Engineering Commons^™

Synergistic Interactions Of H2 And N2 With Molten Gallium In The Presence Of Plasma, Maria L. Carreon, Daniel F. Jaramillo-Cabanzo, Indira Chaudhuri, Madhu Menon, Mahendra K. Sunkara

Physics and Astronomy Faculty Publications

The present study examines the interaction of hydrogen and nitrogen plasmas with gallium in an effort to gain insights into the mechanisms behind the synergetic effect of plasma and a catalytic metal. Absorption/desorption experiments were performed, accompanied by theoretical-computational calculations. Experiments were carried out in a plasma-enhanced, Ga-packed, batch reactor and entailed monitoring the change in pressure at different temperatures. The results indicated a rapid adsorption/dissolution of the gas into the molten metal when gallium was exposed to plasma, even at a low temperature of 100 °C. The experimental observations, when hydrogen was used, indicate that gallium acts as a …

Generalized Ellipsometry On Complex Nanostructures And Low-Symmetry Materials, Alyssa Mock

Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research

In this thesis, complex anisotropic materials are investigated and characterized by generalized ellipsometry. In recent years, anisotropic materials have gained considerable interest for novel applications in electronic and optoelectronic devices, mostly due to unique properties that originate from reduced crystal symmetry. Examples include white solid-state lighting devices which have become ubiquitous just recently, and the emergence of high-power, high-voltage electronic transistors and switches in all-electric vehicles. The incorporation of single crystalline material with low crystal symmetry into novel device structures requires reconsideration of existing optical characterization approaches. Here, the generalized ellipsometry concept is extended to include applications for materials with …

Speckle Effects In Target-In-The-Loop Laser Beam Projection Systems, Mikhail Vorontsov

Electro-Optics and Photonics Faculty Publications

In target-in-the-loop laser beam projection scenarios typical of remote sensing, directed energy, and adaptive optics applications, a transmitted laser beam propagates through an optically inhomogeneous medium toward a target, scatters off the target’s rough surface, and returns back to the transceiver plane. Coherent beam scattering off the randomly rough surface results in strong speckle modulation in the transceiver plane. This speckle modulation has been a long-standing challenge that limits performance of remote sensing, active imaging, and adaptive optics techniques. Using physics-based models of laser beam scattering off a randomly rough surface, we show that received speckle-field spatial and temporal characteristics …

Recursive Non-Local Means Filter For Video Denoising, Redha A. Ali, Russell C. Hardie

Electrical and Computer Engineering Faculty Publications

In this paper, we propose a computationally efficient algorithm for video denoising that exploits temporal and spatial redundancy. The proposed method is based on non-local means (NLM). NLM methods have been applied successfully in various image denoising applications. In the single-frame NLM method, each output pixel is formed as a weighted sum of the center pixels of neighboring patches, within a given search window.

The weights are based on the patch intensity vector distances. The process requires computing vector distances for all of the patches in the search window. Direct extension of this method from 2D to 3D, for video …

High Consequence Scenarios For North Korean Atmospheric Nuclear Tests With Policy Recommendations For The U.S. Government, Thomas S. Popik, Jordan T. Kearns, George H. Baker Iii, Henry F. Cooper, William R. Harris

Department of Integrated Science and Technology - Faculty Scholarship

The government of North Korea has declared high-altitude EMP-capability to be a “strategic goal” and has also threatened an atmospheric test of a hydrogen bomb. Atmospheric nuclear tests have the potential to cripple satellites and the undersea cable networks critical to communication, and navigation necessary for trans-Pacific trade among the U.S., China, and other nations. When a nuclear warhead is detonated at high altitude, a series of electromagnetic pulses radiate downward within the line of sight of the blast. These pulses can disable equipment with miniature electronics and long conductors. Electric grid controls and transmission systems are especially vulnerable. Intense …

Analysis Of The Joint Impact Of Atmospheric Turbulence And Refractivity On Laser Beam Propagation, Victor A. Kulikov, Mikhail Vorontsov

