Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Keyword
-
- Algorithm (3)
- Database (2)
- MOLECULES (2)
- ANALOGS (1)
- ANIONS (1)
-
- APPROXIMATION (1)
- ATOMS (1)
- AUGMENTED-WAVE METHOD; SIMPLE METAL-CLUSTERS; BIMETALLIC CLUSTERS; GOLD CLUSTERS; CHEMISTRY; PSEUDOPOTENTIALS; ABUNDANCES; STABILITY; MOLECULES; CATIONS (1)
- Agency (1)
- Agile Manifesto (1)
- AlN (1)
- Algorithm evaluation (1)
- Algorithmic modeling (1)
- Aluminum iodide (1)
- ArcGIS (1)
- Astronomy (1)
- Astrophysics (1)
- Atomic cluster (1)
- Axis (1)
- BASIS-SETS (1)
- BENZENE MOLECULES (1)
- Bacteria (1)
- Bald eagle (1)
- Bandit problem (1)
- Body mass (1)
- Buchberger's Algorithm (1)
- CASCADE LASERS; MU-M; WAVELENGTH RANGE; BAND-OFFSET; INP; TEMPERATURE; TRANSITION; OPERATION (1)
- COATED IRON NANOPARTICLES; GOLD; CLUSTERS; ENERGY; 1ST-PRINCIPLES; BEHAVIOR; OXYGEN; FIELD (1)
- COMPLEXES (1)
- COMPUTER-SIMULATIONS (1)
- Publication Type
Articles 31 - 48 of 48
Full-Text Articles in Physical Sciences and Mathematics
Determination Of The Band Gap Bowing Parameter Of A1xga1-Xn With Contactless Electroreflectance, Laura C. Mcglinchey
Determination Of The Band Gap Bowing Parameter Of A1xga1-Xn With Contactless Electroreflectance, Laura C. Mcglinchey
Theses and Dissertations
Contactless electroreflectance (CER), a modulation spectroscopy (MS) technique, has been used to study the A and C exciton transitions in A1xGa1-xN layers for a composition range of 0 ≤ x ≤ 0.48 at room temperature. Taking the entire composition range (0 ≤ x ≤ 1) into account by incorporating a previously reported band gap energy for AlN, the dependence of the A-exciton transition on composition showed a downward bowing from linearity. A bowing parameter of b = 1.7 eV was found. Analysis of the lower composition range 0 ≤ x ≤ 0.48 resulted in a linear fit, as did the …
A Comparison For Longitudinal Data Missing Due To Truncation, Rong Liu
A Comparison For Longitudinal Data Missing Due To Truncation, Rong Liu
Theses and Dissertations
Many longitudinal clinical studies suffer from patient dropout. Often the dropout is nonignorable and the missing mechanism needs to be incorporated in the analysis. The methods handling missing data make various assumptions about the missing mechanism, and their utility in practice depends on whether these assumptions apply in a specific application. Ramakrishnan and Wang (2005) proposed a method (MDT) to handle nonignorable missing data, where missing is due to the observations exceeding an unobserved threshold. Assuming that the observations arise from a truncated normal distribution, they suggested an EM algorithm to simplify the estimation.In this dissertation the EM algorithm is …
A Model To Predict 24-Hour Urinary Creatinine Level Using Repeated Measurements, Donna S. Kroos
A Model To Predict 24-Hour Urinary Creatinine Level Using Repeated Measurements, Donna S. Kroos
Theses and Dissertations
Creatinine is a metabolic waste product, removed from the blood by the kidneys, and excreted in the urine. The measurement of creatinine is used in the assessment and monitoring of many medical conditions as well as in the determination or adjustment of absorbed dosage of pesticides. Earlier models to predict 24-hour urinary creatinine used ordinary least squares regression and assumed that the subjects' observations were uncorrelated. However, many of these studies had repeated creatinine measurements for each of their subjects. Repeated measures on the same subject frequently are correlated. Using data from the NIOSH-CDC "Pesticide Dose Monitoring in Turf Applicators" …
A Normal-Mixture Model With Random-Effects For Rr-Interval Data, Jessica Mckinney Ketchum
A Normal-Mixture Model With Random-Effects For Rr-Interval Data, Jessica Mckinney Ketchum
Theses and Dissertations
