Signal Subspace Processing in the Beam Space of a True Time Delay Beamformer Bank

A number of techniques for Radio Frequency (RF) source location for wide bandwidth signals have been described that utilize coherent signal subspace processing, but often suffer from limitations such as the requirement for preliminary source location estimation, the need to apply the technique iteratively, computational expense or others. This dissertation examines a method that performs subspace processing of the data from a bank of true time delay beamformers. The spatial diversity of the beamformer bank alleviates the need for a preliminary estimate while simultaneously reducing the dimensionality of subsequent signal subspace processing resulting in computational efficiency. The pointing direction of the true time delay beams is independent of frequency, which results in a mapping from element space to beam space that is wide bandwidth in nature. This dissertation reviews previous methods, introduces the present method, presents simulation results that demonstrate the assertions, discusses an analysis of performance in relation to the Cramer-Rao Lower Bound (CRLB) with various levels of noise in the system, and discusses computational efficiency. One limitation of the method is that in practice it may be appropriate for systems that can tolerate a limited field of view. The application of Electronic Intelligence is one such application. This application is discussed as one that is appropriate for a method exhibiting high resolution of very wide bandwidth closely spaced sources and often does not require a wide field of view. In relation to system applications, this dissertation also discusses practical employment of the novel method in terms of antenna elements, arrays, platforms, engagement geometries, and other parameters. The true time delay beam space method is shown through modeling and simulation to be capable of resolving closely spaced very wideband sources over a relevant field of view in a single algorithmic pass, requiring no course preliminary estimation, and exhibiting low computational expense superior to many previous wideband coherent integration techniques

Signal Subspace Processing in the Beam Space of a True Time Delay Beamformer Bank

A number of techniques for Radio Frequency (RF) source location for wide bandwidth signals have been described that utilize coherent signal subspace processing, but often suffer from limitations such as the requirement for preliminary source location estimation, the need to apply the technique iteratively, computational expense or others. This dissertation examines a method that performs subspace processing of the data from a bank of true time delay beamformers. The spatial diversity of the beamformer bank alleviates the need for a preliminary estimate while simultaneously reducing the dimensionality of subsequent signal subspace processing resulting in computational efficiency. The pointing direction of the true time delay beams is independent of frequency, which results in a mapping from element space to beam space that is wide bandwidth in nature. This dissertation reviews previous methods, introduces the present method, presents simulation results that demonstrate the assertions, discusses an analysis of performance in relation to the Cramer-Rao Lower Bound (CRLB) with various levels of noise in the system, and discusses computational efficiency. One limitation of the method is that in practice it may be appropriate for systems that can tolerate a limited field of view. The application of Electronic Intelligence is one such application. This application is discussed as one that is appropriate for a method exhibiting high resolution of very wide bandwidth closely spaced sources and often does not require a wide field of view. In relation to system applications, this dissertation also discusses practical employment of the novel method in terms of antenna elements, arrays, platforms, engagement geometries, and other parameters. The true time delay beam space method is shown through modeling and simulation to be capable of resolving closely spaced very wideband sources over a relevant field of view in a single algorithmic pass, requiring no course preliminary estimation, and exhibiting low computational expense superior to many previous wideband coherent integration techniques

Molecular Dynamics Simulations of Cascade Evolution near Pre-Existing Defects

Radiation damage causes significant changes to material microstructure and properties as a result of the processes of atomic defect creation followed by the inherently multiscale defect diffusion and reaction processes. In particular, the overlap of displacement cascades is believed important in the development of visible defect clusters in thin film, in-situ ion irradiation studies. In this work, we use molecular dynamics simulations to investigate how impurities and damage induced by displacement cascades impact damage creation as well as the mobility of a pre-existing interstitial-type dislocation loop in BCC iron. It is well known that impurities, such as oxygen, carbon, and nitrogen impact the mobility of interstitial dislocation loops, and are likely responsible for the difference in loop diffusivities between computer simulations and experimental observations by transmission electron microscopy. We have used molecular dynamics simulations to evaluate whether a displacement cascade could de-trap an interstitial cluster from interstitial impurity atoms. By varying the energy and directional velocity of the primary knock on atom (PKA), we observe how the trapped defect reacts with the cascade damage. Our simulation results reveal that cascades with PKA energy greater than 10 keV can cause the loop to de-trap from impurities, but the loop often rapidly becomes trapped in the cascade debris. Furthermore, on several occasions, the cascade induces a change in orientation, or Burgers vector, in addition to modifying the size of the dislocation loop. The thesis summarizes the molecular dynamics simulation results as a function of PKA energy, distance from the trapped loop and direction, as well as the effect of loop size, in terms of the probability for de-trapping and subsequent diffusion. Furthermore, molecular dynamics simulations results will be presented that quantify on the impact of pre-existing vacancies on defect production as a function of PKA energy and concentration. These simulation results provide a basis to inform cluster dynamics models of dislocation loop evolution in irradiated ferritic/martensitic alloys

