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Full-Text Articles in Physical Sciences and Mathematics
Timing And Spectroscopy Requirements For A Plastic Scintillating Fiber Bundle Time-Of-Flight Neutron Spectrometer, Paul A. Clement
Timing And Spectroscopy Requirements For A Plastic Scintillating Fiber Bundle Time-Of-Flight Neutron Spectrometer, Paul A. Clement
Theses and Dissertations
The design parameters of a Time-of-Flight (TOF) neutron spectrometer composed of BCF-12 plastic scintillating fibers were investigated. A GEANT4 transport model was developed for analyzing the interaction of 2.5 MeV neutrons with a 14 x 14 BCF-12 fiber bundle. The bundle simulation demonstrated that 0.359% of all neutrons incident on the bundle will double scatter. The timing and data collection e efficiencies of a Tektronix DPO7104 series digital oscilloscope were examined to determine the signal processing requirements for future fiber bundle measurements. The minimum detectable neutron energy was computed by taking into account the bundle scintillation e efficiency, light collection …
Construction, Analysis, And Data-Driven Augmentation Of Supersaturated Designs, Alex J. Gutman
Construction, Analysis, And Data-Driven Augmentation Of Supersaturated Designs, Alex J. Gutman
Theses and Dissertations
Screening designs are used in the early stages of industrial and computer experiments to find the most important input factors affecting a system's output. They provide an economical way to remove unimportant factors from further, potentially costly, experimentation. However, when an experiment has a large number of control factors and limited number of available runs, it is infeasible to run a traditional screening design. In these situations, experimenters can use supersaturated designs. A supersaturated design is a fractional factorial design that can screen a set of k factors in n runs, where k is greater than n -1. Unfortunately, they …
Directional Thermal Emission And Absorption From Surface Microstructures In Metalized Plastics, Michael D. Seal
Directional Thermal Emission And Absorption From Surface Microstructures In Metalized Plastics, Michael D. Seal
Theses and Dissertations
Thermal emission, exhibiting antenna-like directivity, has been generated by a wide variety of both simple and complex micro-structures. The basic demonstrations of directional emission, and specific device performance evaluations, have been conducted at elevated temperatures, typically several hundred degrees Celsius. The most common applications for these high-temperature designs are thermal photo-voltaic and spectroscopic sources. A wide range of lower temperature applications, such as spacecraft thermal management and mid- to far-infrared optical train stray light management, are precluded by the cost and complexity of the fabrication processes employed. In this work, a novel fabrication and physical surface optimization of a seminal …
Spectral Analysis And Metastable Absorption Measurements Of High Pressure Capacitively And Inductively Coupled Radio-Frequency Argon Helium Discharges, Ben Eshel
Theses and Dissertations
Characterization of the excited state argon population in an argon-helium discharge is of crucial importance to the development of a continuous wave Discharge Assisted Noble Gas Laser. Experiments were conducted in the Richard W. Davis Advanced Laser Facility at AFRL on Kirtland Air Force Base, Albuquerque, NM. During these tests the capability to maintain a capactively-coupled and inductively-coupled radio-frequency discharge at pressures of 300 Torr was demonstrated. Optical Emission Spectroscopy experiments were conducted in order to examine the population distribution of the p-state in argon. The population distributions for these high-pressure and high-power cases were compared to a low-pressure, low-power …
Applied Hypergame Theory For Network Defense, Alan S. Gibson
Applied Hypergame Theory For Network Defense, Alan S. Gibson
Theses and Dissertations
Cyber operations are the most important aspect of military conflicts in the 21st century, but unfortunately they are also among the least understood. The continual battle for network dominance between attackers and defenders is considered to be a complex game. Hypergame theory is an extension of game theory that addresses the kind of games where misperception exists, as is often the case in military engagements. Hypergame theory, like game theory, uses a game model to determine strategy selection, but goes beyond game theory by examining subgames that exist within the full game. The inclusion of misperception and misinformation in the …