In many applications of random-effects models to longitudinal data, such as heart rate variability (HRV) data, a normal-mixture distribution seems to be more appropriate than the normal distribution assumption. While the random-effects methodology is well developed for several distributions in the exponential family, the case of the normal-mixture has not been dealt with adequately in the literature. The models and the estimation methods that have been proposed in the past assume the conditional model (fixing the random-effects) to be normal and allow a mixture distribution for the random effects (Xu and Hedeker, 2001, Xu, 1995). The methods proposed in this …
Quantifying The Effects Of Correlated Covariates On Variable Importance Estimates From Random Forests, Ryan Vincent Kimes
Quantifying The Effects Of Correlated Covariates On Variable Importance Estimates From Random Forests, Ryan Vincent Kimes
Theses and Dissertations
Recent advances in computing technology have lead to the development of algorithmic modeling techniques. These methods can be used to analyze data which are difficult to analyze using traditional statistical models. This study examined the effectiveness of variable importance estimates from the random forest algorithm in identifying the true predictor among a large number of candidate predictors. A simulation study was conducted using twenty different levels of association among the independent variables and seven different levels of association between the true predictor and the response. We conclude that the random forest method is an effective classification tool when the goals …
Enhancing The Third-Order Nonlinear Optical Properties Of Porphyrins And Molecular Wires, Jonathan L. Humphrey
Enhancing The Third-Order Nonlinear Optical Properties Of Porphyrins And Molecular Wires, Jonathan L. Humphrey
Theses and Dissertations
The third-order nonlinear optical (NLO) properties of indium tin oxide (ITO) thin films, Fe3+, Mn3+, Co2+ 5,10,15,20-tetrakis-4hydroxytetraphenyl)porphyrin (TPP) films, and a series of ethynyl-linked azobenzene oligomers were investigated using degenerate four wave mixing (DFWM) with 100 fs laser pulses. To measure the NLO of ITO thin films, A DFWM method for measuring thin films on thick substrates was refined for the characterization of films less than 100 nm thick and applied to ITO films ~25 nm thick. It was found that the third-order nonlinear susceptibility of ITO, χ(3)ITO, is purely electronic at 900 - 1300 nm (11000 - 7700 cm-1) …
Approaching The Singularity In Gowdy Universes, Bartlett Douglas Edmonds Jr.
Approaching The Singularity In Gowdy Universes, Bartlett Douglas Edmonds Jr.
Theses and Dissertations
It has been shown that the cosmic censorship conjecture holds for polarized Gowdy spacetimes. In the more general, unpolarized case, however, the question remains open. It is known that cylindrically symmetric dust can collapse to form a naked singularity. Since Gowdy universes comprise gravitational waves that are locally cylindrically symmetric, perhaps these waves can collapse onto a symmetry axis and create a naked singularity. It is known that in the case of cylindrical symmetry, event horizons will not form under gravitational collapse, so the formation of a singularity on the symmetry axis would be a violation of the cosmic censorship …
Isolation Of Legionella Pneumophila From Well-Maintained Emergency Showers And Eyewash Stations, Jessica Mae Myers
Isolation Of Legionella Pneumophila From Well-Maintained Emergency Showers And Eyewash Stations, Jessica Mae Myers
Theses and Dissertations
Legionella pneumophila is a gram-negative bacterium responsible for Legionnaire's disease, and is commonly transmitted via aerosolized water. Legionella colonization of emergency eyewash and shower stations may pose an exposure hazard to users of these stations. There is little information about the role of these stations as significant reservoirs for Legionella. Samples were collected from 67 stations in an industrial facility. At the time of this study, the stations within this facility were under a routine maintenance program that included at least monthly flushing. This study also included the analysis for other bacterial organisms to determine an association between the presence …
Photochemical Applications To The Study Of Complexity Phospholipid Bilayer Environments, Christopher John Wohl Jr.