Novel Approaches to Metal Ion Sensing

The primary focus of this dissertation is the development of new chemical analyses for metal ions. Approaches combining electrochemical, spectroscopic, analytical, inorganic, and materials chemistry have been used to investigate novel methods for metal ion sensing. Topics discussed in this dissertation include pyridinium-functionalized sol-gel films for the enhanced electrochemical analysis of Cr(VI), pyridinium-functionalized sol-gel monoliths for the optical determination of Cr(VI), the use of the electrochemical quartz crystal microbalance for the determination of Pd(II), novel electrochemical and spectroscopic approaches to Fe(III) sensing, and the electrochemical quartz crystal microbalance investigation of the Cr(III)-DTPA complex

Neural mechanisms of short-term visual plasticity and cortical disinhbition

Deafferented cortical visual areas exhibit topographical plasticity such that their constituent neural populations adapt to the loss of sensory input through the expansion and eventual remapping of receptive fields to new regions of space. Such representational plasticity is most compelling in the long-term (months or years) but begins within seconds of retinal deafferentation (short-term plasticity). The neural mechanism proposed to underlie topographical plasticity is one of disinhibition whereby long-range horizontal inputs are "unmasked" by a reduction in local inhibitory drive. In this dissertation, four experiments investigated the neural mechanisms of short-term visual plasticity and disinhibition in humans using a combination of psychophysics and event-related potentials (ERPs). Short-term visual plasticity was induced using a stimulus-induced analog of retinal deafferentation known as an artifical scotoma. Artificial scotomas provide a useful paradigm for the study of short-term plasticity as they induce disinhibition but are temporary and reversible. Experiment 1 measured contrast response functions from within the boundaries of an artificial scotoma and evaluated them relative to a sham control condition. Changes in the contrast response function suggest that disinhibition can be conceived of in terms of two dependent but separable processes: receptive field expansion and unrestricted neural gain. A two-process model of disinhibition is proposed. A complementary ERP study (Experiment 2) recorded visual evoked potentials elicited by probes appearing within the boundaries of an artificial scotoma. Results revealed a neural correlate of disinhibition consistent with origins in striate and extrastriate visual areas. Experiment 3 and 4 were exploratory examinations of the representation of space surrounding an artificial scotoma and revealed a neural correlate of invading activity from normal cortex. Together, the results of these four studies strengthen the understanding of the neural mechanisms that underlie short-term plasticity and provide a conceptual framework for their evaluation.Ph.D.Committee Chair: Dr. Paul Corballis, Ph.D.; Committee Member: Dr. Daniel Spieler, Ph.D.; Committee Member: Dr. Eric Schumacher, Ph.D.; Committee Member: Dr. Krish Sathian, M.D., Ph.D.; Committee Member: Dr. Randall Engle, Ph.D

Development and Application of 3-D Fuel Performance Modeling to Assess Missing Pellet Surface Influence on Pellet Clad Interaction and Clad Failure