Electro-Optics and Photonics Faculty Publications

A laser beam propagation model that accounts for the joint effect of atmospheric turbulence and refractivity is introduced and evaluated through numerical simulations. In the numerical analysis of laser beam propagation, refractive index inhomogeneities along the atmospheric propagation path were represented by a combination of the turbulence-induced random fluctuations described in the framework of classical Kolmogorov turbulence theory and large-scale refractive index variations caused by the presence of an inverse temperature layer. The results demonstrate that an inverse temperature layer located in the vicinity of a laser beam’s propagation path may strongly impact the laser beam statistical characteristics including the …

Universality Of Local Dissipation Scales In Turbulent Boundary Layer Flows With And Without Free-Stream Turbulence, Sabah F. H. Alhamdi, Sean C. C. Bailey

Mechanical Engineering Faculty Publications

Measurements of the small-scale dissipation statistics of turbulent boundary layer flows with and without free-stream turbulence are reported for Re_τ ≈ 1000 (Re_θ ≈ 2000). The scaling of the dissipation scale distribution is examined in these two boundary conditions. Results demonstrated that the local large-scale Reynolds number based on the measured longitudinal integral length scale fails to properly normalize the dissipation scale distribution near the wall in these two free-stream conditions due to the imperfect characterization of the upper bound of the inertial cascade by the integral length scale. A surrogate found from turbulent kinetic energy and …

Superconductivity At Т≈200 K In Bismuth Cuprates Synthesized Using Solar Energy, J. Chigvinadze, Juana Acrivos, S. Ashimov, D. Gulamova, G. Donadze

Faculty Publications, Chemistry

When investigating low-frequency (0.1 Hz) oscillations of multiphase high-temperature cuprate superconductors (HTCS) Bi1,7Pb0,3Sr2Ca(n-1)CunOy (n=2-30), a wide attenuation peak (ΔT~100 К) with a maximum at Т≈200 К was detected. This peak was particularly pronounced in field cooling (FC) experiments, i.e. after abrupt cooling of the sample in the external magnetic field at the temperature Т<Тс with subsequent slow warming up to room temperature with invariance of the applied field. The attenuation peak height depended on the preliminaryorientation (before cooling) of the samples θ in the measured permanent magnetic field Н. On the one hand, it is well known that, after the FC procedure and subsequent slow warming up, at the temperatures close to the critical temperature Тс, the attenuation peak associated with “melting” of the Abrikosov frozen vortex structure and its disappearance at Т >Тс is detected in monophase samples. At the same time, in most multiphase bismuth HTCS samples, synthesized using solar energy and superfast quenching of the melt, the attenuation peak with the maximum at Т≈200 К was observed.Depending on the conditions of synthesis, the attenuation peak could …

Resilient And Real-Time Control For The Optimum Management Of Hybrid Energy Storage Systems With Distributed Dynamic Demands, Christopher R. Lashway

FIU Electronic Theses and Dissertations

A continuous increase in demands from the utility grid and traction applications have steered public attention toward the integration of energy storage (ES) and hybrid ES (HESS) solutions. Modern technologies are no longer limited to batteries, but can include supercapacitors (SC) and flywheel electromechanical ES well. However, insufficient control and algorithms to monitor these devices can result in a wide range of operational issues. A modern day control platform must have a deep understanding of the source. In this dissertation, specialized modular Energy Storage Management Controllers (ESMC) were developed to interface with a variety of ES devices. The EMSC provides …

An Analysis Of The Optimal Mix Of Global Energy Resources And The Potential Need For Geoengineering Using The Ceagom Model, John George Anasis, M. A. K. Khalil, George G. Lendaris, Christopher L. Butenhoff, Randall Bluffstone

Systems Science Faculty Publications and Presentations

Humanity faces tremendous challenges as a result of anthropogenic climate change caused by greenhouse gas emissions. The mix of resources deployed in order to meet the energy needs of a growing global population is key to addressing the climate change issue. The goal of this research is to examine the optimal mix of energy resources that should be deployed to meet a forecast global energy demand while still meeting desired climate targets. The research includes the unique feature of examining the role that geoengineering can play in this optimization. The results show that some form of geoengineering is likely to …