The Dynamic Multi-Objective Multi-Vehicle Covering Tour Problem, Joshua S. Ziegler
The Dynamic Multi-Objective Multi-Vehicle Covering Tour Problem, Joshua S. Ziegler
Theses and Dissertations
This work introduces a new routing problem called the Dynamic Multi-Objective Multi-vehicle Covering Tour Problem (DMOMCTP). The DMOMCTPs is a combinatorial optimization problem that represents the problem of routing multiple vehicles to survey an area in which unpredictable target nodes may appear during execution. The formulation includes multiple objectives that include minimizing the cost of the combined tour cost, minimizing the longest tour cost, minimizing the distance to nodes to be covered and maximizing the distance to hazardous nodes. This study adapts several existing algorithms to the problem with several operator and solution encoding variations. The efficacy of this set …
Chip-Scale Magnetic Source Of Cold Atoms, Eric A. Imhof
Chip-Scale Magnetic Source Of Cold Atoms, Eric A. Imhof
Theses and Dissertations
Numerous disruptive technologies are being hampered by the insufficient modern methods of cooling electrically neutral atoms and molecules. Microchip-based magnetic deceleration provides a cooling mechanism to slow most neutral atoms and molecules within the cost and size requirements of a real-world device. Simulations of a novel deceleration technique show 90% removal of kinetic energy from an atomic beam. An experiment is built which creates a time-dependent, decelerating magnetic field to slow an atomic beam. An atomic beam is magnetically guided 800 microns above the surface of a microchip at pressures of 10-9 Torr. A 60 independent wire microchip is …
Optimization Of Coronal Mass Ejection Ensemble Forecasting Using Wsa-Enlil With Coned Model, Jack A . Shepherd Iii
Optimization Of Coronal Mass Ejection Ensemble Forecasting Using Wsa-Enlil With Coned Model, Jack A . Shepherd Iii
Theses and Dissertations
The combination of the Wang-Sheeley-Arge (WSA) coronal model, ENLIL version 2.7, and the Coned model version 1.4 was utilized to form ensemble forecast for 21 coronal mass ejections (CMEs). The Coned model was improved by adding a weight for the associated flare location to push the propagation axis towards the flare location and an additional image was used. Fifteen CMEs were used from previous research using the Coned model version 1.3 and the results were compared to determine the improvement. The model was used again with six additional CMEs and compared to the old Coned model version 1.3 to verify …
Development Of A Spectropolarimetric Capability, Evan J. Carlson
Development Of A Spectropolarimetric Capability, Evan J. Carlson
Theses and Dissertations
A Bomem 200 series Fourier transform infrared spectrometer and FLIR Systems Inc InGaAs infrared (IR) camera was used to measure the degree of linear polarization (DOLP) from a metal and glass surfaces. This was accomplished by placing a wire grid polarizer in front of the aperture of the FTIR and IR camera to measure the polarized reflection from the target material. For the IR camera, an average of pixel counts was collected over the area of the target to measure to DOLP. Factors impacting the accuracy of the measurements from the FTIR are calibration, instrument self emission, and alignment error. …
Crystal Growth And Characterization Of Tho2 And UXTh1-XO2, Jacob G. Castilow
Crystal Growth And Characterization Of Tho2 And UXTh1-XO2, Jacob G. Castilow
Theses and Dissertations
Hydrothermal synthesis of ThO2 and UxTh1-xO2, and UOx at temperatures between 670°C and 700°C has been demonstrated. Synthesis at these temperatures is 50-80°C below prior crystal growths and represents a new lower bound of successful growth. Hydrothermal synthesis represents a cost effective, environmentally friendly way of growing bulk actinide materials of optical quality. These refractory oxide single crystals offer potential applications in thorium nuclear fuel technology, wide-band-gap uranium-based direct-conversion solid state neutron detectors, and understanding how actinide fuels age with time. ThO2 single crystals of dimensions 6.49mm x 4.89mm x 3.89 …
