Engineering Commons^™

Assessing Postural Stability Via The Correlation Patterns Of Vertical Ground Reaction Force Components, Chih-Yuan Hong, Lan-Yuen Guo, Rong Song, Mark L. Nagurka, Jia-Li Sung, Chen-Wen Yen

Mechanical Engineering Faculty Research and Publications

Background

Many methods have been proposed to assess the stability of human postural balance by using a force plate. While most of these approaches characterize postural stability by extracting features from the trajectory of the center of pressure (COP), this work develops stability measures derived from components of the ground reaction force (GRF).

Methods

In comparison with previous GRF-based approaches that extract stability features from the GRF resultant force, this study proposes three feature sets derived from the correlation patterns among the vertical GRF (VGRF) components. The first and second feature sets quantitatively assess the strength and changing speed of …

Transient Analysis Of Lumped Circuit Networks-Loaded Thin Wires By Dgtd Method, P. Li, Y. Shi, Lijun Jiang, H. Bagci

Electrical and Computer Engineering Faculty Research & Creative Works

With the purpose of avoiding very fine mesh cells in the proximity of a thin wire, the modified telegrapher’s equations (MTEs) are employed to describe the thin wire voltage and current distributions, which consequently results in reduced number of unknowns and augmented Courant–Friedrichs–Lewy (CFL) number. As hyperbolic systems, both the MTEs and the Maxwell’s equations are solved by the discontinuous Galerkin time-domain (DGTD) method. In realistic situations, the thin wires could be either driven or loaded by circuit networks. The thin wire–circuit interface performs as a boundary condition for the thin wire solver, where the thin wire voltage and current …

A Verified Information-Flow Architecture, Arthur Azevedo De Amorim, Nathan Collins, André Dehon, Delphine Demange, Cătălin Hriţcu, David Pichardie, Benjamin C. Pierce, Randy Pollack, Andrew Tolmach

Computer Science Faculty Publications and Presentations

SAFE is a clean-slate design for a highly secure computer system, with pervasive mechanisms for tracking and limiting information flows. At the lowest level, the SAFE hardware supports fine-grained programmable tags, with efficient and flexible propagation and combination of tags as instructions are executed. The operating system virtualizes these generic facilities to present an information-flow abstract machine that allows user programs to label sensitive data with rich confidentiality policies. We present a formal, machine-checked model of the key hardware and software mechanisms used to dynamically control information flow in SAFE and an end-to-end proof of noninterference for this model. We …

A Comprehensive Model Of The Transport Phenomena In Gas Metal Arc Welding, Junling Hu, Zhenghua Rao, Hai-Lung Tsai

Mechanical and Aerospace Engineering Faculty Research & Creative Works

A comprehensive two-dimensional gas metal arc welding (GMAW) model was developed to take into account all the interactive events in the gas metal arc welding process, including the arc plasma, melting of the electrode, droplet formation, detachment, transfer, and impingement onto the workpiece, and the weld-pool dynamics and weld formation. The comprehensive GMAW model tracks the free surface using the volume of fluid method and directly modeled the coupling effects between the arc domain and the metal domain, thus eliminating the need to assign boundary conditions at the interface. A thorough investigation of the plasma arc characteristics was conducted to …

Geometric Consideration Of Nanostructures For Energy Storage Systems, Jonghyun Park, Jie Li, Wei Lu, Ann Marie Sastry

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Battery performance and its fade are determined by various aspects such as the transport of ions and electrons through heterogeneous internal structures; kinetic reactions at the interfaces; and the corresponding interplay between mechanical, chemical, and thermal responses. The fundamental factor determining this complex multiscale and multiphysical nature of a battery is the geometry of active materials. In this work, we systematically consider the tradeoffs among a selection of limiting geometries of media designed to store ions or other species via a diffusion process. Specifically, we begin the investigation by considering diffusion in spheres, rods, and plates at the particle level, …

Ionic And Electronic Conductivities Of Atomic Layer Deposition Thin Film Coated Lithium Ion Battery Cathode Particles, Rajankumar L. Patel, Jonghyun Park, Xinhua Liang

