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Articles 1 - 30 of 200
Full-Text Articles in Engineering
Characterization Of Wireless Communications Networks Using Machine Learning And 3d Electromagnetic Wave Propagation Simulations, Margaret Mary Rooney
Characterization Of Wireless Communications Networks Using Machine Learning And 3d Electromagnetic Wave Propagation Simulations, Margaret Mary Rooney
Dissertations, Theses, and Masters Projects
In this work, we employ machine learning, signal identification, and signal classification to infer network processes governing packet transmission in dense, non-cooperative wireless networks. We exploit signal features in radio frequency (RF) transmissions to generate fingerprints that can enable the characterization of transmission events in a non-cooperative cognitive radio network or in a cognitive adaptive electronic attack scenario. In these situations, we have anticipated a need to depend heavily on identifying RF features that correspond to the way in which devices access spectrum channels and to the interactions of transmitted signals with the devices' surroundings. We develop improved signal processing …
Growth And Properties Of Vapor Diffused Nb3sn Coating For Superconducting Radiofrequency Accelerator Cavity Applications, Uttar Last Pudasaini
Growth And Properties Of Vapor Diffused Nb3sn Coating For Superconducting Radiofrequency Accelerator Cavity Applications, Uttar Last Pudasaini
Dissertations, Theses, and Masters Projects
The desire to reduce construction and operating costs of future SRF accelerators motivates the search for higher-performing alternative materials. Nb3Sn (Tc ~ 18.3 K and Hsh ~ 425 mT) is the front runner. The tin vapor diffusion process is currently the technique of choice to produce promising Nb3Sn-coated cavities. Understanding Nb3Sn nucleation and growth in this process is essential to progress. Samples representing different stages of Nb3Sn formation have been produced and studied to elucidate the effects of nucleation, growth, process conditions, and impurities. Nb3Sn films with thickness …
Boron Nitride Nanotubes (Bnnts) For Thermal Management And Structural Reinforcement, Mahmoud Samy Mohamed Fahmy Amin
Boron Nitride Nanotubes (Bnnts) For Thermal Management And Structural Reinforcement, Mahmoud Samy Mohamed Fahmy Amin
Dissertations, Theses, and Masters Projects
Boron nitride nanotubes (BNNTs) are a fascinating material that has a lot of potential applications due to its outstanding physical and chemical properties. BNNTs synthesized using different high- and low-temperature methods, unfortunately, contain 30-70% impurities. To maximize the potential of BNNTs, new characterization techniques and purification methods are needed, especially with respect to industrial applications. Research groups have used different characterization techniques to monitor the synthesis and purity of BNNTs. Quantitative and qualitative characterization of the tubes for quality or purity control has not been previously described in the literature. In this work, we created a comprehensive set of thermogravimetric …
Nanofibrils As The Basic Building Blocks Of Spider Silk, Qijue Wang
Nanofibrils As The Basic Building Blocks Of Spider Silk, Qijue Wang
Dissertations, Theses, and Masters Projects
Spider silk is a natural high-performance biopolymer with superior mechanical properties, resulting from its hierarchical structure. With protein nanofibrils observed in various spider and silkworm silks, the critical role of nanofibrils in achieving the silk's mechanical behavior has been widely suggested by both experimental observations and numerical simulations. However, a close review of available evidence of silk nanofibrils reveals many crucial aspects are still largely ambiguous or unknown. This further hinders the development of advanced silk-based materials. The simple structure of the ribbon-like recluse (Loxosceles) silk provides an ideal opportunity to investigate silk nanofibrils. By studying the surface and internal …
Additive Manufacturing Of Nanomaterial Based Hierarchical Structures, John Michael Gardner
Additive Manufacturing Of Nanomaterial Based Hierarchical Structures, John Michael Gardner
Dissertations, Theses, and Masters Projects
Aerospace systems demand high performance materials that minimize weight while functioning under extreme environmental conditions. One way to meet these requirements is by incorporating hierarchical structures into part design. These structures are known to impart unique mechanical properties not characteristic of the bulk material such as high strength and toughness. It is difficult, however, to manufacture these structures due to the inherent trade-off between part size and feature resolution in traditional manufacturing processes. Additive manufacturing offers a potential solution to these issues by allowing material placement directly at desired locations. This loosens geometric constraints and allows for multiple contiguous materials …