Pump Diode Characterization For An Unstable Diode-Pumped Alkali Laser Resonator, Chad T. Taguba
Pump Diode Characterization For An Unstable Diode-Pumped Alkali Laser Resonator, Chad T. Taguba
Theses and Dissertations
Measurements of wavelength tunability, spectral linewidth, minimum spot size, and M2 were made for a rubidium diode-pumped alkali laser (DPAL) containing a volume Bragg grating (VBG) for resonator characterization. The output wavelength of the pump diode was measured as a function of volume Bragg grating temperature. A linear relationship was observed that corresponded to an output wavelength range of 780.08 nm 0.01 nm to 780.49 nm 0.01 nm with a tuning rate of 6.1 pm/ C for a diode chassis temperature of 37 C. Rubidium D1 fuorescence spectra were recorded as the diode wavelength was scanned across its full range …
Modeling The Thermosphere As A Driven-Dissipative Thermodynamic System, William R. Frey
Modeling The Thermosphere As A Driven-Dissipative Thermodynamic System, William R. Frey
Theses and Dissertations
Thermospheric density impacts satellite position and lifetime through atmospheric drag. More accurate specification of thermospheric temperature, a key input to current models such as the High Accuracy Satellite Drag Model (HASDM), can decrease model density errors. Building on Burke et al. s driven-dissipative model (2009) the arithmetic mean temperature, T1/2 , defined by Jacchia, 1977 (J77), is modeled using the magnetospheric electric field as a driver. Three methods of treating the UV contribution to T1/2 (T1/2UV) are tested. Two model parameters, the coupling and relaxation constants, are adjusted for 38 storms from 2002 - 2008 to …
Collisional Broadening And Shift Of D1 And D2 Spectral Lines In Atomic Alkali Vapor - Noble Gas Systems, Robert D. Loper
Collisional Broadening And Shift Of D1 And D2 Spectral Lines In Atomic Alkali Vapor - Noble Gas Systems, Robert D. Loper
Theses and Dissertations
The Baranger model is used to compute collisional broadening and shift of the D1 and D2 spectral lines of M + Ng, where M = K, Rb, Cs and Ng = He, Ne, Ar, using scattering phase shift differences which are calculated from scattering matrix elements. Scattering matrix elements are calculated using the Channel Packet Method where the collisions are treated non-adiabatically and include spin-orbit and Coriolis couplings. Non-adiabatic wavepacket dynamics are determined using the split-operator method together with a unitary transformation between adiabatic and diabatic representations. Scattering phase shift differences are thermally weighted and integrated over energies ranging from …
Electronic Characteristics Of Rare Earth Doped Gan Schottky Diodes, Aaron B. Blanning
Electronic Characteristics Of Rare Earth Doped Gan Schottky Diodes, Aaron B. Blanning
Theses and Dissertations
The Schottky barrier height (SBH) was measured on GaN based diodes with three different dopant types; Gd, Er and Yb. Two methods were used to determine the SBH. The first method was the Juergen Werner method to evaluate the I-V characteristics. The calculated SBH of the diodes using this method was 1.41 ± 0.20eV, 1.71 ± 0.25eV and 1.75 ± 0.28eV for the Gd-, Er- and Yb-doped diodes respectively. It was observed that using an ad-hoc effective Richardson constant value of 0.006Axcm-2xK-2 to calculate the SBH rendered results that were in no greater than 2% disagreement (neglecting …
Neutron Spectroscopy Using Lif Thin-Film Detectors, Michael A. Ford
Neutron Spectroscopy Using Lif Thin-Film Detectors, Michael A. Ford
Theses and Dissertations
A stacked array of segmented micro-structured semiconductor neutron detectors (MSNDs) has been fabricated to perform as a neutron spectrometer simultaneously capable of differentiating fast and thermal neutrons. The MSND devices consist of thin-film perforated diodes constructed from LiF powder back-filled into an etched silicon wafer. Geant4 simulations demonstrate than an eight-layer spectrometer consisting of alternating layers of MSND and hydrogenous moderator can successfully resolve neutron energies at a resolution dependent upon the number of layers and the thickness of the adjacent moderating materials. The simulated spectrometer response was compared to that obtained experimentally with mono-energetic neutrons from a D+D neutron …
