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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 …
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 …
Processing And Conversion Of Algae To Bioethanol, Sara Katherine Kampfe
Processing And Conversion Of Algae To Bioethanol, Sara Katherine Kampfe
Dissertations, Theses, and Masters Projects
No abstract provided.
Optical Control Of Ultrafast Spin -Wave Relaxation By Magnetic Anisotropy In A Ferromagnet, Kevin James Smith
Optical Control Of Ultrafast Spin -Wave Relaxation By Magnetic Anisotropy In A Ferromagnet, Kevin James Smith
Dissertations, Theses, and Masters Projects
This thesis presents an investigation of the damping of spin waves in ferromagnetic Au(3 nm)/Ni(10 nm)/MgO(001) thin films using the time-resolved Magneto-optical Kerr Effect (TR-MOKE) and ferromagnetic resonance (FMR) techniques. In the optical measurements, a 150 fs, 800 nm laser beam pulse is split into pump and probe components. The pump pulse, containing most of the beam energy, thermally excites coherent spin precession. The weaker probe pulse, time-delayed by a variable beam path, captures the magnetization dynamics via the polar MOKE effect, and oscillations are observed as a function of external field amplitude and direction. The extracted precession frequency is …
Synthesis And Field Emission Properties Of Carbon Nanostructures, Kun Hou
Synthesis And Field Emission Properties Of Carbon Nanostructures, Kun Hou
Dissertations, Theses, and Masters Projects
This dissertation focuses on developing carbon nanostructures for application as the electron emissive material in novel back-gated triode field emission devices. The synthesis, characterization, and field emission properties of carbon nanostructures, including 1-D carbon nanofibers (CNF), 2-D carbon nanosheets (CNS), and chromium oxide coated carbon nanosheets (CrOx-CNS), are presented in this work.;First, we have fabricated aligned carbon nanofiber based back-gated triode field emission devices and confirmed the operation of these devices. 1-D carbon nanofibers were directly synthesized on blank TiW substrates using direct current plasma enhanced chemical vapor deposition. It was found that the morphology of carbon nanofibers could be …
Silicon Oxynitride: A Field Emission Suppression Coating, Nimel D. Theodore
Silicon Oxynitride: A Field Emission Suppression Coating, Nimel D. Theodore
Dissertations, Theses, and Masters Projects
We have studied coatings deposited using our inductively-coupled RF plasma ion implantation and desposition system to suppress field emission from large, 3-D electrode structures used in high voltage applications, like those used by Thomas Jefferson National Accelerator Facility in their DC-field photoelectron gun. Currently time and labor-intensive hand-polishing procedures are used to minimize field emission from these structures. Previous work had shown that the field emission from polished stainless steel (27 muA of field-emitted current at 15 MV/m) could be drastically reduced with simultaneous deposition of sputtered silicon dioxide during nitrogen implantation (167 pA of field-emitted current at 30 MV/m). …
Optical Characterization Of Ferromagnetic Heterostructure *Interfaces And Thin Films, Haibin Zhao
Optical Characterization Of Ferromagnetic Heterostructure *Interfaces And Thin Films, Haibin Zhao
Dissertations, Theses, and Masters Projects
This thesis presents optical characterizations of interfaces in ferromagnetic heterostructures and thin films used for spin polarized electronic devices. In these experiments, femtosecond laser spectroscopies are exploited to investigate the interface magnetization reversal, spin precession, and band offset, which are crucial in determining the performances of spintronic devices.;First, magnetization-induced second-harmonic-generation (MSHG) is applied to study interface magnetism in a hybrid structure containing a noncentrosymmetric semiconductor---Fe/AlGaAs. The reversal process of Fe interface layer magnetization is compared with the bulk magnetization reversal. In Fe/AlGaAs (001), the interface magnetization is found to be decoupled from the bulk magnetization based on the different switching …
Studies Of Energy Recovery Linacs At Jefferson Laboratory: 1 Gev Demonstration Of Energy Recovery At Cebaf And Studies Of The Multibunch, Multipass Beam Breakup Instability In The 10 Kw Fel Upgrade Driver, Christopher D. Tennant
Studies Of Energy Recovery Linacs At Jefferson Laboratory: 1 Gev Demonstration Of Energy Recovery At Cebaf And Studies Of The Multibunch, Multipass Beam Breakup Instability In The 10 Kw Fel Upgrade Driver, Christopher D. Tennant
Dissertations, Theses, and Masters Projects
An energy recovering linac (ERL) offers an attractive alternative for generating intense electron beams by approaching the operational efficiency of a storage ring while maintaining the superior beam quality typical of a linear accelerator. Two primary physics challenges exist in pushing the frontier of ERL performance. The first is energy recovering a high energy beam while demonstrating operational control of two coupled beams in a common transport channel. The second is controlling the high average current effects in ERLs, specifically a type of beam instability called multipass beam breakup (BBU). This work addresses each of these issues.;A successful 1 GeV …
