Current Search:   Johnson, Michael (x)

View All Items

  • CSV Spreadsheet
(1 - 6 of 6)
MODEL STUDIES OF TIME-DEPENDENT DUCTING FOR HIGH-FREQUENCY GRAVITY WAVES AND ASSOCIATED AIRGLOW RESPONSES IN THE UPPER ATMOSPHERE
Title
MODEL STUDIES OF TIME-DEPENDENT DUCTING FOR HIGH-FREQUENCY GRAVITY WAVES AND ASSOCIATED AIRGLOW RESPONSES IN THE UPPER ATMOSPHERE.
Creator
Yu, Yonghui, Johnson, Michael, University of Central Florida
Abstract / Description
This doctoral dissertation has mainly concentrated on modeling studies of shorter period acoustic-gravity waves propagating in the upper atmosphere. Several cases have been investigated in the literature, which are focusing on the propagation characteristics of high-frequency gravity wave packets. The dissertation consists of five main divisions of which each has its own significance to be addressed, and these five chapters are also bridged in order with each other to present a theme about...
Show moreThis doctoral dissertation has mainly concentrated on modeling studies of shorter period acoustic-gravity waves propagating in the upper atmosphere. Several cases have been investigated in the literature, which are focusing on the propagation characteristics of high-frequency gravity wave packets. The dissertation consists of five main divisions of which each has its own significance to be addressed, and these five chapters are also bridged in order with each other to present a theme about gravity wave ducting dynamics, energetics, and airglows. The first chapter is served as an introduction of the general topic about atmospheric acoustic-gravity waves. Some of the historical backgrounds are provided as an interesting refreshment and also as a motivation reasoning this scientific research for decades. A new 2-D, time-dependent, and nonlinear model is introduced in the second chapter (the AGE-TIP model, acronymically named atmospheric gravity waves for the Earth plus tides and planetary waves). The model is developed during this entire doctoral study and has carried out almost all research results in this dissertation. The third chapter is a model application for shorter period gravity waves ducted in a thermally stratified atmosphere. In spite of mean winds the thermal ducting occurs because ducted waves are fairly common occurrences in airglow observations. One-dimensional Fourier analysis is applied to identify the ducted wave modes that reside within multiple thermal ducts. Besides, the vertical energy flux and the wave kinetic energy density are derived as wave diagnostic variables to better understand the time-resolved vertical transport of wave energy in the presence of multiple thermal ductings. The fourth chapter is also a model application for shorter period gravity waves, but it instead addresses the propagation of high-frequency gravity waves in the presence of mean background wind shears. The wind structure acts as a significant directional filter to the wave spectra and hence causes noticeable azimuthal variations at higher altitudes. In addition to the spectral analysis applied previously the wave action has been used to interpret the energy coupling between the waves and the mean flow among some atmospheric regions, where the waves are suspected to extract energy from the mean flow at some altitudes and release it to other altitudes. The fifth chapter is a concrete and substantial step connecting theoretical studies and realistic observations through nonlinearly coupling wave dynamic model with airglow chemical reactions. Simulated O (1S) (557.7 nm) airglow images are provided so that they can be compared with observational airglow images. These simulated airglow brightness variations response accordingly with minor species density fluctuations, which are due to propagating and ducting nonlinear gravity waves within related airglow layers. The thermal and wind structures plus the seasonal and geographical variabilities could significantly influence the observed airglow images. By control modeling studies the simulations can be used to collate with concurrent observed data, so that the incoherencies among them could be very useful to discover unknown physical processes behind the observed wave scenes.
Show less
Date Issued
2007
Identifier
CFE0001717, ucf:47316
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001717
TUNNELING CONDUCTANCE CHARACTERIZATION OF A QUANTUM DOT IN THE FRACTIONAL QUANTUM HALL REGIME
Title
TUNNELING CONDUCTANCE CHARACTERIZATION OF A QUANTUM DOT IN THE FRACTIONAL QUANTUM HALL REGIME.
Creator
Willard, Douglas, Johnson, Michael, University of Central Florida
Abstract / Description
This work represents a first-principles calculation of the electron tunneling current into quantum dots in the fractional quantum Hall effect regime. The system under consideration consists of an idealized Scanning Tunneling Microscope (STM) tip and a quantum dot with disk geometry and interacting electrons in a transverse magnetic field. Within the context of this model the tunneling current between the STM tip and the dot is examined for spin-polarized electrons at and around a filling...