Optical Characterization Of Dynamic Exchange Coupling Interaction In Ferromagnetic Heterostructures, Xiao Liu
Optical Characterization Of Dynamic Exchange Coupling Interaction In Ferromagnetic Heterostructures, Xiao Liu
Dissertations, Theses, and Masters Projects
This thesis presents the optical characterization of interfacial exchange coupling interaction in ferromagnetic bilayer heterostructures. Both static and dynamic magnetic response are investigated in the exchange-coupled Co2FeAl/(Ga,Mn)As bilayer system using static magneto-optical Kerr effect (MOKE) and time-resolved magneto optical Kerr effect (TRMOKE) techniques. The goal of this thesis is to understand the underlying physics of the interfacial exchange coupling effect on the ultrafast spin dynamics in a ferromagnetic metal/ferromagnetic semiconductor bilayer heterostructure. Our finding provides a viable pathway for designing advanced semiconductor spintronic devices for ultrafast low-power spin manipulation. First, a significant enhancement of the excitation efficiency of coherent magnetization …
Security Enhancements In Voice Over Ip Networks, Seyed Amir Iranmanesh
Security Enhancements In Voice Over Ip Networks, Seyed Amir Iranmanesh
Dissertations, Theses, and Masters Projects
Voice delivery over IP networks including VoIP (Voice over IP) and VoLTE (Voice over LTE) are emerging as the alternatives to the conventional public telephony networks. With the growing number of subscribers and the global integration of 4/5G by operations, VoIP/VoLTE as the only option for voice delivery becomes an attractive target to be abused and exploited by malicious attackers. This dissertation aims to address some of the security challenges in VoIP/VoLTE. When we examine the past events to identify trends and changes in attacking strategies, we find that spam calls, caller-ID spoofing, and DoS attacks are the most imminent …
Surface Modification Of Synthetic And Natural Polymers Using Deep Uv (172 Nm) Irradiation, Lopamudra Das
Surface Modification Of Synthetic And Natural Polymers Using Deep Uv (172 Nm) Irradiation, Lopamudra Das
Dissertations, Theses, and Masters Projects
The ability to modify the surfaces of polymers and impart desirable functionalities without affecting the bulk-mediated physical properties is vital for advanced materials development. Photochemical approaches to surface modification are particularly attractive as they minimize the need for use of hazardous materials used in conventional wet chemical technologies, and are relatively faster, efficient and convenient to use. In this research, we undertook a combined experimental and computational approach to understand the effect of deep UV irradiation on a broad range of polymeric materials, and develop a scalable and deployable surface modification strategy that could be extended to all. Four polyesters, …
Surfactant Free Emulsion Polymerization Of Poly(Styrene-Co-Methyl Methacrylate): Correlation Of Microsphere Characteristics With Monomer Reactivity And Water Solubility, Samantha Applin
Dissertations, Theses, and Masters Projects
Polymeric microspheres have been used in a broad range of applications from chromatographic separation techniques to analysis of air flow over aerodynamic surfaces. The preparation of microspheres from many polymer families has consequently been extensively studied using a variety of synthetic approaches. Although there are a myriad of polymeric microsphere synthesis methods, free-radical initiated emulsion polymerization is one of the most common techniques. In this work, poly(styrene-co-methyl methacrylate) microspheres were synthesized via surfactant-free emulsion polymerization. The effects of the co-monomer composition and addition time on particle size distribution, particle formation, and particle morphology were investigated. Particles were characterized using dynamic …
Vertically Oriented Graphene Electric Double Layer Capacitors, Dilshan V. Premathilake
Vertically Oriented Graphene Electric Double Layer Capacitors, Dilshan V. Premathilake
Dissertations, Theses, and Masters Projects