Ultrafast Laser Spectroscopy Of Half -Metallic Chromium Dioxide, Hailong Huang
Ultrafast Laser Spectroscopy Of Half -Metallic Chromium Dioxide, Hailong Huang
Dissertations, Theses, and Masters Projects
This thesis presents ultrafast laser pump-probe differential transmission experiments on epitaxial CrO2 (110). The experiments were conducted at the wavelengths of 600 nm, 800 nm and 1200 nm, corresponding to the transition energies of 2 eV, 1.5 eV and 1 eV respectively. The wavelength dependent results, comparing with linear optical absorption, revealed the electronic structure of the material. The experimental results also showed polarization dependence of the probe beams. This is attributed to the electronic orbital anisotropy.;Temperature dependence was observed in the pump-probe experiments. The ultrafast transmission data show similar temperature dependence as ultrafast MOKE (Magneto-Optical Kerr Effect) data. A …
Virtual Path Bandwidth Distribution And Capacity Allocation With Bandwidth Sharing, Karen Marie Anewalt
Virtual Path Bandwidth Distribution And Capacity Allocation With Bandwidth Sharing, Karen Marie Anewalt
Dissertations, Theses, and Masters Projects
Broadband high-speed networks, such as B-ISDN, are expected to play a dominant role in the future of networking due to their capability to service a variety of traffic types with very different bandwidth requirements such as video, voice and data. to increase network efficiency in B-ISDN and other such connection oriented networks, the concept of a virtual path (VP) has been proposed and studied in the literature. A VP is a permanent or semi-permanent reservation of capacity between two nodes. Using VPs can potentially reduce call setup delays, simplify hardware, provide quality of service performance guarantees, and reduce disruption in …
Factors Affecting Carrier Transport In Ultrafast Iii-V Compound Semiconductor Based Photodiodes, James Alexander Mcadoo
Factors Affecting Carrier Transport In Ultrafast Iii-V Compound Semiconductor Based Photodiodes, James Alexander Mcadoo
Dissertations, Theses, and Masters Projects
This dissertation describes a comparative study conducted on GaAs MSM photodetectors to assess the importance of surface effects on the optical and frequency response characteristics of MSM photodetectors. MSM photodetectors on III-V compound semiconductors are technologically important because of their applications to fiber optic communication systems. While surface effects have been previously ignored, they must be considered in assessing the ultimate performance limits of such devices, especially if nanoscale MSM photodetectors are to be used. A controlled study was carried out in which high quality devices were subjected to surface damage over a known range and the resultant effects of …
Lamb Wave Diffraction Tomography, Eugene V. Malyarenko
Lamb Wave Diffraction Tomography, Eugene V. Malyarenko
Dissertations, Theses, and Masters Projects
As the worldwide aviation fleet continues to age, methods for accurately predicting the presence of structural flaws, such as hidden corrosion and disbonds, that compromise air worthiness become increasingly necessary. Ultrasonic guided waves, Lamb waves, allow large sections of aircraft structures to be rapidly inspected. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. In addition, human inspection process tends to be highly subjective, slow and prone to errors. The only practical alternative to traditional inspection routine is a software expert system capable of interpreting data with …
Low Damage Processing And Process Characterization, Xianmin Tang
Low Damage Processing And Process Characterization, Xianmin Tang
Dissertations, Theses, and Masters Projects
Two novel plasma sources (one neutral source and one pulsed inductively coupled plasma source) and ashing process characterization were investigated. The primary goal was to characterize these source properties and develop corresponding applications. The study includes process damage assessment with these two sources and another continuous wave (13.56MHz) plasma source. A global average simulation of the pulsed discharges was also included.;The transient plasma density and electron temperature from the double probe analysis were compared with single Langmuir probe results with sheath displacement corrections in pulsed discharges (200Hz--10kHz). The equivalent resistance method can be used effectively to analyze these double probe …
Studies In Microwave And Rf Capacitively Coupled Excimer Lamp, Joseph Divine Ametepe
Studies In Microwave And Rf Capacitively Coupled Excimer Lamp, Joseph Divine Ametepe
Dissertations, Theses, and Masters Projects
