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Articles 31 - 60 of 187
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Variable Selection In Competing Risks Using The L1-Penalized Cox Model, Xiangrong Kong
Variable Selection In Competing Risks Using The L1-Penalized Cox Model, Xiangrong Kong
Theses and Dissertations
One situation in survival analysis is that the failure of an individual can happen because of one of multiple distinct causes. Survival data generated in this scenario are commonly referred to as competing risks data. One of the major tasks, when examining survival data, is to assess the dependence of survival time on explanatory variables. In competing risks, as with ordinary univariate survival data, there may be explanatory variables associated with the risks raised from the different causes being studied. The same variable might have different degrees of influence on the risks due to different causes. Given a set of …
Closed-Loop Adaptive Optics Control In Strong Atmospheric Turbulence, Todd M. Venema
Closed-Loop Adaptive Optics Control In Strong Atmospheric Turbulence, Todd M. Venema
Theses and Dissertations
A self-referencing interferometer based closed-loop adaptive optics controller is developed which is designed to operate effectively under strong turbulence conditions. The aberrated optical field is modeled stochastically and then estimates of the state of the system are developed using a steady-state, fixed-gain Kalman filter. The phase of the optical field is considered the state of the system which is wrapped in a limited range of (-π, π]. This phase is unwrapped through the use of a least-squares reconstructor which has been modified to work effectively in the presence of branch points associated with strong turbulence. The conjugate of the optical …
Electronic State Distributions Of Y Ba2Cu3O7-X Laser Ablated Plumes, Patrick D. Kee
Electronic State Distributions Of Y Ba2Cu3O7-X Laser Ablated Plumes, Patrick D. Kee
Theses and Dissertations
The application of spectral and imagery diagnostics to YBa2Cu3O7 (YBCO) laser-ablated plumes was systematically studied to determine their effectiveness for process control. Emission signatures were collected for plumes created by ablating bulk YBCO with a pulsed laser source. A KrF (λ=248 nm) laser source operating at 4-10 J/cm2 at a 4-10 Hz pulse repetition frequency was used to ablate a bulk YBCO target at O2 background pressures ranging from 50 to 400 mTorr. Emission spectra were collected over the 500 to 860 nm bandpass at distances from the target ranging from 31.4 to …
A Study Of The Irradiance-And-Temperature-Dependence Of Mid-Wave-Infrared (Mwir)Absorption In Indium Antimonide (Insb), John M. Callahan
A Study Of The Irradiance-And-Temperature-Dependence Of Mid-Wave-Infrared (Mwir)Absorption In Indium Antimonide (Insb), John M. Callahan
Theses and Dissertations
This work entails further investigation of the absorption of photons in indium antimonide (InSb). Previously work at the Air Force Institute of Technology (AFIT) attributed laser blooming effects in InSb focal plane arrays (FPA’s) to the Burstein-Moss effect. The contributing effect is from a decrease in the absorption of the InSb material, such that the transmitted optical energy scatters off the integrated circuitry beneath the InSb thin film back into the optical system. To evaluate this, irradiance-dependent laser-absorption experiments were performed on thinned, InSb wafers prior to their FPA fabrication. The samples were illuminated with a focused CO2 laser at …
A Confidence Paradigm For Classification Systems, Nathan J. Leap
A Confidence Paradigm For Classification Systems, Nathan J. Leap
Theses and Dissertations
There is no universally accepted methodology to determine how much confidence one should have in a classifier output. This research proposes a framework to determine the level of confidence in an indication from a classifier system where the output is or can be transformed into a posterior probability estimate. This is a theoretical framework that attempts to unite the viewpoints of the classification system developer (or engineer) and the classification system user (or war-fighter). The paradigm is based on the assumptions that the system confidence acts like, or can be modeled as a value and that indication confidence can be …
The Roc Curves Of Fused Independent Classification Systems, Michael B. Walsh
The Roc Curves Of Fused Independent Classification Systems, Michael B. Walsh
Theses and Dissertations
The need for optimal target detection arises in many different fields. Due to the complexity of many targets, it is thought that the combination of multiple classification systems, which can be tuned to several individual target attributes or features, might lead to more optimal target detection performance. The ROC curves of fused independent two-label classification systems may be generated by the mathematical combination of their ROC curves to achieve optimal classifier performance without the need to test every Boolean combination. The monotonic combination of two-label independent classification systems which assign labels to the same target types results in a lattice …
Using Simulation Optimization To Construct Efficient Screening Strategies For Cervical Cancer, Christodoulos Foufoulides
Using Simulation Optimization To Construct Efficient Screening Strategies For Cervical Cancer, Christodoulos Foufoulides
Theses and Dissertations
