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Articles 1 - 21 of 21
Full-Text Articles in Physical Sciences and Mathematics
Exploring Run-Time Reduction In Programming Codes Via Query Optimization And Caching, Venkata Krishna Suhas Nerella
Exploring Run-Time Reduction In Programming Codes Via Query Optimization And Caching, Venkata Krishna Suhas Nerella
Doctoral Dissertations
"Object oriented programming languages raised the level of abstraction by supporting the explicit first class query constructs in the programming codes. These query constructs allow programmers to express operations on collections more abstractly than relying on their realization in loops or through provided libraries. Join optimization techniques from the field of database technology support efficient realizations of such language constructs. However, the problem associated with the existing techniques such as query optimization in Java Query Language (JQL) incurs run time overhead. Besides the programming languages supporting first-class query constructs, the usage of annotations has also increased in the software engineering …
Fundamental Properties Of Colloidal Unimolecular Polymer Particles, Minghang Chen
Fundamental Properties Of Colloidal Unimolecular Polymer Particles, Minghang Chen
Doctoral Dissertations
"Colloidal Unimolecular Polymer (CUP) particles are a new genre of material formed by self-assembly into spheroidal particles due to the effect of hydrophilic/hydrophobic interactions of the polymer with a change in the solvent. The particle sizes were characterized by means of Dynamic Light Scattering with corrected viscosities instead of water's viscosity. The distribution of particle size agreed well with the distribution of molecular weight proving that the polymer had undergone unimolecular collapse. The rheology study shows the presence of surface water and its significant effect on the rheology. The primary and secondary electroviscous effects were also found to play roles …
Isocyanate-Derived Organic Aerogels: Polyurethanes, Polyureas, Polyamides And Polyimides, Chakkaravarthy Chidambareswarapattar
Isocyanate-Derived Organic Aerogels: Polyurethanes, Polyureas, Polyamides And Polyimides, Chakkaravarthy Chidambareswarapattar
Doctoral Dissertations
"Aerogels are 3D assemblies of nanoparticles with high open porosity and high surface area, and are pursued for their low density, low thermal conductivity, low dielectric constant and high acoustic attenuation. The foundation for those exceptional properties is their complex hierarchical solid framework (agglomerates of porous, fractal secondary nanoparticles). On the down side, however, aerogels are also fragile materials. The mechanical strength of silica aerogels has been improved by crosslinking the framework with organic polymers. The crosslinking polymer has been assumed to form a conformal coating on the surface of the skeletal framework bridging covalently the elementary building blocks. However, …
Transport In Correlated And Uncorrelated Random Media, With Applications To Molecularly Doped Polymers, Nilanka Praveena Gurusinghe
Transport In Correlated And Uncorrelated Random Media, With Applications To Molecularly Doped Polymers, Nilanka Praveena Gurusinghe
Doctoral Dissertations
"The commonly observed Poole-Frenkel field dependence; of the mobility of photo-injected charges in molecularly-doped polymers has been shown to arise from the spatially-correlated, Gaussian energy distribution of transport sites encountered by charges moving through the material. Experimental current-time transients obtained for molecularly-doped polymers exhibit universality with respect to electric field and a metal-insulator-like transition from non-dispersive to dispersive transport, features usually identified with multiple trapping models that assume an uncorrelated exponential distribution of trap energies. For materials that exhibit both sets of features the possibility arises that both kinds of disorder coexist. We study here, analytically and numerically, transport in …
Characterization Of Nano-Scaled Metal-Hydrides Confined In Nano-Porous Carbon Frameworks, David Edward Peaslee
Characterization Of Nano-Scaled Metal-Hydrides Confined In Nano-Porous Carbon Frameworks, David Edward Peaslee
Doctoral Dissertations
"Metal hydrides are currently being studied to provide hydrogen for use in fuel cells and for transportation applications. Hydrogen can be stored in chemical compounds at higher density and lower volume than liquid H₂ or compressed gas. Thermodynamic properties of metal hydrides differ between bulk and nano-sized particles. Many metal hydrides with useful volumetric and gravimetric capacities have high decomposition temperatures, but when placed in nano-sized frameworks (or templates) desorption and adsorption temperatures can be fine-tuned to meet engineering requirements for real-world systems. Additionally, some metal hydrides have shown a change in the decomposition pathway when infiltrated into these frameworks, …