A lamp that emits strongly in the 180--200 nm region is desirable because of the response of organic materials in this wavelength range. Therefore there is the demand for high-powered, efficient, and low-cost UV and VUV sources.;The purpose of this work is to construct and study two novel (low-cost) UV sources and to understand the (1) emission (180--200 nm) characteristics, (2) electron energy and (3) temperature distribution in the plasmas generated by these two novel excimer lamps.;We designed, constructed and studied (1) a probe-coupled 2.45 GHz microwave arrangement to drive Xe and KrI excimer lamps and (2) a 13.45 GHz …
Thermoelastic And Photoelastic Full-Field Stress Measurement, Deonna Faye Woolard
Thermoelastic And Photoelastic Full-Field Stress Measurement, Deonna Faye Woolard
Dissertations, Theses, and Masters Projects
Photoelasticity is an optical technique that measures the difference of the principal stresses plus the principal stress direction. A complementary technique is thermoelasticity which measures the sum of the principal stresses. Combining these two full-field, non-contact nondestructive evaluation techniques allows the individual stress components to be measured. One of the main difficulties in merging these two measurement systems is in identifying an appropriate surface coating. Thermoelasticity demands a highly emissive surface, while photoelasticity requires a thick, stress-birefringent, transparent coating with a retro-reflective backing. Two coatings have been identified that can be used for combined thermoelastic and photoelastic stress measurements: PMMA …
Wavelet-Based Digital Image Restoration, Viviana Sandor
Wavelet-Based Digital Image Restoration, Viviana Sandor
Dissertations, Theses, and Masters Projects
Digital image restoration is a fundamental image processing problem with underlying physical motivations. A digital imaging system is unable to generate a continuum of ideal pointwise measurements of the input scene. Instead, the acquired digital image is an array of measured values. Generally, algorithms can be developed to remove a significant part of the error associated with these measure image values provided a proper model of the image acquisition system is used as the basis for the algorithm development. The continuous/discrete/continuous (C/D/C) model has proven to be a better alternative compared to the relatively incomplete image acquisition models commonly used …
On-Line System Identification For Control System Applications In Particle Accelerators, Mahesh Chowdhary
On-Line System Identification For Control System Applications In Particle Accelerators, Mahesh Chowdhary
Dissertations, Theses, and Masters Projects
Particle accelerators require a number of feedback systems in order to stabilize a variety of parameters. The Continuous Electron Beam Accelerator at Thomas Jefferson National Accelerator Facility presents a unique set of control and identification problems. This accelerator produces a continuous electron beam with energies between 0.5 and 4.0 GeV to be delivered to the experimental halls. In order to meet stringent beam quality requirements specified by the experimental halls, the position and the energy of the electron beam needs to stabilized at various locations in the accelerator.;A number of noise measurement tests were conducted at various locations in the …
The Projector Basis Method For Electronic Band Structure Calculations, Christopher Haas
The Projector Basis Method For Electronic Band Structure Calculations, Christopher Haas
Dissertations, Theses, and Masters Projects
Over the last several decades, two methods have emerged as the standard tools for the calculation of electronic band structures. These methods, the Car-Parinello plane wave method and the linear augmented plane wave method (LAPW), each have strengths and weaknesses in different regimes of physical problems. The Car-Parinello algorithm is ideal for calculations with soft pseudopotentials and large numbers of atoms. The LAPW method, on the other hand, easily handles all-electron and hard-core pseudopotential calculations with a small number of atoms. The projector basis method, presented here, is a hybrid mixed basis method which allows the calculation of moderately large …
Beam Dynamics In The Cebaf Superconducting Cavities, Zenghai Li
Beam Dynamics In The Cebaf Superconducting Cavities, Zenghai Li
Dissertations, Theses, and Masters Projects
This work is a study of beam dynamics in the CEBAF superconducting cavities under the influence of the fields generated by externally applied RF and beam particles.;A full 3-D modeling of the CEBAF 5-cell superconducting cavity is carried out. Details of the modeling with MAFIA are discussed. Multipole fields due to the asymmetric couplers are studied by means of 3-D Fourier transforms. The cavity steering and focusing of the multipole fields are studied. Experimental measurements of these effects are performed to validate the modeling. Evaluation of the cavity misalignment is discussed. The emittance degradation effects in the CEBAF superconducting linacs …
Constrained Least-Squares Digital Image Restoration, Rajeeb Hazra
Constrained Least-Squares Digital Image Restoration, Rajeeb Hazra
Dissertations, Theses, and Masters Projects