Show moreThis work represents a first-principles calculation of the electron tunneling current into quantum dots in the fractional quantum Hall effect regime. The system under consideration consists of an idealized Scanning Tunneling Microscope (STM) tip and a quantum dot with disk geometry and interacting electrons in a transverse magnetic field. Within the context of this model the tunneling current between the STM tip and the dot is examined for spin-polarized electrons at and around a filling factor of 1/3. The current expression is based on a second-quantized Hamiltonian in which electrons in the dot are interacting, confined, and restricted to the lowest Landau level, necessary to capture the physics of the fractional quantum Hall effect. The Hamiltonian includes simple approximations for the STM tip and the tip-dot tunneling. An exact analytic expression for the first-order tunneling current is derived using a Green's function approach. To calculate the tunneling current numerically the infinite Hilbert space of the dot is truncated to have a finite dimension within the lowest Landau level. This simplification is appropriate for a low temperature system in the fractional quantum Hall regime because of the finite size of the quantum dot and the large energy gap between Landau levels. The tunneling current is then solved in two steps. First, many-electron energy eigenstates are calculated from the truncated Hamiltonian by numerical diagonalization. This is carried out for varying numbers of electrons N. The energy eigenstates form a set of complete basis states of the system and are used in the expression for the tunneling current. In the second step, the chemical potential in the dot is chosen to select a desired number of electrons and the tunneling current evaluated. We have carried out this program for filling factors near 1/3 while modulating the system parameters of interest to determine functional dependencies.
Show less
Date Issued
2011
Identifier
CFE0003990, ucf:48677
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003990
THE DISPARITY OF MILITARY POWER BETWEEN THE UNITED STATES, EUROPE AND ITS EFFECT ON TRANSTALANTIC DEFENSE PROJECT COOPERATION
Title
THE DISPARITY OF MILITARY POWER BETWEEN THE UNITED STATES, EUROPE AND ITS EFFECT ON TRANSTALANTIC DEFENSE PROJECT COOPERATION.
Creator
Johnson, John-Michael, Houghton, David, University of Central Florida
Abstract / Description
This study investigated what determines successful transatlantic defense policy cooperation and how that cooperation can reduce the military capability gap between the United States and its European NATO allies. It examines the differing defense policies and defense capabilities between the United States and its European NATO allies. Several theories in International Relations were also used as a foundation for the argument that cooperation is needed. The approach to defense policy is very...
Show moreThis study investigated what determines successful transatlantic defense policy cooperation and how that cooperation can reduce the military capability gap between the United States and its European NATO allies. It examines the differing defense policies and defense capabilities between the United States and its European NATO allies. Several theories in International Relations were also used as a foundation for the argument that cooperation is needed. The approach to defense policy is very different between the United States and Europe. The strategic vision of the world of both parties differs as well. Policy, doctrine and defense projects are all taken into consideration and analyzed. Based on the results of the analysis of policy and doctrines, the policy recommendation is that there should be more cooperation on defense policy planning, military doctrine and defense projects conducted in the effective fashion of current successful cases. The European NATO members will also need to cooperate on such policy if the military capability gap is to be lessened.
Show less
Date Issued
2008
Identifier
CFE0002417, ucf:47762
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002417
Childhood Predictors in the Severity of Combat Related Posttraumatic Stress Disorder Among Veterans with Combat Related Exposure
Title
Childhood Predictors in the Severity of Combat Related Posttraumatic Stress Disorder Among Veterans with Combat Related Exposure.
Creator
Bermes, Michael, Abel, Eileen, Burg, Mary, Steen, Julie, Johnson, Ann, University of Central Florida
Abstract / Description
Emerging research suggests that childhood adversities may increase both the risk and symptomology of posttraumatic stress disorder (PTSD) in our veteran population. Over 40% of our reintegrating military veterans return with significant mental health issues led by combat-related PTSD. PTSD impacts veterans in numerous areas including unemployment, increased criminal justice involvement, increased treatment costs, divorce, co-morbid mental illness, greater levels of domestic violence,...