In the late 1970s PCI related failures caused the implementation of startup ramp restrictions. These ramp restrictions where intended to reduce the stresses caused by pellet cladding contact. These ramp restrictions had a significant impact on Westinghouse fueled PWRs, reducing PCI related failure until 2003. Through investigation into these fuel rod failures lead to the conclusion that missing pellet surfaces (MPS) were the root cause of the failures. MPS are local geometric defects in nuclear fuel pellets that result from pellet mishandling or the manufacturing process. The presence of MPS defects can cause stress concentrations in the clad of sufficient magnitude to produce through-wall cladding failure for certain combinations of fuel burnup, and reactor power level or power change. Consequently, the impact of potential MPS defects has significant ly limited the rate of power increase, or ramp rate, in both pressurized and boiling water reactors (PWRs and BWRs, respectively). Improved three-dimensional (3-D) fuel performance models of MPS defect geometry can provide better understanding of the probability for pellet clad mechanical interaction (PCMI), and correspondingly the available margin against cladding failure by stress corrosion cracking (SCC). The Bison fuel performance code has been developed within the Consortium of Advanced Simulations of Light Water Reactors (CASL) to consider the inherently multi-physics and multi-dimensional mechanisms that control fuel behavior, including cladding stress concentrations resulting from MPS defects. Bison is built upon the Multi-physics Object-Oriented Simulation Environment (MOOSE) developed at Idaho National Laboratory (INL). MOOSE is a massively parallel finite element computational system that uses a Jacobian-free, Newton-Krylov (JFNK) method to solve coupled systems of non-linear partial differential equations. In addition, the MOOSE framework provides the ability to effectively use massively parallel computational capabilities needed to create high fidelity 3-D models of a fuel rod, as well as full-length R-Z rods, and R-Theta geometric representation. This PhD dissertation documents my contributions to the development of Bison, specifically focused on verification and validation of a 2-D, axi-symmetric version of Bison through benchmarking comparisons to Falcon model predictions and Halden Instrumented Fuel Assembly (IFA) experiments of both thermal and mechanical behavior. Initial benchmark comparisons indicate that Bison predictions agree quite well with 2-D Falcon predictions and Halden experimental data on fuel centerline temperature but that further developments are necessary for some models, including fission gas release and gaseous swelling. The mechanical behavior benchmarking study has compared predictions of clad deformation to dilatational measurements, and the results show promising agreement. Subsequently, this dissertation documents my evaluation of the cladding hoop stress distributions as a function of MPS defect geometry and the presence of discrete pellet cracks for a set of typical operating conditions in a PWR fuel rod, as a function of reactor operating history. These results provide a first step in a probabilistic approach to assess cladding failure during power maneuvers. My research provides insight into how varying pellet defect geometries affect the distribution of the cladding stress, as well as the temperature distributions within the fuel and clad; and are used to develop stress concentration factors for comparing 2-D and 3-D models. Finally, the objective of this dissertation is to develop a methodology to determine rod failure, and then to utilize the resulting failure criteria to evaluate specific historical MPS and PCI failures

Diffusion of solar cosmic rays and the power spectrum of the interplanetary magnetic field

Solar cosmic ray diffusion and interplanetary magnetic field power spectru

DOES SPIRITUALITY REDUCE THE EFFECTS OF BURNOUT?

Burnout is a topic that is drawing an increasing amount of attention in the social work field. The compassion and emotional energy that is used daily by these service providers can cause them to experience emotional exhaustion, depersonalization, and reduced personal accomplishment. The effects of burnout are detrimental on several levels. Staff will experience decreased interest and efficiency in their work and may even leave their place of employment. Clients will not receive the help that they require and agencies will suffer from staff turnover and lowered productivity. Utilizing a survey including a burnout inventory and spirituality inventory, data was gathered regarding burnout and the spiritual attitudes and practices of 133 service providers. Results show that there is a negative significant relationship between depersonalization and spirituality. There was a positive significant relationship between personal accomplishment and spirituality. The correlation showed that personal accomplishment was negatively related to emotional exhaustion as well as depersonalization. These results are consistent with the literature in the way that it demonstrates that the use of spiritual beliefs and practices can reduce the effects of burnout on social workers

Impaired thermoregulatory function during dynamic exercise in multiple sclerosis

INTRODUCTION: Impairments in sudomotor function during passive whole-body heating have been reported in multiple sclerosis (MS), a demyelinating disease of the CNS that disrupts autonomic function. However, the capability of the thermoregulatory system to control body temperature during exercise has never been assessed in MS. Thus, the aim of the present study was to test the hypothesis that thermoregulatory function is impaired in MS patients compared to healthy controls (CON) exercising at similar rates of metabolic heat production. METHODS: Sweating and skin blood flow responses were compared between 12 individuals diagnosed with relapsing-remitting MS (9 females, 3 males) and 12 sex-, age-, mass- and BSA-matched healthy controls during a single bout of cycling exercise (rate of metabolic heat production: ~4.5 W/kg) for 60 min in a climate-controlled room (25 °C, 30% RH). RESULTS: Individuals with MS exhibited an attenuated increase in cumulative whole-body sweat loss after 30 min (MS: 72 ± 51; CON: 104 ± 37 g, p=0.04) and 60 min (MS: 209 ± 94; CON: 285 ± 62 g, p=0.02), as well as lower sweating thermosensitivity (MS: 0.49 ± 0.26; CON: 0.86 ± 0.30 mg/cm2/min/°C, p=0.049). Despite evidence for thermoregulatory dysfunction, there were no differences between MS and CON in esophageal or rectal temperatures at 30 or 60 min time points (p>0.05). Cutaneous vasculature responses were also not different in MS compared to CON (p>0.05). CONCLUSION: Taken together, MS blunts sweating responses during exercise while cutaneous vasculature responses are preserved. Altered mechanisms of body temperature regulation in persons with MS may lead to temporary worsening of disease symptoms and limit exercise tolerance under more thermally challenging conditions.Accepted manuscrip