An Enhanced Operational Definition Of Dielectric Breakdown For Dc Voltage Step-Up Tests, Allen Andersen, Jr Dennison

Journal Articles

The imprecise definition of breakdown in the ASTM D3755-14 standard can misidentify breakdown. If the recommended test circuit current sensing element threshold is set too high, breakdown may occur undetected. Conversely, false positives may result from designating a low current threshold. An operational definition of breakdown much less sensitive to these pitfalls is outlined herein. This enhanced definition of breakdown is based on the average rate of change of the leakage current with increasing voltage, rather than a simple current threshold, avoiding ambiguous association with anomalies in current traces. For tests that continuously monitor leakage current, breakdown can be detected …

Use Of A Novel Infrared Wavelength-Tunable Laser Mueller-Matrix Polarimetric Scatterometer To Measure Nanostructured Optical Materials, Jason C. Vap, Stephen E. Nauyoks, Michael R. Benson, Michael A. Marciniak

Faculty Publications

Nanostructured optical materials, for example, metamaterials, have unique spectral, directional, and polarimetric properties. Samples designed and fabricated for infrared (IR) wavelengths have been characterized using broadband instruments to measure specular polarimetric transmittance or reflectance as in ellipsometry or integrated hemisphere transmittance or reflectance. We have developed a wavelength-tunable IR Mueller-matrix (Mm) polarimetric scatterometer which uses tunable external-cavity quantum-cascade lasers (EC-QCLs) to tune onto and off of the narrowband spectral resonances of nanostructured optical materials and performed full polarimeteric and directional evaluation to more fully characterize their behavior. Using a series of EC-QCLs, the instrument is tunable over 4.37-6.54 μm wavelengths …

Spin-Imbalance In A 2d Fermi-Hubbard System, Peter Brown, Debayan Mitra, Elmer Guardado-Sanchez, Peter Schauß, Stanimir Kondov, Ehsan Khatami, Thereza Paiva, Nandini Trivedi, David Huse, Waseem Bakr

Faculty Publications

The interplay of strong interactions and magnetic fields gives rise to unusual forms of superconductivity and magnetism in quantum many-body systems. Here, we present an experimental study of the two-dimensional Fermi-Hubbard model—a paradigm for strongly correlated fermions on a lattice—in the presence of a Zeeman field and varying doping. Using site-resolved measurements, we revealed anisotropic antiferromagnetic correlations, a precursor to long-range canted order. We observed nonmonotonic behavior of the local polarization with doping for strong interactions, which we attribute to the evolution from an antiferromagnetic insulator to a metallic phase. Our results pave the way to experimentally mapping the low-temperature …

Synthesis Of Non-Uniformly Correlated Partially Coherent Sources Using A Deformable Mirror, Milo W. Hyde Iv, Santasri Bose-Pillai, Ryan A. Wood

Faculty Publications

The near real-time synthesis of a non-uniformly correlated partially coherent source using a low-actuator-count deformable mirror is demonstrated. The statistical optics theory underpinning the synthesis method is reviewed. The experimental results of a non-uniformly correlated source are presented and compared to theoretical predictions. A discussion on how deformable mirror characteristics such as actuator count and pitch affect source generation is also included.