Cervical cancer is the second most common type of cancer in women worldwide. Because cervical cancer is usually asymptomatic until the disease is in its advanced stages, cervical screening is of central importance towards combating cervical cancer. Alternative screening strategies are evaluated from an economic point of view through cost-effectiveness analysis. In the literature however, studies perform cost-effectiveness analysis on a limited number of de facto or predetermined screening policies. At present, no attempt has been made to construct efficient screening strategies through optimization, before cost-effectiveness analysis is applied. In this study simulation optimization is used to construct efficient screening …
Testing Direct Simulation Monte Carlo Methods Against The Fluid Equations In The Inductively Coupled Plasma Mass Spectrometer, William R. Somers
Testing Direct Simulation Monte Carlo Methods Against The Fluid Equations In The Inductively Coupled Plasma Mass Spectrometer, William R. Somers
Theses and Dissertations
A Direct Simulation Monte Carlo fluid dynamics code named FENIX has been employed to study gas flow-through properties of the inductively coupled plasma mass spectrometer (ICP-MS). Simulation data have been tested against the Navier-Stokes and heat equations in order to see if FENIX functions properly. The Navier-Stokes and heat equations have been constructed from simulation data and are compared term by term. This comparison shows that FENIX is able to correctly reproduce fluid dynamics throughout the ICP-MS simulation, with an exception immediately behind the ICP-MS sampler cone, where the continuum criterion for the Navier-Stokes equation is not met. Testing the …
Biologically Relevant Multiple Sequence Alignment, Hyrum D. Carroll
Biologically Relevant Multiple Sequence Alignment, Hyrum D. Carroll
Theses and Dissertations
Researchers use multiple sequence alignment algorithms to detect conserved regions in genetic sequences and to identify drug docking sites for drug development. In this dissertation, a novel algorithm is presented for using physicochemical properties to increase the accuracy of multiple sequence alignments. Secondary structures are also incorporated in the evaluation function. Additionally, the location of the secondary structures is assimilated into the function. Multiple properties are combined with weights, determined from prediction accuracies of protein secondary structures using artificial neural networks. A new metric, the PPD Score is developed, that captures the average change in physicochemical properties. Using the physicochemical …
Implementation Of Optical Spectra Calculations In Fireball: A Local-Orbital Density Functional Theory Approach, Ivan Grigoryevich Okhrimenko
Implementation Of Optical Spectra Calculations In Fireball: A Local-Orbital Density Functional Theory Approach, Ivan Grigoryevich Okhrimenko
Theses and Dissertations
We have expanded the capabilities of the ab initio tight-binding molecular dynamics package FIREBALL to include calculations of optical properties. Basic zero order approximation is based on transitions between Kohn-Sham states. Corrections for electron-electron interactions are based on time dependant density functional theory (TDDFT). Consistent with the FIREBALL approach, we use precalculated integrals and approximations to make the program faster.
On Graph Isomorphism And The Pagerank Algorithm, Christopher J. Augeri
On Graph Isomorphism And The Pagerank Algorithm, Christopher J. Augeri
Theses and Dissertations
A graph is a key construct for expressing relationships among objects, such as the radio connectivity between nodes contained in an unmanned vehicle swarm. The study of such networks may include ranking nodes based on importance, for example, by applying the PageRank algorithm used in some search engines to order their query responses. The PageRank values correspond to a unique eigenvector typically computed by applying the power method, an iterative technique based on matrix multiplication. The first new result described herein is a lower bound on the execution time of the PageRank algorithm that is derived by applying standard assumptions …
Stimulated Brillouin Scattering Phase Conjugation In Fiber Optic Waveguides, Steven M. Massey
Stimulated Brillouin Scattering Phase Conjugation In Fiber Optic Waveguides, Steven M. Massey
Theses and Dissertations
The objective of this research effort was to demonstrate the path to continuous wave, coherent beam combination through stimulated Brillouin scattering phase conjugation in optical fiber. This work experimentally determined the fiber parameters necessary for phase conjugation in step-index optical fiber. Continuous wave phase conjugation using stimulated Brillouin scattering in step-index fibers was achieved for the first time with a fidelity of 0.8 and a threshold power of 16 W in a 15-m fiber with 0.13 NA. A fidelity of 0.8 was also achieved using 40 m of fiber with 0.06-NA and a threshold power of 15 W. The fidelity …
I. Thermodynamics And Magnetism Of Cu2ocl2 Ii. Repairs To Microcalorimeter The "2"S Are Subscripts, And The Second 2 Is Preceded By A Lower Case L, Not A One, Thomas J. Parry
Theses and Dissertations
Adiabatic calorimetry provides accurate and precise specific heat (Cp) data. From this data, thermodynamic functions may be calculated. Cu2OCl2, melanothallite, became of interest as part of a study of a particular thermochemical cycle. The experimental specific heat data and the calculated thermodynamic functions are reported here. Free energies of formation, calculated from the thermodynamic functions, suggest the particular cycle of interest with this compound as an intermediate is not feasible; uncertainty as to the accuracy of CuO and CuCl2 data used in the calculations indicate further study may be necessary. Upon collection of the specific heat data, an antiferromagnetic transition …