The design of a digital image restoration filter must address four concerns: the completeness of the underlying imaging system model, the validity of the restoration metric used to derive the filter, the computational efficiency of the algorithm for computing the filter values and the ability to apply the filter in the spatial domain. Consistent with these four concerns, this dissertation presents a constrained least-squares (CLS) restoration filter for digital image restoration. The CLS restoration filter is based on a comprehensive, continuous-input/discrete- processing/continuous-output (c/d/c) imaging system model that accounts for acquisition blur, spatial sampling, additive noise and imperfect image reconstruction. The …
The Effects Of Granularity On The Microwave Surface Impedance Of High Kappa Superconductors, Stephen Keith Remillard
The Effects Of Granularity On The Microwave Surface Impedance Of High Kappa Superconductors, Stephen Keith Remillard
Dissertations, Theses, and Masters Projects
The microwave surface impedance of granular high temperature superconductors is an important figure of merit for technological applications. Because the behavior of the granular materials deviates significantly from that of the ideal defect free superconductors, the loss mechanisms are not fully understood. This dissertation seeks to quantify the contribution of granularity to centimeter wave and millimeter wave losses. By understanding these losses, the superconductive coupling between neighboring grains can also be understood.;The weakly coupled grain model is used as a phenomenological description of the microwave surface impedance. The granular superconducting surface is modelled as an effective resistively shunted Josephson junction. …
Petroleum Degradation By Naturally Occurring Populations Of Marine Bacteria From Middle Atlantic Outer Continental Shelf Waters, Alexander Maccubbin
Petroleum Degradation By Naturally Occurring Populations Of Marine Bacteria From Middle Atlantic Outer Continental Shelf Waters, Alexander Maccubbin
Dissertations, Theses, and Masters Projects
Bacterial populations indigenous to surface (1 m) waters of the Middle Atlantic Outer Continental Shelf were sampled at seasonal intervals to determine the abundance and distribution of petroleum-degrading (HC) and "total" heterotrophic (HET) bacteria. Simultaneously, unweathered South Louisiana crude oil (SLCO) was added to aliquots of surface water samples to evaluate rates and patterns of degradation of hydrocarbon. Degradation was studied using selected nutrient and temperature regimes in both closed flask and prototype "open" or continuous dilution systems. HET bacterial levels generally decreased with distance from land (x inshore = 6 x 10('4) MPN/ml to x offshore = 6 x …
Most Probable Magnetohydrostatic Equilibria For Tokamaks And Reversed Field Pinches, John Joseph Ambrosiano
Most Probable Magnetohydrostatic Equilibria For Tokamaks And Reversed Field Pinches, John Joseph Ambrosiano
Dissertations, Theses, and Masters Projects
The determination of magnetohydrostatic equilibria usually requires that two of the equilibrium functions be given. as there is usually no a priori basis for specifying the form of these two functions, the functions and the equilibria they determine may be considered random.;In this dissertation, the author reviews a recent statistical method for determining the equilibrium of an axially symmetric cylindrical plasma which is most probable (in the maximum entropy sense) given four global constraints (i.e., energy, magnetic helicity, longitudinal magnetic flux, and longitudinal current flux). Previous results from this model have been limited to non-negative random equilibrium functions (B(,z), J(,z), …
Nonlinear Evolution Of The Magnetohydrodynamic Sheet Pinch, William H. Matthaeus
Nonlinear Evolution Of The Magnetohydrodynamic Sheet Pinch, William H. Matthaeus
Dissertations, Theses, and Masters Projects
No abstract provided.
Bacterial Response To Crude Oil Spillage In A Salt Marsh, Russell Paul Herwig
Bacterial Response To Crude Oil Spillage In A Salt Marsh, Russell Paul Herwig
Dissertations, Theses, and Masters Projects
No abstract provided.
Cross Field Current Instabilites In A Vlasov Plasma, Don S. Lemons
Cross Field Current Instabilites In A Vlasov Plasma, Don S. Lemons
Dissertations, Theses, and Masters Projects
No abstract provided.
The Effects Of Petroleum On The Salt Marsh Ecosystem, James L. Lake
The Effects Of Petroleum On The Salt Marsh Ecosystem, James L. Lake
Dissertations, Theses, and Masters Projects
No abstract provided.
Stability And Spectra Of The Bumpy Theta Pinch, Thomas E. Cayton
Stability And Spectra Of The Bumpy Theta Pinch, Thomas E. Cayton
Dissertations, Theses, and Masters Projects
No abstract provided.
Pressure Anisotropy Effects On The Stability Of The Guiding Center Model Of The Bumpy Theta Pinch, Michael J. Schmidt
Pressure Anisotropy Effects On The Stability Of The Guiding Center Model Of The Bumpy Theta Pinch, Michael J. Schmidt
Dissertations, Theses, and Masters Projects
No abstract provided.
A Theoretical Investigation Of Electromagnetic Waves Obliquely Incident Upon A Plasma Slab, Calvin Thomas Swift
A Theoretical Investigation Of Electromagnetic Waves Obliquely Incident Upon A Plasma Slab, Calvin Thomas Swift
Dissertations, Theses, and Masters Projects
No abstract provided.