and flat with atomic terraces over 20 nm wide, well above 2 nm found in native oxides. When contacted with SiO2 this ultra-smooth nanophase can nucleate and grow domains with cross-bridging molecular strands of hydroxylated SiOx, instead of point contacts. The high density of molecular bonds across extended terraces forms a strong bond between Si-based substrates, nano- bonding [2] the Si and silica. A new model of beta-cristobalite SiO2 with its <110> axis aligned along Si[100] direction is simulated via ab-initio methods in a nano-bonded stack with beta-c SiO2 in contact with amorphous SiO2 (a-SiO2), modelling cross-bridging molecular bonds between beta-c SiO2 on Si(100) and a-SiO2 as during nanobonding. Computed total energies are compared with those found for Si(100) and a-SiO2 and show that the presence of two lattice cells of !-c SiO2 on Si(100) and a-SiO2 lowers energy when compared to Si(100)/ a-SiO2 Shadow cone calculations on three models of beta-c SiO2 on Si(100) are compared with Ion Beam Analysis of H-A processed Si(100). Total surface energy measurements via 3 liquid contact angle analysis of Si(100) after H-A method processing are also compared. By combining nanobonding experiments, TMAFM results, surface energy data, and ab-initio calculations, an atomistic model is derived and nanobonding is optimized. [1] US Patent 6,613,677 (9/2/03), 7,851,365 (12/14/10), [2] Patent Filed: 4/30/09, 10/1/2011
ContributorsWhaley, Shawn D (Author) / Culbertson, Robert J. (Thesis advisor) / Herbots, Nicole (Committee member) / Rez, Peter (Committee member) / Marzke, Robert F (Committee member) / Lindsay, Stuart (Committee member) / Chamberlin, Ralph V (Committee member) / Arizona State University (Publisher)
Created2011
Description
This thesis describes several experiments based on carbon nanotube nanofludic devices and field-effect transistors. The first experiment detected ion and molecule translocation through one single-walled carbon nanotube (SWCNT) that spans a barrier between two fluid reservoirs. The electrical ionic current is measured. Translocation of small single stranded DNA oligomers is marked by large transient increases in current through the tube and confirmed by a PCR (polymerase chain reaction) analysis. Carbon nanotubes simplify the construction of nanopores, permit new types of electrical measurement, and open new avenues for control of DNA translocation. The second experiment constructed devices in which the interior of a single-walled carbon nanotube field-effect transistor (CNT-FET) acts as a nanofluidic channel that connects two fluid reservoirs, permitting measurement of the electronic properties of the SWCNT as it is wetted by an analyte. Wetting of the inside of the SWCNT by water turns the transistor on, while wetting of the outside has little effect. This finding may provide a new method to investigate water behavior at nanoscale. This also opens a new avenue for building sensors in which the SWCNT functions as an electronic detector. This thesis also presents some experiments that related to nanofabrication, such as construction of FET with tin sulfide (SnS) quantum ribbon. This work demonstrates the application of solution processed IV-VI semiconductor nanostructures in nanoscale devices.
ContributorsCao, Zhai (Author) / Lindsay, Stuart (Thesis advisor) / Vaiana, Sara (Committee member) / Ros, Robert (Committee member) / Marzke, Robert (Committee member) / Shumway, John (Committee member) / Arizona State University (Publisher)
Created2011
Description
Many nanotechnology-related principles can be demonstrated in a way that is understandable for elementary school-aged children through at-home activity videos. As a part of a National Science Foundation funded grant, Dr. Qing Hua Wang’s research group at Arizona State University developed a nanotechnology-related activity website, Nano@Home, for students. In conjunction with ASU’s virtual Open Door 2021, this creative project aimed to create activity videos based on the Nano@Home website to make the activities more interactive for students.
ContributorsOliver, Ruth Kaylyn (Author) / Wang, Qing Hua (Thesis director) / Krause, Stephen (Committee member) / Materials Science and Engineering Program (Contributor, Contributor) / Watts College of Public Service & Community Solut (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
This thesis was conducted to study and analyze the fund allocation process adopted by different states in the United States to reduce the impact of the Covid-19 virus. Seven different states and their funding methodologies were compared against the case count within the state. The study also focused on development of a physical distancing index based on three significant attributes. This index was then compared to the expenditure and case counts to support decision making.
A regression model was developed to analyze and compare how different states case counts played out against the regression model and the risk index.
ContributorsJaisinghani, Shaurya (Author) / Mirchandani, Pitu (Thesis director) / Clough, Michael (Committee member) / McCarville, Daniel R. (Committee member) / Industrial, Systems & Operations Engineering Prgm (Contributor) / Department of Information Systems (Contributor) / Industrial, Systems & Operations Engineering Prgm (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
Dreadnought is a free-to-play multiplayer flight simulation in which two teams of 8 players each compete against one another to complete an objective. Each player controls a large-scale spaceship, various aspects of which can be customized to improve a player’s performance in a game. One such aspect is Officer Briefings, which are passive abilities that grant ships additional capabilities. Two of these Briefings, known as Retaliator and Get My Good Side, have strong synergy when used together, which has led to the Dreadnought community’s claiming that the Briefings are too powerful and should be rebalanced to be more in line with the power levels of other Briefings. This study collected gameplay data with and without the use of these specific Officer Briefings to determine the precise impact on gameplay. Linear correlation matrices and inference on two means were used to determine performance impact. It was found that, although these Officer Briefings do improve an individual player’s performance in a game, they do not have a consistent impact on the player’s team performance, and that these Officer Briefings are therefore not in need of rebalancing.
ContributorsJacobs, Max I. (Author) / Schneider, Laurence (Thesis director) / Tran, Samantha (Committee member) / Mechanical and Aerospace Engineering Program (Contributor) / School of Mathematical and Statistical Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05