An Infrastructure For Performance Measurement And Comparison Of Information Retrieval Solutions, Gary Saunders
An Infrastructure For Performance Measurement And Comparison Of Information Retrieval Solutions, Gary Saunders
Theses and Dissertations
The amount of information available on both public and private networks continues to grow at a phenomenal rate. This information is contained within a wide variety of objects, including documents, e-mail archives, medical records, manuals, pictures and music. To be of any value, this data must be easily searchable and accessible. Information Retrieval (IR) is concerned with the ability to find and gain access to relevant information. As electronic data repositories continue to proliferate, so too, grows the variety of methods used to locate and access the information contained therein. Similarly, the introduction of innovative retrieval strategies—and the optimization of …
Generalized Random Walks, Their Trees, And The Transformation Method Of Option Pricing, Thomas Gordon Stewart
Generalized Random Walks, Their Trees, And The Transformation Method Of Option Pricing, Thomas Gordon Stewart
Theses and Dissertations
The random walk is a powerful model. Chemistry, Physics, and Finance are just a few of the disciplines that model with the random walk. It is clear from its varied uses that despite its simplicity, the simple random walk it very flexible. There is one major drawback, however, to the simple random walk and the geometric random walk. The limiting distribution is either normal, lognormal, or a levy process with infinite variance. This thesis introduces an new random walk aimed at overcoming this drawback. Because the simple random walk and the geometric random walk are special cases of the proposed …
Autonomous And Intelligent Radio Switching, Quiyi Duan
Autonomous And Intelligent Radio Switching, Quiyi Duan
Theses and Dissertations
With the proliferation of mobile applications and the abundance of wireless devices, it is increasingly common for devices to support multiple radios. When two devices are communicating they should choose the best available radio based on user preference and application requirements. This type of “radio switching” should happen automatically, so that the system optimizes performance dynamically. To achieve this objective, we design an Autonomous and Intelligent Radio Switching (AIRS) system to leverage the radio heterogeneity common in today's wireless devices. The AIRS system consists of three key components. First, we design a radio preference evaluation module to dynamically select the …
Multi-Class Classification For Identifying Jpeg Steganography Embedding Methods, Benjamin M. Rodriguez Ii
Multi-Class Classification For Identifying Jpeg Steganography Embedding Methods, Benjamin M. Rodriguez Ii
Theses and Dissertations
Over 725 steganography tools are available over the Internet, each providing a method for covert transmission of secret messages. This research presents four steganalysis advancements that result in an algorithm that identifies the steganalysis tool used to embed a secret message in a JPEG image file. The algorithm includes feature generation, feature preprocessing, multi-class classification and classifier fusion. The first contribution is a new feature generation method which is based on the decomposition of discrete cosine transform (DCT) coefficients used in the JPEG image encoder. The generated features are better suited to identifying discrepancies in each area of the decomposed …
A Radical Conjugate Addition Approach To The Total Synthesis Of Celogentin C, Steven G. Capps
A Radical Conjugate Addition Approach To The Total Synthesis Of Celogentin C, Steven G. Capps
Theses and Dissertations
The synthesis of five chiral DBFOX (dibenzofuran-oxazoline) ligands with either aryl or benzyl substituents will be presented. The requisite amino alcohols were obtained with high enantioselectivity either commercially (DBFOX/Bn), via Sharpless asymmetric aminohydroxylation (DBFOX/Nap, DBFOX/t-BuPh, DBFOX/Pip), or via phase-transfer catalyzed asymmetric alkylation (DBFOX/MeNap). These ligands, complexed with Mg(NTf2)2, were used as Lewis acid promoters of enantioselective radical conjugate additions to α/β-unsaturated nitro-amides/esters. A summary of these results is presented and discussed. These findings led us to believe that our initial binding model between metal, ligand, and substrate was flawed. Thus, we figured that if we started with a functionality known …
A Microanalytical Approach To Understanding The Origin Of Cumulate Xenoliths From Mauna Kea, Hawaii, Megan Pickard
A Microanalytical Approach To Understanding The Origin Of Cumulate Xenoliths From Mauna Kea, Hawaii, Megan Pickard
Theses and Dissertations
Cumulate xenoliths erupted with alkalic hawaiite lavas from a postshield cinder cone on Mauna Kea, Hawaii include a variety of mafic and ultramafic rock types. Previous studies of major and trace element compositions of minerals in the xenoliths are interpreted to show transitional to alkalic magma parentages from the postshield stage, although any orthopyroxene-bearing xenoliths are considered to have tholeiitic parents. Major element compositions minerals were analyzed using the electron microprobe and trace element compositions of clinopyroxene grains were analyzed by laser ablation inductively coupled plasma mass spectrometry. In this study, major element compositions of clinopyroxene, olivine and plagioclase grains …