Analysis Of A Van De Graaff Generator For Emp Direct Current Survivability Testing, Robert J. Kress
Analysis Of A Van De Graaff Generator For Emp Direct Current Survivability Testing, Robert J. Kress
Theses and Dissertations
The direct current produced from the Van de Graaff (VDG) at the Air Force Research Laboratory (AFRL) has been measured and analyzed. The current pulse produced from the VDG is oscillatory. Experimental data show complete damping occurs after 8 oscillations and within 10-6 seconds. The spark gap distance and circuit resistance were varied to determine if the circuit could convert to an overdamped RLC circuit in order to reduce the oscillations. The data establishes that the VDG produces at least 3 full wave Fourier frequencies of: 3, 7, and 15 MHz ± 2.0 MHz, while the first oscillation had …
Discrimination Of Neutral Postures In Computer Based Work, Alanna R. Keith
Discrimination Of Neutral Postures In Computer Based Work, Alanna R. Keith
Theses and Dissertations
A biometric system recognizes users based on the way they physically interact with the system. In this work, we discover a common behavior that a typist consistently displays in non-trivial computer work. We sought to demonstrate three objectives: first, compelling proof that a user can be actively recognized over the course of a lengthy task via a neutral posture struck multiple times in that task; two, a sensing concept for capturing the neutral posture, and, third, an objective method for determine the level of work performed by each typist. This thesis develops a model for hand tracking using a simple …
Multipactor Discharge In High Power Microwave Systems: Analyzing Effects And Mitigation Through Simulation In Icepic, Robert L. Lloyd
Multipactor Discharge In High Power Microwave Systems: Analyzing Effects And Mitigation Through Simulation In Icepic, Robert L. Lloyd
Theses and Dissertations
Single surface multipactor in high power microwave systems was investigated computationally and analytically. The research focused upon understanding the cause and parametric dependence of the multipactor process leading to suggested methods of mitigation. System damage due to reaction was also assessed. All simulations were performed using the PIC code developed by AFRL, known as ICEPIC. In recreating the susceptibility curves that define regions of multipactor growth and decay, a discrepancy was found between previous published results and those observed in the current simulation. This was attributed to previous simulations not accounting for the magnetic component in the electromagnetic radiation incident …
Rootkit Detection Using A Cross-View Clean Boot Method, Bridget N. Flatley
Rootkit Detection Using A Cross-View Clean Boot Method, Bridget N. Flatley
Theses and Dissertations
In cyberspace, attackers commonly infect computer systems with malware to gain capabilities such as remote access, keylogging, and stealth. Many malware samples include rootkit functionality to hide attacker activities on the target system. After detection, users can remove the rootkit and associated malware from the system with commercial tools. This research describes, implements, and evaluates a clean boot method using two partitions to detect rootkits on a system. One partition is potentially infected with a rootkit while the other is clean. The method obtains directory listings of the potentially infected operating system from each partition and compares the lists to …
An Inverse Kinematic Approach Using Groebner Basis Theory Applied To Gait Cycle Analysis, Anum Barki
An Inverse Kinematic Approach Using Groebner Basis Theory Applied To Gait Cycle Analysis, Anum Barki
Theses and Dissertations
Kinematics of the human body was researched for the purposes of this study. The force protection issues of today was the motivation to research pattern recognition in the human gait cycle to identify individuals carrying a concealed load on their body. The goal of this research was to identify gait signatures of human subjects and distinguish between subjects carrying a concealed load to subjects without load. Thus, this research was focused on studying the human gait cycle as well as methods used in identifying gait signatures. The main focus herein is concerned with the movement of the lower extremities, in …
A Comparison Of Ionospheric Model Performance For International Space Station Orbits, David J. Broadwater