Interplay Of Quantum Size Effect, Anisotropy And Surface Stress Shapes The Instability Of Thin Metal Films, Mikhail Khenner

Mathematics Faculty Publications

Morphological instability of a planar surface ([111], [011], or [001]) of an ultra-thin metal film is studied in a parameter space formed by three major effects (the quantum size effect, the surface energy anisotropy and the surface stress) that influence a film dewetting. The analysis is based on the extended Mullins equation, where the effects are cast as functions of the film thickness. The formulation of the quantum size effect (Z. Zhang et al., PRL 80, 5381 (1998)) includes the oscillation of the surface energy with thickness caused by electrons confinement. By systematically comparing the effects, their contributions into the …

A Mathematical Model And Numerical Simulations Of Redox Electrochemical Systems With Mhd And Natural Convection, Kakkattukuzhy M. Isaac, Fangping Yuan

Collaborative Research: Actively Controllable Microfluidics with Film-Confined Redox-Magnetohydrodynamics -- Video and Data

A comprehensive mathematical model for redox electrochemical systems with magnetohydrodynamics (MHD) and natural convection are presented. The model is based on density changes in isothermal systems that accompany redox reaction at the electrode due to supporting electrolyte ions migrating into and out of the diffusion layer to satisfy electroneutrality. Numerical simulations have been performed for an axisymmetric, milli-electrode electrochemical cell with gravity directed along the axis in both directions to investigate the effect of the electrode orientation with respect to gravity. Results show that natural convection is significant in both cases, with the maximum velocity being an order of magnitude …

On-Chip, High-Sensitivity Temperature Sensors Based On Dye-Doped Solid-State Polymer Microring Lasers, Lei Wan, Hengky Chandrahalim, Cong Chen, Qiushu Chen, Ting Mei, Yuji Oki, Naoya Nishimura, Lingjie Jay Guo, Xudong Fan

Faculty Publications

We developed a chip-scale temperature sensor with a high sensitivity of 228.6 pm/°C based on a rhodamine 6G (R6G)-doped SU-8 whispering-gallery mode microring laser. The optical mode was largely distributed in a polymer core layer with a 30 μm height that provided detection sensitivity, and the chemically robust fused-silica microring resonator host platform guaranteed its versatility for investigating different functional polymer materials with different refractive indices. As a proof of concept, a dye-doped hyperbranched polymer (TZ-001) microring laser-based temperature sensor was simultaneously developed on the same host wafer and characterized using a free-space optics measurement setup. Compared to TZ-001, the …

Electrical Characterization Of Irradiated Semiconducting Amorphous Hydrogenated Boron Carbide, George Glen Peterson

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Semiconducting amorphous partially dehydrogenated boron carbide has been explored as a neutron voltaic for operation in radiation harsh environments, such as on deep space satellites/probes. A neutron voltaic device could also be used as a solid state neutron radiation detector to provide immediate alerts for radiation workers/students, as opposed to the passive dosimetry badges utilized today. Understanding how the irradiation environment effects the electrical properties of semiconducting amorphous partially dehydrogenated boron carbide is important to predicting the stability of these devices in operation. p-n heterojunction diodes were formed from the synthesis of semiconducting amorphous partially dehydrogenated boron carbide on silicon …

On-Chip Training Of Memristor Crossbar Based Multi-Layer Neural Networks, Raqibul Hasan, Tarek M. Taha, Christopher Yakopcic

Electrical and Computer Engineering Faculty Publications

Memristor crossbar arrays carry out multiply-add operations in parallel in the analog domain, and so can enable neuromorphic systems with high throughput at low energy and area consumption. On-chip training of these systems have the significant advantage of being able to get around device variability and faults. This paper presents on-chip training circuits for multi-layer neural networks implemented using a single crossbar per layer and two memristors per synapse. Using two memristors per synapse provides double the synaptic weight precision when compared to a design that uses only one memristor per synapse. Proposed on-chip training system utilizes the back propagation …

Nanostructure Evolution Of Magnetron Sputtered Hydrogenated Silicon Thin Films, Dipendra Adhikari, Maxwell M. Junda, Sylvain X. Marsillac, Robert W. Collins, Nikolas J. Podraza

Electrical & Computer Engineering Faculty Publications

Hydrogenated silicon (Si:H) thin films have been prepared by radio frequency (RF) magnetron sputtering. The effect of hydrogen gas concentration during sputtering on the resultant film structural and optical properties has been investigated by real time spectroscopic ellipsometry (RTSE) and grazing incidence x-ray diffraction (GIXRD). The analysis of in-situ RTSE data collected during sputter deposition tracks the evolution of surface roughness and film bulk layer thickness with time. Growth evolution diagrams depicting amorphous, nanocrystalline and mixed-phase regions for low and high deposition rate Si:H are constructed and the effects of process parameter (hydrogen gas concentration, total pressure and RF power) …