Photochemical Applications To The Study Of Complexity Phospholipid Bilayer Environments, Christopher John Wohl Jr.
Theses and Dissertations
The physical and biophysical properties of a biological membrane model, phosphatidylcholine bilayers, were investigated using novel spiropyran/merocyanine molecular probes. The femtosecond to second dynamics of this system's photochemistry enabled bilayer viscosity and free volume to be studied over a broad time scale. Spiropyrans/merocyanines with different polarity were synthesized by changing the substitution of the indole moiety enabling determination of the trans-membrane properties of the bilayer. In addition, transient grating spectroscopy was used to study thermal energy transfer in phospholipid bilayers on a picosecond time scale.Femtosecond transient absorption spectroscopy was used to study the photo-induced spiropyran ring-opening and isomerization reactions that …
Statistical Methods And Experimental Design For Inference Regarding Dose And/Or Interaction Thresholds Along A Fixed-Ratio Ray, Sharon Dziuba Yeatts
Statistical Methods And Experimental Design For Inference Regarding Dose And/Or Interaction Thresholds Along A Fixed-Ratio Ray, Sharon Dziuba Yeatts
Theses and Dissertations
An alternative to the full factorial design, the ray design is appropriate for investigating a mixture of c chemicals, which are present according to a fixed mixing ratio, called the mixture ray. Using single chemical and mixture ray data, we can investigate interaction among the chemicals in a particular mixture. Statistical models have been used to describe the dose-response relationship of the single agents and the mixture; additivity is tested through the significance of model parameters associated with the coincidence of the additivity and mixture models.It is often assumed that a chemical or mixture must be administered above an unknown …
Cowboy: An Agile Programming Methodology For A Solo Programmer, Ashby Brooks Hollar
Cowboy: An Agile Programming Methodology For A Solo Programmer, Ashby Brooks Hollar
Theses and Dissertations
Very little research in software engineering has focused on the model of a programmer working alone. These so-called cowboys are disdained for not working in teams to build software. In reality many cowboys work by themselves due to the circumstances of their work environment, not because they are unable or unwilling to work with well with others. These solo programmers could benefit from a methodology to assist them in consistently developing reliable software on time and within budget while satisfying the customer's needs. Cowboy was designed to help fill this void. This agile-based system incorporates the benefits of agile methodologies …
Electronic Counting Rules For The Stability Of Metal-Silicon Clusters, J. Ulises Reveles, Shiv N. Khanna
Electronic Counting Rules For The Stability Of Metal-Silicon Clusters, J. Ulises Reveles, Shiv N. Khanna
Physics Publications
First principles electronic structure calculations have been carried out to examine the stability of cationic, neutral, and anionic MSi15, MSi16, and MSi17 (M=Sc, Ti, and V) clusters. ScSi16−, TiSi16, and VSi16+ are found to be particularly stable in agreement with recent experiments. It is shown that the enhanced stability can be reconciled within a model where each Si atom coordinated to the metal contributes one electron to the valence pool. Clusters where the total number of valence electrons obtained by summing one electron from each Si site coordinated to metal atom and the valence electrons of the metal attain 20 …
Ferromagnetism In Al1−Xcrxn Thin Films By Density Functional Calculations, Q. Wang, A. K. Kandalam, Q. Sun, Puru Jena
Ferromagnetism In Al1−Xcrxn Thin Films By Density Functional Calculations, Q. Wang, A. K. Kandalam, Q. Sun, Puru Jena
Physics Publications
We report the results of a theoretical study of magnetic coupling between Cr atoms doped in bulk AlN as well as AlN (112¯0) thin films having wurtzite structure. The calculations are based on density fuctional theory with the generalized gradient approximation to the exchange and correlation potential. In the thin film, modeled by a slab of finite thickness, Cr atoms are found to cluster around N on the surface layer and couple ferromagnetically. The results for the Cr-doped AlN crystal are similar, namely, Cr atoms cluster around N and couple ferromagnetically. In the thin film, the preference of Cr to …
Bayesian Analysis, Endogenous Data,And Convergence Of Beliefs, Andrew T. Foerster