Magmatic Sulfur And Chlorine Abundances At Stromboli, Italy And Their Role In The Formation Of Vesicle-Hosted Metal Alloys, Nichelle Lynn Baxter
Magmatic Sulfur And Chlorine Abundances At Stromboli, Italy And Their Role In The Formation Of Vesicle-Hosted Metal Alloys, Nichelle Lynn Baxter
Theses and Dissertations
Strand et al. (2002) discovered small metal alloy grains rich in Cu, Co, and Sn (maximum size 150 µm) in vesicles of lava from Kilauea Volcano. These alloys are also found in basaltic rocks of several Italian volcanoes. To better understand the origin of these metal-rich grains, bombs from Stromboli Volcano were examined. Two bomb types were collected from Stromboli: pumiceous bombs and scoriaceous bombs. Bulk rock trace element geochemistry indicates that there are no significant differences in Cu, Co, or Sn (the three major components of the metal alloys) between the pumiceous and scoriaceous bombs. Comparison of olivine melt …
On Autonomous Multi-Agent Control In Wilderness Search And Rescue: A Mixed Initiative Approach, Benjamin C. Hardin
On Autonomous Multi-Agent Control In Wilderness Search And Rescue: A Mixed Initiative Approach, Benjamin C. Hardin
Theses and Dissertations
Searching for lost people in a Wilderness Search and Rescue (WiSAR) scenario is a task that can benefit from large numbers of agents, some of whom may be robotic. These agents may have differing levels of autonomy, determined by the set of tasks they are performing. In addition, the level of autonomy that results in the best performance may change due to varying workload or other factors. Allowing a supervisor and a searcher to jointly decide the correct level of autonomy for a given situation (“mixed initiative”) results in better overall performance than giving an agent absolute control over their …
Pre-Eruptive Conditions Of The Oligocene Wah Wah Springs Tuff, Southeastern Great Basin Ignimbrite Province, Kurtus Steven Woolf
Pre-Eruptive Conditions Of The Oligocene Wah Wah Springs Tuff, Southeastern Great Basin Ignimbrite Province, Kurtus Steven Woolf
Theses and Dissertations
The Wah Wah Springs Tuff (30.0 Ma) is one of several very large volume ash-flow tuffs (>3200 km³ of erupted magma) that were emplaced near the peak of the flare-up of activity in the Great Basin ignimbrite province of western North America. It can be characterized as a "monotonous intermediate" ignimbrite because of its intermediate concentrations of silica (~63 to ~70 wt. %), apparent uniform chemical and mineralogical characteristics, and crystal-rich nature (32 ± 10 % phenocrysts on a dense rock basis). The major phase assemblage found throughout deposit is similar to other monotonous intermediates with a few exceptions …
Regulators Of G-Protein Signaling, Rgs13 And Rgs16, Are Associated With Cxcl12-Mediated Cd4+ T Cell Migration, Lijin Xia
Theses and Dissertations
Chemokines are important chemical signals that guide lymphocyte movement within the immune system and promote the organization and functions of germinal centers (GCs) in the secondary lymphoid tissues. Previous studies have shown that GC T cells exhibit high expression of chemokine receptor 4, CXCR4, but that these cells are unable to migrate to the ligand for this receptor, the chemokine CXCL12. This “migratory paralysis” to CXCL12 was found to be correlated with the expression of two Regulators of G-protein Signaling, RGS13 and RGS16 in the GC T cells. The objective of my research was to determine whether RGS13 and RGS16 …
Spectroscopic Study Of Compressible Mobile Phase And Stationary Phase Behavior In Chromatography, Lawrence R. Baker
Spectroscopic Study Of Compressible Mobile Phase And Stationary Phase Behavior In Chromatography, Lawrence R. Baker
Theses and Dissertations
Raman spectroscopy, laser-induced fluorescence, and sum-frequency generation (SFG) spectroscopy are used to investigate the behavior of compressible mobile phases and stationary phases under a variety of chromatographic conditions. Efforts to understand and optimize separations employing compressible mobile phases have been limited by a lack of understanding of the mobile phase density gradient. Mobile phase compressibility leads to gradients in linear velocity and solute retention and affects separation speed and efficiency, especially in packed columns. This work describes on-column density measurement of CO2, a common carrier fluid for SFC and SGC, in packed capillary columns using Raman microspectroscopy. On-column detection by …
Theory And Estimation Of Acoustic Intensity And Energy Density, Derek C. Thomas
Theory And Estimation Of Acoustic Intensity And Energy Density, Derek C. Thomas
Theses and Dissertations
In order to facilitate the acquisition and accurate interpretation of intensity and energy density data in high-amplitude pressure fields, the expressions for intensity and energy density are examined to ascertain the impact of nonlinear processes on the standard expressions. Measurement techniques for estimating acoustic particle velocity are presented. The finite-difference method is developed in an alternate manner and presented along with bias and confidence estimates. Additionally, two new methods for estimating the local particle velocity are presented. These methods appears to eliminate the errors and bias associated with the finite-difference technique for certain cases.