A Comparison Of Ionospheric Model Performance For International Space Station Orbits, David J. Broadwater
Theses and Dissertations
The Floating Potential Measurement Unit (FPMU) aboard the International Space Station (ISS) monitors the ISS charging environment and provides a unique electron density and electron temperature in-situ data source for the purpose of ionospheric model validation. An ionospheric model that accurately predicts the ISS plasma environment is desirable for ISS mission planning and situational awareness when FPMU data is unavailable. Electron densities and temperatures from four ionospheric models (International Reference Ionosphere [IRI], Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics model [CTIPe], Ionospheric Forecast Model [IFM], and Global Assimilation of Ionospheric Measurements model [GAIM]) were compared to in-situ FPMU values across a range …
Cathodoluminescence And Thermoluminescence Of Undoped Ltb And Ltb:A (A = Cu, Ag, Mn), Zachary L. Hadfield
Cathodoluminescence And Thermoluminescence Of Undoped Ltb And Ltb:A (A = Cu, Ag, Mn), Zachary L. Hadfield
Theses and Dissertations
The Department of Defense is interested in lithium tetraborate (Li2B4O7) crystals for their possible use as a solid state neutron detection material. With large concentrations of 6Li and 10B, it has a high neutron capture cross section. Furthermore, the crystal fluoresces in the presence of ionizing radiation, making it an attractive candidate for a scintillating detection device. However, there is a lack of fundamental knowledge about the material characteristics, particularly with regard to its fluorescent spectrum. Cathodoluminescence measurements were conducted on undoped and doped samples of lithium tetraborate in order to characterize …
Modeling Radioactive Decay Chains With Branching Fraction Uncertainties, Timothy M. Higley
Modeling Radioactive Decay Chains With Branching Fraction Uncertainties, Timothy M. Higley
Theses and Dissertations
This thesis is a parameter study of the effects of branching fraction uncertainty from nuclear decay on isotope quantities at later times. Development of how to calculate and accurately draw random samples of branching fractions is done. Overall effects as well as isotope quantity uncertainty distributions are also explored. Isotope quantities are calculated using exponential moments methods with transmutation matrices. Uncertainty from both half-lives and branching fractions is carried through these calculations by Monte Carlo methods. Results of the study show that uncertainty from branching fractions dominates most isotopes present from neutron fission after approximately one month. Another result is …
Modeling Sodium Iodide Detector Response Using A Parametric Equations, Neeraj Sethi
Modeling Sodium Iodide Detector Response Using A Parametric Equations, Neeraj Sethi
Theses and Dissertations
This research utilizes the relationship between source location, background radiation and detector placement to quantify an expected detector response from a 3x3 Sodium Iodide gamma detector. A parametric equation is developed to calculate the detector response as a function of distance and source photon energy. Using MCNP particle current and pulse height tally functions, backscattering photons are quantified as a function of material thickness and energy distribution. Three configurations of source - detector - scattering medium were modeled in MCNP using the pulse height tally functions, integrated over a 70keV - 360keV energy window and plotted as a function of …
Solving Point-Reactor Kinetics Equations Using Exponential Moment Methods, Paul M. Thelen
Solving Point-Reactor Kinetics Equations Using Exponential Moment Methods, Paul M. Thelen
Theses and Dissertations
A robust method of solving the reactor point kinetic equations was designed using exponential moment methods. Although the method requires a relatively large number of calculations to complete, the accuracy ensured by each individual step calculation allows larger time steps to be used. The algorithm designed was verified to converge to the correct value as step size was reduced. Additionally, the algorithm can take steps much larger than the average neutron lifetime while maintaining some precision. An error control scheme was designed based on changes observed in the results as a function of time step size. The error control adaptively …