Social-Context Based Routing And Security In Delay Tolerant Networks, Roy A. Cabaniss
Social-Context Based Routing And Security In Delay Tolerant Networks, Roy A. Cabaniss
Doctoral Dissertations
"Delay Tolerant Networks (DTNs) were originally intended for interplanetary communications and have been applied to a series of difficult environments: wireless sensor networks, unmanned aerial vehicles, and short-range personal communications. There is a class of such environments in which nodes follow semi-predictable social patterns, such as wildlife tracking or personal devices. This work introduces a series of algorithms designed to identify the social patterns present in these environments and apply this data to difficult problems, such as efficient message routing and content distribution. Security is also difficult in a mobile environment. This is especially the case in the event that …
Quantum Phase Transitions In Disordered Magnets, David Nozadze
Quantum Phase Transitions In Disordered Magnets, David Nozadze
Doctoral Dissertations
"We study the effects of quenched weak disorder on quantum phase transitions in disordered magnets. The presence of disorder in the system can lead to a variety of exotic phenomena, e.g., the smearing of transitions or quantum Griffiths singularities. Phase transitions are smeared if individual spatial regions can order independently of the bulk system. In paper I, we study smeared quantum phase transitions in binary alloys A₁₋ₓBₓ that are tuned by changing the composition x. We show that in this case the ordered phase is extended over all compositions x < 1. We also study the composition dependence of observables. In paper II, we investigate the influence of spatial disorder correlations on smeared phase transitions. As an experimental example, we demonstrate in paper III, that the composition-driven ferromagnetic-toparamagnetic quantum phase transition in Sr₁₋ₓCaₓ RuO₃ is smeared. When individual spatial regions cannot order but fluctuate slowly, the phase transition is characterized by strong singularities in the quantum Griffiths phase. In paper IV, we develop a theory of the quantum Griffiths phases in disordered ferromagnetic metals. We show that the quantum Griffiths singularities are stronger than the usual power-law quantum Griffiths singularities in insulating magnets. In paper V, we present an efficient numerical method for studying quantum phase transitions in disordered systems with O(N) order parameter symmetry in the large-N limit. Our algorithm solves iteratively the large-N self-consistent equations for the renormalized distances from criticality. Paper VI is devoted to the study of transport properties in the quantum Griffiths phase associated with the antiferromagnetic quantum phase transition in a metal. We find unusual behavior of transport properties which is in contrast to the normal Fermi-liquid behavior"--Abstract, page v.
Polarization And Opinion Analysis In An Online Argumentation System For Collaborative Decision Support, Ravi Santosh Arvapally
Polarization And Opinion Analysis In An Online Argumentation System For Collaborative Decision Support, Ravi Santosh Arvapally
Doctoral Dissertations
"Argumentation is an important process in a collaborative decision making environment. Argumentation from a large number of stakeholders often produces a large argumentation tree. It is challenging to comprehend such an argumentation tree without intelligent analysis tools. Also, limited decision support is provided for its analysis by the existing argumentation systems. In an argumentation process, stakeholders tend to polarize on their opinions, and form polarization groups. Each group is usually led by a group leader. Polarization groups often overlap and a stakeholder is a member of multiple polarization groups. Identifying polarization groups and quantifying a stakeholder's degree of membership in …
Verification Of Information Flow Security In Cyber-Physical Systems, Rav Akella
Verification Of Information Flow Security In Cyber-Physical Systems, Rav Akella
Doctoral Dissertations
"With a growing number of real-world applications that are dependent on computation, securing the information space has become a challenge. The security of information in such applications is often jeopardized by software and hardware failures, intervention of human subjects such as attackers, incorrect design specification and implementation, other social and natural causes. Since these applications are very diverse, often cutting across disciplines a generic approach to detect and mitigate these issues is missing. This dissertation addresses the fundamental problem of verifying information security in a class of real world applications of computation, the Cyber-physical systems (CPSs). One of the motivations …
Structural And Magnetic Properties Of Ni And Cr Substituted La₀.₇Sr₀.₃Mno₃, Thomas Franklin Creel Jr.
Structural And Magnetic Properties Of Ni And Cr Substituted La₀.₇Sr₀.₃Mno₃, Thomas Franklin Creel Jr.