Assessing Multivariate Heritability Through Nonparametric Methods, Benjamin Alan Carper
Assessing Multivariate Heritability Through Nonparametric Methods, Benjamin Alan Carper
Theses and Dissertations
The similarities between generations of living subjects are often quantified by heritability. By distinguishing genotypic variation, or variation due to parental pairings, from phenotypic variation, or normal intraspecies variation, the heritability of traits can be estimated. Due to the multivariate nature of many traits, such as size and shape, computation of heritability can be difficult. Also, assessment of the variation of the heritability estimate is extremely difficult. This study uses nonparametric methods, namely the randomization test and the bootstrap, to obtain both a measure of the extremity of the observed heritability and an assessment of the uncertainty.
Lyapunov Exponents And Invariant Manifold For Random Dynamical Systems In A Banach Space, Zeng Lian
Lyapunov Exponents And Invariant Manifold For Random Dynamical Systems In A Banach Space, Zeng Lian
Theses and Dissertations
We study the Lyapunov exponents and their associated invariant subspaces for infinite dimensional random dynamical systems in a Banach space, which are generated by, for example, stochastic or random partial differential equations. We prove a multiplicative ergodic theorem. Then, we use this theorem to establish the stable and unstable manifold theorem for nonuniformly hyperbolic random invariant sets.
The Tropical Jacobian Of A Tropical Elliptic Curve Is S^1(Q), Darryl Gene Wade
The Tropical Jacobian Of A Tropical Elliptic Curve Is S^1(Q), Darryl Gene Wade
Theses and Dissertations
We establish consistent definitions for divisors, principal divisors, and Jacobians of a tropical elliptic curve and show that for a tropical elliptic cubic C , the associated Jacobian (or zero divisor class group) is the group S^1(Q).
Simple, Secure, Selective Delegation In Online Identify Systems, Bryant Gordon Cutler
Simple, Secure, Selective Delegation In Online Identify Systems, Bryant Gordon Cutler
Theses and Dissertations
The ability to delegate privileges to others is so important to users of online identity systems that users create ad hoc delegation systems by sharing authentication credentials if no other easy delegation mechanism is available. With the rise of internet-scale relationship-based single sign-on protocols like OpenID, the security risks of password sharing are unacceptable. We therefore propose SimpleAuth, a simple modification to relationship-based authentication protocols that gives users a secure way to selectively delegate subsets of their privileges, making identity systems more flexible and increasing user security. We also present a proof-of-concept implementation of the SimpleAuth pattern using the sSRP …
Predicting The Longevity Of Dvdr Media By Periodic Analysis Of Parity, Jitter, And Ecc Performance Parameters, Daniel Patrick Wells
Predicting The Longevity Of Dvdr Media By Periodic Analysis Of Parity, Jitter, And Ecc Performance Parameters, Daniel Patrick Wells
Theses and Dissertations
For the last ten years, DVD-R media have played an important role in the storage of large amounts of digital data throughout the world. During this time it was assumed that the DVD-R was as long-lasting and stable as its predecessor, the CD-R. Several reports have surfaced over the last few years questioning the DVD-R's ability to maintain many of its claims regarding archival quality life spans. These reports have shown a wide range of longevity between the different brands. While some DVD-Rs may last a while, others may result in an early and unexpected failure. Compounding this problem is …