Study Of Laminar Flame 2-D Scalar Values At Various Fuel To Air Ratios Using An Imaging Fourier-Transform Spectrometer And 2-D Cfd Analysis, Andrew J. Westman
Study Of Laminar Flame 2-D Scalar Values At Various Fuel To Air Ratios Using An Imaging Fourier-Transform Spectrometer And 2-D Cfd Analysis, Andrew J. Westman
Theses and Dissertations
This work furthers an ongoing effort to develop imaging Fourier-transform spectrometry (IFTS) for combustion diagnostics and to validate reactive-flow computational fluid dynamics (CFD) predictions. An ideal, laminar flame produced by an ethylene-fueled (C2H4) Hencken burner (25.4 x 25.4 mm2 burner) with N2 co-flow was studied using a Telops infrared IFTS featuring an Indium Antimonide (InSb), 1.5 to 5.5 µm, focal-plane array imaging the scene through a Michelson interferometer. Flame equivalency ratios of Φ = 0.81, 0.91, and 1.11 were imaged on a 128 x 200 pixel array with a 0.48 mm per pixel spatial …
Distributional Monte Carlo Methods For The Boltzmann Equation, Christopher R. Schrock
Distributional Monte Carlo Methods For The Boltzmann Equation, Christopher R. Schrock
Theses and Dissertations
Stochastic particle methods (SPMs) for the Boltzmann equation, such as the Direct Simulation Monte Carlo (DSMC) technique, have gained popularity for the prediction of flows in which the assumptions behind the continuum equations of fluid mechanics break down; however, there are still a number of issues that make SPMs computationally challenging for practical use. In traditional SPMs, simulated particles may possess only a single velocity vector, even though they may represent an extremely large collection of actual particles. This limits the method to converge only in law to the Boltzmann solution. This document details the development of new SPMs that …
Mobile Network Defense Interface For Cyber Defense And Situational Awareness, James C. Hannan
Mobile Network Defense Interface For Cyber Defense And Situational Awareness, James C. Hannan
Theses and Dissertations
Today's computer networks are under constant attack. In order to deal with this constant threat, network administrators rely on intrusion detection and prevention services (IDS) (IPS). Most IDS and IPS implement static rule sets to automatically alert administrators and resolve intrusions. Network administrators face a difficult challenge, identifying attacks against a vast number of benign network transactions. Also after a threat is identified making even the smallest policy change to the security software potentially has far-reaching and unanticipated consequences. Finally, because the administrator is primarily responding to alerts they may lose situational awareness of the network. During this research a …
Electron Damage Effects On Carbon Nanotube Thin Films, Jeremy S. Best
Electron Damage Effects On Carbon Nanotube Thin Films, Jeremy S. Best
Theses and Dissertations
This research investigated the effects of electron damage on single walled carbon nanotube (CNT) thin films. CNT thin films were irradiated by electrons with energies of 500 keV and 1 MeV to determine what damage was created in the CNT thin film structure, how it affected conductivity, and what changes were evident in the Raman spectra.
Three Dimensional Positron Annihilation Momentum Spectroscopy Of Lithium Tetraborate Crystals, Stefan B. Fagan-Kelly
Three Dimensional Positron Annihilation Momentum Spectroscopy Of Lithium Tetraborate Crystals, Stefan B. Fagan-Kelly
Theses and Dissertations
Previous endeavors in positron annihilation spectroscopy (PAS) at AFIT have resulted in the design and characterization of a second-generation three-dimensional positron annihilation momentum spectroscopy system (3DPAMSS) which combines two-dimensional angular correlation of annihilation radiation (2D ACAR) and coincident Doppler broadening of annihilation radiation (CDBAR) in order to measure electron momentum distributions in samples and thus characterize material defects. The focus of this particular research is to nondestructively measure negative defects in the crystal lattice of copper-doped, silver-doped, and undoped lithium tetraborate by 3DPAMSS spectroscopy using a Na-22 source and two high-purity germanium (HPGe) position-resolvable strip detectors. Lithium tetraborate is a …