Bayesian Analysis, Endogenous Data,And Convergence Of Beliefs, Andrew T. Foerster
Theses and Dissertations
Problems in statistical analysis, economics, and many other disciplines often involve a trade-off between rewards and additional information that could yield higher future rewards. This thesis investigates such a trade-off, using a class of problems known as bandit problems. In these problems, a reward-seeking agent makes decisions based upon his beliefs about a parameter that controls rewards. While some choices may generate higher short-term rewards, other choices may provide information that allows the agent to learn about the parameter, thereby potentially increasing future rewards. Learning occurs if the agent's subjective beliefs about the parameter converge over time to the parameter's …
Design And Analysis Methods For Cluster Randomized Trials With Pair-Matching On Baseline Outcome: Reduction Of Treatment Effect Variance, Misook Park
Theses and Dissertations
Cluster randomized trials (CRT) are comparative studies designed to evaluate interventions where the unit of analysis and randomization is the cluster but the unit of observation is individuals within clusters. Typically such designs involve a limited number of clusters and thus the variation between clusters is left uncontrolled. Experimental designs and analysis strategies that minimize this variance are required. In this work we focus on the CRT with pre-post intervention measures. By incorporating the baseline measure into the analysis, we can effectively reduce the variance of the treatment effect. Well known methods such as adjustment for baseline as a covariate …
Quantitative Model For The Prediction Of Hydrodynamic Size Of Nonionic Reverse Micelles, Melissa A. Michaels
Quantitative Model For The Prediction Of Hydrodynamic Size Of Nonionic Reverse Micelles, Melissa A. Michaels
Theses and Dissertations
The sizes of nonionic reverse micelles were investigated as a function of the molecular structure of the surfactant, the type of oil, the total concentration of surfactant [NP], the ratio of NP4 to total surfactant (r), the water to surfactant molar ratio (ω), temperature, salt concentration, and polar phase. The basis of our investigation was nonylphenol polyethoxylates - NP4 and NP7. Micelle sizes were determined using dynamic light scattering (DLS). A central composite experimental design was used to quantitatively model reverse micelle size as a function of ω, [NP], and r. The model has demonstrated the capability of predicting the …
Assessing, Modifying, And Combining Data Fields From The Virginia Office Of The Chief Medical Examiner (Ocme) Dataset And The Virginia Department Of Forensic Science (Dfs) Datasets In Order To Compare Concentrations Of Selected Drugs, Amy Elizabeth Herrin
Theses and Dissertations
The Medical Examiner of Virginia (ME) dataset and the Virginia Department of Forensic Science Driving Under the Influence of Drugs (DUI) datasets were used to determine whether people have the potential to develop tolerances to diphenhydramine, cocaine, oxycodone, hydrocodone, methadone, and morphine. These datasets included the years 2000-2004 and were used to compare the concentrations of these six drugs between people who died from a drug-related cause of death (of the drug of interest) and people who were pulled over for driving under the influence. Three drug pattern groups were created to divide each of the six drug-specific datasets in …
A Prelude To A Third Dimension Of The Periodic Table: Superatoms Of Aluminum Iodide Clusters, Naiche Owen Jones
A Prelude To A Third Dimension Of The Periodic Table: Superatoms Of Aluminum Iodide Clusters, Naiche Owen Jones
Theses and Dissertations
Calculations have been carried out to investigate the stability and electronic structure of aluminum iodide clusters using first principles gradient-corrected density functional theory. Analysis of A113Ix-, A114Ix-, and A17I- clusters reveals that their stability is governed by the geometrically unperturbed A113-, A1142+, and A17+ units, respectively, that are demonstrated to constitute the compact cores of the clusters upon significant iodine content. The compact, icosahedral A113, icosahedral-like A1 14, and capped square bi-pyramid A17 superatom structures of the stable aluminum cores have an analogous electronic configuration to that of halogen, alkaline-earth, and alkaline atoms, respectively. Novel chemistry is demonstrated in superatoms, …