Vertically oriented graphene nanosheets (VOGN) synthesized by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) have been fabricated as electrical double layer capacitors (EDLCs). The relatively open morphology of the films provided good frequency response, but had limited capacitance compared to present day activated carbon EDLCs. The objective of this research was to improve the capacitance of these films to a commercially viable level while maintaining sufficient frequency response for AC filtering. The growth of VOGN on Ni and Al substrates has been studied in this work. The native oxide on Ni was thinned at temperatures above ~600ºC with the …
The Thin Ribbon Silk Of The Brown Recluse Spider: Structure, Mechanical Behavior, And Biomimicry, Sean Robert Koebley
The Thin Ribbon Silk Of The Brown Recluse Spider: Structure, Mechanical Behavior, And Biomimicry, Sean Robert Koebley
Dissertations, Theses, and Masters Projects
Silk has enormous potential as a next-generation material: it is a biopolymer spun from protein at ambient temperature and pressure, and the best spider silks are as strong as steel and tougher than Kevlar. Because of its green production, mechanical robustness, and biocompatibility, silk has been researched for use in a range of engineering and biomedical applications. However, despite exciting recent advances in artificial silk fabrication via recombinant techniques, reserachers remain unable to fully replicate the complex assembly and hierarchical structure of native silks. Herein, we describe our morphological and mechanical characterization of a uniquely simple model silk system that …
Modeling Flocculation And Deflocculation Processes Of Cohesive Sediments, Xiaoteng Shen
Modeling Flocculation And Deflocculation Processes Of Cohesive Sediments, Xiaoteng Shen
Dissertations, Theses, and Masters Projects
The transport and fate of cohesive sediments are responsible for many engineering, environmental, economic and policy issues that relate to, for example, siltation and dredging in navigation channels, water quality, water turbidity, pollutant transports, and biological ecosystem responses. Our current understanding, however, is insufficient to conduct accurate quantitative predictions of these processes. This is because the cohesive particles in natural waters will flocculate, which determines the settling, and thus the deposition behaviors. The simulation of flocculation processes is a primary challenge since the time variation of Floc Size Distribution (FSD) is controlled by a partial differential equation that also contains …
Assessing The Impact Of Climate Change On Proposed Restoration Of The Lynnhaven River Ecosystem, Emily E. Skeehan
Assessing The Impact Of Climate Change On Proposed Restoration Of The Lynnhaven River Ecosystem, Emily E. Skeehan
Dissertations, Theses, and Masters Projects
Environmental degradation of the Chesapeake Bay (CB) and its sub-estuaries has been linked to population growth in the surrounding coastal zone, rapid development in the watershed and resultant nutrient loading into the Bay. Consequently, the federal government and its partners have developed restoration plans to mitigate the effects of eutrophication and improve essential ecosystem functions, though few restoration plans have considered the interactive effects of climate change. Climate change and other anthropogenic drivers are causing changes in ecosystem structure and function, thereby impacting the beneficial services ecosystems provide. While some studies have attempted to quantitatively predict the benefits of ecosystem …
Development Of Boron-Containing Polyimide Materials And Poly(Arylene Ether)S For Radiation Shielding, Brittani May Collins
Development Of Boron-Containing Polyimide Materials And Poly(Arylene Ether)S For Radiation Shielding, Brittani May Collins
Dissertations, Theses, and Masters Projects
No abstract provided.
Canary Red: Preserving Cochineal And Contrasting Colonial Histories On Lanzarote, Sarah Mattes
Canary Red: Preserving Cochineal And Contrasting Colonial Histories On Lanzarote, Sarah Mattes
Dissertations, Theses, and Masters Projects
No abstract provided.
The Technique Of The Poquoson-Style Log Canoe, David Andrews Moran
The Technique Of The Poquoson-Style Log Canoe, David Andrews Moran
Dissertations, Theses, and Masters Projects
No abstract provided.
Magneto-Optics And Magneto-Transport Studies On Thin Films For Sensor Applications, Kaida Yang
Magneto-Optics And Magneto-Transport Studies On Thin Films For Sensor Applications, Kaida Yang
Dissertations, Theses, and Masters Projects
Recent progress and interest have bought considerable effort to bear on the synthesis and opportunities of magnetic thin films in different fields. There are applications in many fields, including remote sensing, waveguide applications, hard drive applications, etc. at the College of William and Mary, we have focused on utilizing magnetic thin films in some of these applications and are deeply involved in the optimization process of the thin films.