Doctoral Dissertations
"The La₁₋ₓSrₓMn1-yByO₃ perovskite systems where B represents a 3d transition metal such as Cr, Fe, Co, Ni, Cu, and Zn, are of significant interest due to their large magnetoresistance, and electronic transport properties that change significantly, depending on values of x and which transition metal used. Their applications in technology include cathodes for solid oxide fuel cells, resistance random access memory and catalysis. At certain doping concentrations on the B-site, metal-to-semiconductor or metal-to-insulator transitions coupled with colossal magnetoresistance occur, decreasing the resistivity (up to six orders of magnitude) upon the application of an external magnetic field. …
Creating New Superconducting & Semiconducting Nanomaterials And Investingating The Effect Of Reduced Dimensionality On Their Properties, Sukhada Mishra
Creating New Superconducting & Semiconducting Nanomaterials And Investingating The Effect Of Reduced Dimensionality On Their Properties, Sukhada Mishra
Doctoral Dissertations
"The field of nanomaterials has continued to attract researchers to understand the fundamentals and to investigate potential applications in the fields of semiconductor physics, microfabrication, nanomedicine, surface sciences etc. One of the most critical aspects of the nanomaterials research is to establish synthetic protocols, which can address the underlying product requirements of reproducibility, homogenous morphology and controlled elemental composition. We have focused our research in exploring synthetic routes for the synthesis of superconducting and semiconducting nanomaterials and analyze their structure--property relationship through detailed characterizations. The first part of dissertation is focused on the synthesis of superconducting FeSe nanostructures using catalyst …
Location Based Services In Wireless Ad Hoc Networks, Neelanjana Dutta
Location Based Services In Wireless Ad Hoc Networks, Neelanjana Dutta
Doctoral Dissertations
"In this dissertation, we investigate location based services in wireless ad hoc networks from four different aspects - i) location privacy in wireless sensor networks (privacy), ii) end-to-end secure communication in randomly deployed wireless sensor networks (security), iii) quality versus latency trade-off in content retrieval under ad hoc node mobility (performance) and iv) location clustering based Sybil attack detection in vehicular ad hoc networks (trust). The first contribution of this dissertation is in addressing location privacy in wireless sensor networks. We propose a non-cooperative sensor localization algorithm showing how an external entity can stealthily invade into the location privacy of …
Sparse Group Sufficient Dimension Reduction And Covariance Cumulative Slicing Estimation, Bilin Zeng
Sparse Group Sufficient Dimension Reduction And Covariance Cumulative Slicing Estimation, Bilin Zeng
Doctoral Dissertations
"This dissertation contains two main parts: In Part One, for regression problems with grouped covariates, we adopt the idea of sparse group lasso (Friedman et al., 2010) to the framework of the sufficient dimension reduction. We propose a method called the sparse group sufficient dimension reduction (sgSDR) to conduct group and within group variable selections simultaneously without assuming a specific model structure on the regression function. Simulation studies show that our method is comparable to the sparse group lasso under the regular linear model setting, and outperforms sparse group lasso with higher true positive rates and substantially lower false positive …
Palynology Of Acid-Saline Lakes Of Western Australiabiostratigraphy And Paleoenvironmental Reconstruction, Carlos A. Sanchez Botero
Palynology Of Acid-Saline Lakes Of Western Australiabiostratigraphy And Paleoenvironmental Reconstruction, Carlos A. Sanchez Botero
Doctoral Dissertations
"Lakes are excellent repositories of fossils and sedimentary features that provide clues to past climatic and geologic events. Sediments from four cores drilled in Lake Aerodrome (LA1-09, LA2-09) and Lake Brown (LB1-09, LB2-09), two of the hundreds of ephemeral lakes in southern Western Australia, were analyzed for their palynological contents to understand the geologic and climatic evolution of the depositional basin. Palynofacies assemblages defined by statistical analyses of dispersed organic matter suggested differences in the depositional conditions and probable correlations between Lake Aerodrome cores. Detailed identifications and quantification of organic-walled microfossils yielded two palynomorph assemblages that reflect a climatic turnover: …
Polybenzoxazine Aerogels: Synthesis, Characterization, Conversion To Porous Carbons, And Energetic Composites, Shruti Mahadik-Khanolkar
Polybenzoxazine Aerogels: Synthesis, Characterization, Conversion To Porous Carbons, And Energetic Composites, Shruti Mahadik-Khanolkar
Doctoral Dissertations
"Aerogels are nanoporous, low-density bulk objects, consisting of three-dimensional assemblies of nanoparticle. Structured similarly, polymeric aerogels are emerging as a mechanically strong alternative to traditional silica aerogels, which are fragile. Amongst polymeric aerogels, those based on polybenzoxazine (PBO - a type of phenolic resin), are extremely robust and comprise an economic alternative to resorcinol-formaldehyde aerogels, also a class of phenolic resins, as the main source of carbon aerogels. The drawback of the PBO chemistry has been the long (days) processing time at high-temperatures (>130 ºC). Herewith, we have developed an energy- and time-efficient process to PBO aerogels by inducing …