Show moreEmerging research suggests that childhood adversities may increase both the risk and symptomology of posttraumatic stress disorder (PTSD) in our veteran population. Over 40% of our reintegrating military veterans return with significant mental health issues led by combat-related PTSD. PTSD impacts veterans in numerous areas including unemployment, increased criminal justice involvement, increased treatment costs, divorce, co-morbid mental illness, greater levels of domestic violence, homelessness, high college dropout rates, suicide, and long term health problems. The purpose of this study is to investigate the impact of childhood adversities (abuse, neglect, and poverty) upon the severity of combat-related PTSD in veteran populations. Specifically, the researcher examines the direct effects of: (1) childhood trauma; (2) childhood neglect; and (3) childhood poverty (as assessed based on socioeconomic status [SES]) upon the severity of combat-related PTSD. This study of student veterans (n=102) receiving services from a veteran service center at a major metropolitan university in Central Florida is a non-experimental, explanatory, retrospective survey design using structural equation modeling (SEM) to test the relationships among study variables. Findings strongly supported a relationship between childhood trauma and neglect and the severity of combat-related PTSD. Similarly, findings also supported that no relationship existed between childhood SES and the severity of combat-related PTSD. Both childhood trauma and neglect were significantly associated with combat-related PTSD at an even greater effect than that of combat exposure. SES was not found to be significant in the severity of combat-related PTSD. The findings suggest that preventive screening policies to reduce costs and severity of combat-related PTSD might be needed.
Show less
Date Issued
2013
Identifier
CFE0004815, ucf:49739
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004815
The Workplace Consequences of Obesity: Impacts on the Organization, the Employee, and the Proximal Coworker
Title
The Workplace Consequences of Obesity: Impacts on the Organization, the Employee, and the Proximal Coworker.
Creator
Johnson, Michael, Schminke, Marshall, Folger, Robert, Taylor, Shannon, Galperin, Bella, University of Central Florida
Abstract / Description
Obesity is a condition affecting billions of people around the world. Its societal, psychological, and health outcomes have been well documented across multiple disciplines. Moreover, obesity leads to serious workplace outcomes for the organization, the obese individual, and the coworkers working around the obese employee. With this multi-chapter dissertation, I review the literature on the workplace consequences of obesity and extend one potentially fruitful area within this literature base:...
Show moreObesity is a condition affecting billions of people around the world. Its societal, psychological, and health outcomes have been well documented across multiple disciplines. Moreover, obesity leads to serious workplace outcomes for the organization, the obese individual, and the coworkers working around the obese employee. With this multi-chapter dissertation, I review the literature on the workplace consequences of obesity and extend one potentially fruitful area within this literature base: obesity's impact on a proximal employee.Chapter 1 reviews the workplace consequences associated with obesity. The purpose is to evaluate and integrate this multidisciplinary literature so that management scholars can take up the study of obesity. Although a limited amount of work is being done in management, this work is stagnant and ignoring the larger body of literature from other areas. Addressing this weakness, this chapter accomplishes three goals. First, it reviews the empirical literature and conceptual foundations that have examined the workplace consequences of obesity. Second, it develops an integrated conceptual model of obesity's impact on workplace outcomes, with particular attention to the processes by which obesity is associated with these outcomes. Third, it presents key unanswered questions and directions for future research.Chapter 2 explores a new target for the impact of obesity, the non-obese coworker working around the obese employee. This chapter considers how an employee's obesity can affect a proximal coworker's job performance. To do so, it considers the three people: an observer (Person A), an obese employee (Person B), and a non-obese coworker (Person C). To date, the main theoretical framework has only considered ratings in the mind of an observer (Person A) and how the negative attitudes associated with obesity (Person B) can spill over onto a proximal worker (Person C). This leads an observer (Person A) to rate the coworker's (Person C) performance more negatively than a coworker not working around an obese employee (Person B). However, beyond the impact of obesity on the subjective evaluations by an observer (Person A), there is reason to believe that the non-obese employee (Person C) may be impacted in such a way to affect actual job performance. Accordingly, I competitively test three theoretical perspectives that may explain the processes by which a coworker's obesity (Person B) may impact a proximal coworker's (Person C) job performance. One of these perspectives (stereotype activation theory), receives consistent support across samples.Chapter 3 presents a concluding discussion. I consider lessons learned from Chapter 2 and integrate these with the literature reviewed in Chapter 1.
Show less
Date Issued
2017
Identifier
CFE0006608, ucf:51270
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006608
Nonlinear dynamic modeling, simulation and characterization of the mesoscale neuron-electrode interface
Title
Nonlinear dynamic modeling, simulation and characterization of the mesoscale neuron-electrode interface.