Superconducting Thin Films For Srf Cavity Applications: A Route To Higher Field Gradient Linacs, Wiliam Michael Roach
Superconducting Thin Films For Srf Cavity Applications: A Route To Higher Field Gradient Linacs, Wiliam Michael Roach
Dissertations, Theses, and Masters Projects
Many linear accelerator (linac) applications rely on the use of superconducting radio frequency (SRF) cavities. In order to overcome the current field gradient limits imposed by the use of bulk niobium, a model involving the deposition of alternating superconducting-insulating-superconducting (SIS) thin films onto the interior surface of SRF cavities has been proposed. Since SRF performance is a surface phenomenon, the critical surface of these cavities is less than 1 micron thick, thus enabling the use of thin films. Before such approach can successfully be implemented fundamental studies correlating the microstructure and superconducting properties of thin films are needed. to this …
Effective Resource And Workload Management In Data Centers, Lei Lu
Effective Resource And Workload Management In Data Centers, Lei Lu
Dissertations, Theses, and Masters Projects
The increasing demand for storage, computation, and business continuity has driven the growth of data centers. Managing data centers efficiently is a difficult task because of the wide variety of datacenter applications, their ever-changing intensities, and the fact that application performance targets may differ widely. Server virtualization has been a game-changing technology for IT, providing the possibility to support multiple virtual machines (VMs) simultaneously. This dissertation focuses on how virtualization technologies can be utilized to develop new tools for maintaining high resource utilization, for achieving high application performance, and for reducing the cost of data center management.;For multi-tiered applications, bursty …
An Evaluation Of A Reduced Bar Spacing Turtle Excluder Device In The U.S Gulf Of Mexico Offshore Shrimp Trawl Fishery, Michel Anthony Nalovic
An Evaluation Of A Reduced Bar Spacing Turtle Excluder Device In The U.S Gulf Of Mexico Offshore Shrimp Trawl Fishery, Michel Anthony Nalovic
Dissertations, Theses, and Masters Projects
Shrimp are the most economically valuable internationally-traded seafood commodity, and wild-caught, trawled shrimp make up almost half of the ~6.6 million metric tons of annual global production. Shrimp trawling is responsible for one-third of the world’s total fisheries bycatch, leading many to consider shrimp trawling to be the single most destructive fishing practice in the world. Though the bycatch of large marine animals can be significantly reduced by use of turtle excluder devices (TEDs) on shrimp trawls, current TED designs are ineffective at reducing the capture of smaller organisms which represent a large portion of the total bycatch. To further …
Nonlinear Optical Studies Of Photoelastic Effect And Magneto-Plasmonics, Wei Zheng
Nonlinear Optical Studies Of Photoelastic Effect And Magneto-Plasmonics, Wei Zheng
Dissertations, Theses, and Masters Projects
Nonlinear optical (NLO) processes are optical phenomena involving a nonlinear response to an applied light field. Two kinds of nonlinearities are studied in this dissertation: magnetic-induced second-harmonic generation (MSHG) interacting with surface plasmon, called "nonlinear magnetoplasmonics" (NMP), and the nonlinear index induced by a strong pump beam in Titanium doped sapphire crystal, referred to as population-induced nonlinear index effect.;The fundamentals of the major effects involved are discussed, which include: surface plasmon and its field enhancement effect, MSHG technique and phenomenological calculations, the contrast ratio of magnetic switching, the calculation of lensing effects, population induced strain, and photoelastic effect. Furthermore, the …
Use Of Pattern Classification Algorithms To Interpret Passive And Active Data Streams From A Walking-Speed Robotic Sensor Platform, Eric Allen Dieckman
Use Of Pattern Classification Algorithms To Interpret Passive And Active Data Streams From A Walking-Speed Robotic Sensor Platform, Eric Allen Dieckman
Dissertations, Theses, and Masters Projects
In order to perform useful tasks for us, robots must have the ability to notice, recognize, and respond to objects and events in their environment. This requires the acquisition and synthesis of information from a variety of sensors. Here we investigate the performance of a number of sensor modalities in an unstructured outdoor environment, including the Microsoft Kinect, thermal infrared camera, and coffee can radar. Special attention is given to acoustic echolocation measurements of approaching vehicles, where an acoustic parametric array propagates an audible signal to the oncoming target and the Kinect microphone array records the reflected backscattered signal. Although …
Optical Characterization Of Magnetism In Magnetic/Nonmagnetic Heterostructures, Yichun Fan
Optical Characterization Of Magnetism In Magnetic/Nonmagnetic Heterostructures, Yichun Fan
Dissertations, Theses, and Masters Projects
This thesis focuses on the study of the static and dynamic magnetic interactions in ferromagnetic/nonmagnetic heterostructures using interface-specific and time-resolved optical techniques. The goal of this thesis is to elucidate the interface exchange coupling, magnetic anisotropy, and coherent spin dynamics in these advanced material systems, crucial to the realization of high performance spintronic devices.;First, a pronounced exchange bias (EB) phenomenon is observed in Fe/MgO (001) by magnetic second harmonic generation. The bulk magnetization does not, in marked contrast to typical systems where EB is manifested only in the net magnetization. The magnitude of the exchange bias varies with interface oxygen …
High-Performance Nanocomposites Designed For Radiation Shielding In Space And An Application Of Gis For Analyzing Nanopowder Dispersion In Polymer Matrixes, Joseph Simcha Auslander
High-Performance Nanocomposites Designed For Radiation Shielding In Space And An Application Of Gis For Analyzing Nanopowder Dispersion In Polymer Matrixes, Joseph Simcha Auslander
Dissertations, Theses, and Masters Projects
No abstract provided.