Electron Paramagnetic Resonance Study Of Neutral Mg Acceptors In Β-Ga2O3 Crystals, Brant E. Kananen, Larry E. Halliburton, Elizabeth M. Scherrer, K. T. Stevens, G. K. Foundos, K. B. Chang, Nancy C. Giles

Faculty Publications

Electron paramagnetic resonance (EPR) is used to directly observe and characterize neutral Mg acceptors (Mg⁰_Ga) in a β-Ga₂O₃ crystal. These acceptors, best considered as small polarons, are produced when the Mg-doped crystal is irradiated at or near 77 K with x rays. During the irradiation, neutral acceptors are formed when holes are trapped at singly ionized Mg acceptors (Mg−Ga). Unintentionally present Fe³⁺ (3d⁵) and Cr³⁺ (3d³) transition-metal ions serve as the corresponding electron traps. The hole is localized in a nonbonding p orbital on a threefold-coordinated oxygen ion …

Suppression Of Magnetism In Ba5Alir2O11: Interplay Of Hund's Coupling, Molecular Orbitals, And Spin-Orbit Interaction, Sergey V. Streltsov, Gang Cao, Daniel I. Khomskii

Center for Advanced Materials Faculty Publications

The electronic and magnetic properties of Ba₅AlIr₂O₁₁ containing Ir-Ir dimers are investigated using the generalized gradient approximation (GGA) and GGA + spin-orbit coupling (SOC) calculations. We found that the strong suppression of the magnetic moment in this compound recently found by Terzic et al. [Phys. Rev. B 91, 235147 (2015)] is not due to charge ordering but is related to the joint effect of the spin-orbit interaction and strong covalency, resulting in the formation of metal-metal bonds. They conspire and act against the intraatomic Hund's rule exchange interaction to reduce total magnetic moment of the …

Band Offsets At The Interface Between Crystalline And Amorphous Silicon From First Principles, Karol Jarolimek, E. Hazrati, R. A. De Groot, D. A. De Wijs

Center for Applied Energy Research Faculty and Staff Publications

The band offsets between crystalline and hydrogenated amorphous silicon (a−Si∶H) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature …

Real-Time Camera Tracking System Using Optical Flow Feature Points, Daniel D. Doyle, Alan L. Jennings, Jonathan T. Black

AFIT Patents

A new apparatus and method for tracking a moving object with a moving camera provides a real-time, narrow field-of-view, high resolution and on target image by combining commanded motion with an optical flow algorithm for deriving motion and classifying background. Commanded motion means that movement of the pan, tilt and zoom (PTZ) unit is “commanded” by a computer, instead of being observed by the camera, so that the pan, tilt and zoom parameters are known, as opposed to having to be determined, significantly reducing the computational requirements for tracking a moving object. The present invention provides a single camera pan …

Broadband Acoustic Measurement Of The Agar-Based Tissue Mimicking Material – A Longitudinal Study, Adela Rabell-Montiel, Jacinta Browne, Stephen Pye, Tom Anderson, Carmel Moran

Articles

Commercially available ultrasound quality assurance test phantoms rely upon the long-term acoustic stability of tissue-mimicking-materials (TMMs). The measurement of the acoustic properties can be technically challenging and it is important to ensure its stability. The standard technique is to film-wrap samples of TMM and to measure the acoustic properties in a water bath. In this study, a modified technique is proposed whereby the samples of TMM are measured in a preserving fluid that is intended to maintain their characteristics. The acoustic properties were evaluated using a broadband pulse-echo substitution technique over the frequency range of 4.5 – 50 MHz at …

Elastic Properties Of Superconductors And Materials With Weakly Correlated Spins, Christian Binek