Creator
Thakore, Vaibhav, Hickman, James, Mucciolo, Eduardo, Rahman, Talat, Johnson, Michael, Behal, Aman, Molnar, Peter, University of Central Florida
Abstract / Description
Extracellular neuroelectronic interfacing has important applications in the fields of neural prosthetics, biological computation and whole-cell biosensing for drug screening and toxin detection. While the field of neuroelectronic interfacing holds great promise, the recording of high-fidelity signals from extracellular devices has long suffered from the problem of low signal-to-noise ratios and changes in signal shapes due to the presence of highly dispersive dielectric medium in the neuron...
Show moreExtracellular neuroelectronic interfacing has important applications in the fields of neural prosthetics, biological computation and whole-cell biosensing for drug screening and toxin detection. While the field of neuroelectronic interfacing holds great promise, the recording of high-fidelity signals from extracellular devices has long suffered from the problem of low signal-to-noise ratios and changes in signal shapes due to the presence of highly dispersive dielectric medium in the neuron-microelectrode cleft. This has made it difficult to correlate the extracellularly recorded signals with the intracellular signals recorded using conventional patch-clamp electrophysiology. For bringing about an improvement in the signal-to-noise ratio of the signals recorded on the extracellular microelectrodes and to explore strategies for engineering the neuron-electrode interface there exists a need to model, simulate and characterize the cell-sensor interface to better understand the mechanism of signal transduction across the interface. Efforts to date for modeling the neuron-electrode interface have primarily focused on the use of point or area contact linear equivalent circuit models for a description of the interface with an assumption of passive linearity for the dynamics of the interfacial medium in the cell-electrode cleft. In this dissertation, results are presented from a nonlinear dynamic characterization of the neuroelectronic junction based on Volterra-Wiener modeling which showed that the process of signal transduction at the interface may have nonlinear contributions from the interfacial medium. An optimization based study of linear equivalent circuit models for representing signals recorded at the neuron-electrode interface subsequently proved conclusively that the process of signal transduction across the interface is indeed nonlinear. Following this a theoretical framework for the extraction of the complex nonlinear material parameters of the interfacial medium like the dielectric permittivity, conductivity and diffusivity tensors based on dynamic nonlinear Volterra-Wiener modeling was developed. Within this framework, the use of Gaussian bandlimited white noise for nonlinear impedance spectroscopy was shown to offer considerable advantages over the use of sinusoidal inputs for nonlinear harmonic analysis currently employed in impedance characterization of nonlinear electrochemical systems. Signal transduction at the neuron-microelectrode interface is mediated by the interfacial medium confined to a thin cleft with thickness on the scale of 20-110 nm giving rise to Knudsen numbers (ratio of mean free path to characteristic system length) in the range of 0.015 and 0.003 for ionic electrodiffusion. At these Knudsen numbers, the continuum assumptions made in the use of Poisson-Nernst-Planck system of equations for modeling ionic electrodiffusion are not valid. Therefore, a lattice Boltzmann method (LBM) based multiphysics solver suitable for modeling ionic electrodiffusion at the mesoscale neuron-microelectrode interface was developed. Additionally, a molecular speed dependent relaxation time was proposed for use in the lattice Boltzmann equation. Such a relaxation time holds promise for enhancing the numerical stability of lattice Boltzmann algorithms as it helped recover a physically correct description of microscopic phenomena related to particle collisions governed by their local density on the lattice. Next, using this multiphysics solver simulations were carried out for the charge relaxation dynamics of an electrolytic nanocapacitor with the intention of ultimately employing it for a simulation of the capacitive coupling between the neuron and the planar microelectrode on a microelectrode array (MEA). Simulations of the charge relaxation dynamics for a step potential applied at t = 0 to the capacitor electrodes were carried out for varying conditions of electric double layer (EDL) overlap, solvent viscosity, electrode spacing and ratio of cation to anion diffusivity. For a large EDL overlap, an anomalous plasma-like collective behavior of oscillating ions at a frequency much lower than the plasma frequency of the electrolyte was observed and as such it appears to be purely an effect of nanoscale confinement. Results from these simulations are then discussed in the context of the dynamics of the interfacial medium in the neuron-microelectrode cleft. In conclusion, a synergistic approach to engineering the neuron-microelectrode interface is outlined through a use of the nonlinear dynamic modeling, simulation and characterization tools developed as part of this dissertation research.
Show less
Date Issued
2012
Identifier
CFE0004797, ucf:49718
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004797