Polymeric Radiation Shielding For Applications In Space: Polyimide Synthesis And Modeling Of Multi-Layered Polymeric Shields, Clinton Cleveland Schiavone
Polymeric Radiation Shielding For Applications In Space: Polyimide Synthesis And Modeling Of Multi-Layered Polymeric Shields, Clinton Cleveland Schiavone
Dissertations, Theses, and Masters Projects
No abstract provided.
The Malleability Of Spatial Ability Under Treatment Of A First Lego League-Based Robotics Unit, Steven Vincent Coxon
The Malleability Of Spatial Ability Under Treatment Of A First Lego League-Based Robotics Unit, Steven Vincent Coxon
Dissertations, Theses, and Masters Projects
No abstract provided.
Surface Impedance Of Superconducting Radio Frequency (Srf) Materials, Binping Xiao
Surface Impedance Of Superconducting Radio Frequency (Srf) Materials, Binping Xiao
Dissertations, Theses, and Masters Projects
Superconducting radio frequency (SRF) technology is widely adopted in particle accelerators. There remain many open questions, however, in developing a systematic understanding of the fundamental behavior of SRF materials, including niobium treated in different ways and various other bulk/thin film materials that are fabricated with different methods under assorted conditions. A facility that can measure the SRF properties of small samples in a range of 2∼40 K temperature is needed in order to fully answer these questions. The Jefferson Lab surface impedance characterization (SIC) system has been designed to attempt to meet this requirement. It consists of a sapphire-loaded cylindrical …
An Input Centric Paradigm For Program Dynamic Optimizations And Lifetime Evolvement, Kai Tian
An Input Centric Paradigm For Program Dynamic Optimizations And Lifetime Evolvement, Kai Tian
Dissertations, Theses, and Masters Projects
Accurately predicting program behaviors (e.g., memory locality, method calling frequency) is fundamental for program optimizations and runtime adaptations. Despite decades of remarkable progress, prior studies have not systematically exploited the use of program inputs, a deciding factor of program behaviors, to help in program dynamic optimizations. Triggered by the strong and predictive correlations between program inputs and program behaviors that recent studies have uncovered, the dissertation work aims to bring program inputs into the focus of program behavior analysis and program dynamic optimization, cultivating a new paradigm named input-centric program behavior analysis and dynamic optimization.;The new optimization paradigm consists of …
Enhanced Field Emission From Vertically Oriented Graphene By Thin Solid Film Coatings, Michael Bagge-Hansen
Enhanced Field Emission From Vertically Oriented Graphene By Thin Solid Film Coatings, Michael Bagge-Hansen
Dissertations, Theses, and Masters Projects
Recent progress and a coordinated national research program have brought considerable effort to bear on the synthesis and application of carbon nanostructures for field emission. at the College of William and Mary, we have developed field emission arrays of vertically oriented graphene (carbon nanosheets, CNS) that have demonstrated promising cathode performance, delivering emission current densities up to 2 mA/mm2 and cathode lifetime > 800 hours. The work function ( & phis;) of CNS and other carbonaceous cathode materials has been reported to be &phis;∼4.5-5.1 eV. The application of low work function thin films can achieve several orders of magnitude enhancement of …
First-Principles Calculations Of Nuclear Magnetic Resonance Chemical Shielding Tensors In Complex Ferroelectric Perovskites, Daniel Lawrence Pechkis
First-Principles Calculations Of Nuclear Magnetic Resonance Chemical Shielding Tensors In Complex Ferroelectric Perovskites, Daniel Lawrence Pechkis
Dissertations, Theses, and Masters Projects
Nuclear magnetic resonance (NMR) spectroscopy is one of the most important experimental probes of local atomistic structure, chemical ordering, and dynamics. Recently, NMR has increasingly been used to study complex ferroelectric perovskite alloys, where spectra can be difficult to interpret. First-principles calculations of NMR spectra can greatly assist in this task. In this work, oxygen, titanium, and niobium NMR chemical shielding tensors, s&d4; , were calculated with first-principles methods for ferroelectric transition metal prototypical ABO3 perovskites [SrTiO3, BaTiO 3, PbTiO3 and PbZrO3] and A(B,B')O3 perovskite alloys Pb(Zr1/2Ti1/2)O3 (PZT) and Pb(Mg1/3Nb2/3)O3 (PMN). The principal findings are 1) a large anisotropy between …