Privacy-Preserving Friend Recommendations In Online Social Networks, Bharath Kumar Samanthula
Privacy-Preserving Friend Recommendations In Online Social Networks, Bharath Kumar Samanthula
Doctoral Dissertations
"Online social networks, such as Facebook and Google+, have been emerging as a new communication service for users to stay in touch and share information with family members and friends over the Internet. Since the users are generating huge amounts of data on social network sites, an interesting question is how to mine this enormous amount of data to retrieve useful information. Along this direction, social network analysis has emerged as an important tool for many business intelligence applications such as identifying potential customers and promoting items based on their interests. In particular, since users are often interested to make …
Study Of Artificially Disordered Optical Fibers, Herath Mudiyanselage Sumudu Rasika Kumari Herath
Study Of Artificially Disordered Optical Fibers, Herath Mudiyanselage Sumudu Rasika Kumari Herath
Doctoral Dissertations
"Light transmission through photo-sensitive multi-mode fibers (MMF) with controlled volume disorder is investigated. Experiment shows that a segment of disordered MMF as short as 10 cm is sufficient to distribute power uniformly over all co-propagating modes and the intensity at the output surface of the fiber follows the Rayleigh negative exponential function. To explain the experimental findings, a comprehensive theoretical model is developed with three main results. First, statistical properties of all components of the dielectric tensor are obtained and analyzed in the framework a microscopical model of photo-sensitivity in a germano-silicate glasses. Secondly, it is shown that induced birefringence …
Geochemical And Isotopic Characterization Of Lead In Fugitive Dust From Unsurfaced Roads In Missouri, Emitt C. Witt
Geochemical And Isotopic Characterization Of Lead In Fugitive Dust From Unsurfaced Roads In Missouri, Emitt C. Witt
Doctoral Dissertations
"Eighteen unsurfaced roadways in Missouri's rural Ozark region were sampled to characterize the differences in trace element and isotopic chemistry to determine if there is a human health concern with inhaling and/or ingestion of fugitive dust generated by a moving vehicle. Road reaches were selected to represent those in similar rural areas with and without the presence of mining activity--13 roads were selected in the Viburnum Trend (VT) resource mining area and five were located to the southwest of the mining areas. Samples were collected using a novel cyclonic fugitive dust sampler (patent pending) that collects a composite sample from …
Optical Spectroscopic Studies Of Two Star Forming Regions, Kristen Leilani Erickson
Optical Spectroscopic Studies Of Two Star Forming Regions, Kristen Leilani Erickson
Doctoral Dissertations
"The ρ Ophiuchi and Serpens molecular clouds are sites of low mass star formation. The goals of this study were to identify young stellar objects (YSOs) and estimate ages and masses in order to infer an initial mass function (IMF), investigate disk evolution, and determine the star-forming history. Optical spectroscopic surveys of an unbiased sample of candidate young stars have been completed. Optical images taken in different photometric bands were used to create color-magnitude diagrams from which sources were selected for spectroscopic observation. In combination with published data, 135 association members in ρ Ophiuchi and 63 association members plus 16 …
Phase Transitions In Disordered Systems, Fawaz Y. Hrahsheh
Phase Transitions In Disordered Systems, Fawaz Y. Hrahsheh
Doctoral Dissertations
"Disorder can have a wide variety of consequences for the physics of phase transitions. Some transitions remain unchanged in the presence of disorder while others are completely destroyed. In this thesis we study the effects of disorder on several classical and quantum phase transitions in condensed matter systems. After a brief introduction, we study the ferromagnetic phase transition in a randomly layered Heisenberg magnet using large-scale Monte-Carlo simulations. Our results provide numerical evidence for the exotic infinite-randomness scenario. We study classical and quantum smeared phase transitions in substitutional alloys A₁₋ₓBₓ. Our results show that the disorder completely destroys the phase …
Quantum Phase Transitions In Impurity Models And Percolating Lattices, Manal M. Al-Ali
Quantum Phase Transitions In Impurity Models And Percolating Lattices, Manal M. Al-Ali
Doctoral Dissertations
"This thesis investigates the influence of random disorder and dissipation on zero-temperature quantum phase transitions. Both phenomena can fundamentally change the character of the phases of a quantum many-particle system and of the transitions between them. If dissipation and disorder occur simultaneously in a system undergoing a quantum phase transition, particularly strong effects can be expected. In the first paper reproduced in this thesis, we study a single quantum rotor coupled to a sub-Ohmic dissipative bath. We find that this system undergoes a quantum phase transition from a delocalized phase to a localized phase as the dissipation strength is increased. …