Christian Binek Publications

It is shown that in the ergodic regime, the temperature dependence of Young’s modulus is solely determined by the magnetic properties of a material. For the large class of materials with paramagnetic or diamagnetic response, simple functional forms of the temperature derivative of Young’s modulus are derived and compared with experimental data and empirical results. Superconducting materials in the Meissner phase are ideal diamagnets. As such, they display remarkable elastic properties. Constant diamagnetic susceptibility gives rise to a temperature independent elastic modulus for ceramic and single crystalline superconductors alike. The thermodynamic approach established in this report, paves the way to …

Perspective: The Physics, Diagnostics, And Applications Of Atmospheric Pressure Low Temperature Plasma Sources Used In Plasma Medicine, M. Laroussi

Electrical & Computer Engineering Faculty Publications

Low temperature plasmas have been used in various plasma processing applications for several decades. But it is only in the last thirty years or so that sources generating such plasmas at atmospheric pressure in reliable and stable ways have become more prevalent. First, in the late 1980s, the dielectric barrier discharge was used to generate relatively large volume diffuse plasmas at atmospheric pressure. Then, in the early 2000s, plasma jets that can launch cold plasma plumes in ambient air were developed. Extensive experimental and modeling work was carried out on both methods and much of the physics governing such sources …

Describing And Mapping The Interactions Between Student Affective Factors Related To Persistence In Science, Physics, And Engineering, Jacqueline Doyle

FIU Electronic Theses and Dissertations

This dissertation explores how students’ beliefs and attitudes interact with their identities as physics people, motivated by calls to increase participation in science, technology, engineering, and mathematics (STEM) careers. This work combines several theoretical frameworks, including Identity theory, Future Time Perspective theory, and other personality traits to investigate associations between these factors. An enriched understanding of how these attitudinal factors are associated with each other extends prior models of identity and link theoretical frameworks used in psychological and educational research. The research uses a series of quantitative and qualitative methodologies, including linear and logistic regression analysis, thematic interview analysis, and …

Ionic Thermoelectric Paper, Fei Jiao, Ali Naderi, Dan Zhao, Joshua Schlueter, Maryam Shahi, Jonas Sundström, Hjalmar Granberg, Jesper Edberg, Ujwala Ail, Joseph W. Brill, Tom Lindström, Magnus Berggren, Xavier Crispin

Physics and Astronomy Faculty Publications

Ionic thermoelectric materials, for example, polyelectrolytes such as polystyrene sulfonate sodium (PSSNa), constitute a new class of materials which are attracting interest because of their large Seebeck coefficient and the possibility that they could be used in ionic thermoelectric SCs (ITESCs) and field effect transistors. However, pure polyelectrolyte membranes are not robust or flexible. In this paper, the preparation of ionic thermoelectric paper using a simple, scalable and cost-effective method is described. After a composite was fabricated with nanofibrillated cellulose (NFC), the resulting NFC–PSSNa paper is flexible and mechanically robust, which is desirable if it is to be used in …

The Magnetic, Electrical And Structural Properties Of Copper-Permalloy Alloys, Makram A. Qader, A. Vishina, Lei Yu, Cougar Garcia, Rakesh K. Singh, Nicholas D. Rizzo, Mengchu Huang, Ralph Chamberlin, Kirill Belashchenko, Mark Van Schilfgaarde, N. Newman

Kirill Belashchenko Publications

Copper-permalloy [Cu_1–x(Ni₈₀Fe₂₀)_x] alloy films were deposited by co-sputtering and their chemical, structural, magnetic, and electrical properties were characterized. These films are found to have favorable weak ferromagnetic properties for low temperature magnetoelectronic applications. Our results show that by varying the composition, the saturation magnetization (M_s) can be tuned from 700 emu/cm³ to 0 and the Curie temperature (T_c), can be adjusted from 900 K to 0 K. The M_s and T_c are found to scale linearly between x = 25% and 100%. Electronic structure calculations …