Mechanical and Aerospace Engineering Faculty Research & Creative Works

It is imperative to ascertain the ionic and electronic components of the total conductivity of an electrochemically active material. A blocking technique, called the “Hebb-Wagner method”, is normally used to explain the two components (ionic and electronic) of a mixed conductor, in combination with the complex ac impedance method and dc polarization measurements. CeO₂ atomic layer deposition (ALD)-coated and uncoated, LiMn₂O₄ (LMO) and LiMn_1.5Ni_0.5O₄ (LMNO) powders were pressed into pellets and then painted with silver to act as a blocking electrode. The electronic conductivities were derived from the currents obtained using …

Silicon-Wall Interfacial Free Energy Via Thermodynamics Integration, Wan Shou, Heng Pan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

We compute the interfacial free energy of a silicon system in contact with flat and structured walls by molecular dynamics simulation. The thermodynamics integration method, previously applied to Lennard-Jones potentials [R. Benjamin and J. Horbach, J. Chem. Phys. 137, 044707 (2012)], has been extended and implemented in Tersoff potentials with two-body and three-body interactions taken into consideration. The thermodynamic integration scheme includes two steps. In the first step, the bulk Tersoff system is reversibly transformed to a state where it interacts with a structureless flat wall, and in a second step, the flat structureless wall is reversibly transformed into an …

A Novel Relaxed Hierarchical Equivalent Source Algorithm (Rhesa) For Electromagnetic Scattering Analysis Of Dielectric Objects, Xin Fu, Li (Lijun) Jun Jiang, Hong Tat Ewe

Electrical and Computer Engineering Faculty Research & Creative Works

A novel relaxed hierarchical algorithm based on the surface equivalence principle for the volume integral equations (VIEs) is proposed in this work. The equivalent sources residing on relaxed spherical equivalence surfaces are established by exact integral formulations. The equivalence surfaces are exploited hierarchically to accelerate matrix–vector product in iterative solutions for the VIEs. The computation time and memory cost complexity of the proposed algorithm for dielectric scatters scale as O(N4/3) and O(N) , respectively. Numerical examples validate the accuracy and capability of the proposed algorithm.

Performance Enhancement Of Equivalence Principle Algorithm, Xin Fu, Li (Lijun) Jun Jiang, Zu Hui Ma, Shi Quan He

Electrical and Computer Engineering Faculty Research & Creative Works

The conventional equivalence principle algorithm (EPA) exploits cubical surfaces to support equivalent sources. However, it introduces strong discontinuities due to sharp edges and corners. In this letter, a spherical surface is employed as the equivalence surface to avoid singularities from nonsmoothness. To achieve better accuracy, the meshless sampling scheme is used for integral operators on the spherical equivalence surface. The numerical examples are provided to validate the performance enhancement of EPA through the proposed method.

The Coupled Photothermal Reaction And Transport In A Laser Additive Metal Nanolayer Simultaneous Synthesis And Patterning For Flexible Electronics, S. Tsai, Y. Liu, Heng Pan, C. Liu, M. Lee

Mechanical and Aerospace Engineering Faculty Research & Creative Works

No abstract provided.

Output Feedback Adaptive Control With Low-Frequency Learning And Fast Adaptation, Tanmay Rajpurohit, Wassim M. Haddad, Tansel Yucelen

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Although adaptive control has been used in numerous applications to achieve system performance without excessive reliance on system models, the necessity of high-gain learning rates for achieving fast adaptation can be a serious limitation of adaptive controllers. Specifically, in safety-critical systems involving large system uncertainties and abrupt changes in system dynamics, fast adaptation is required to achieve stringent tracking performance specifications. However, fast adaptation using high-gain learning rates can cause high-frequency oscillations in the control response, resulting in system instability. This paper develops an output feedback adaptive control framework for continuous-time minimum-phase multivariable dynamical systems for output stabilization and command …

Observation Of Late-Time Ablation In Electric Solid Propellant Pulsed Microthrusters, Matthew S. Glascock, Joshua L. Rovey, Shae Williams, Jason Thrasher

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Electric solid propellants are an interesting potential option for propulsion because they are ignited by an applied electric current. The electric nature of these materials leads to the capability for use in pulsed electric propulsion devices. In this work, the ablation process of an electric solid propellant during pulsed micro thruster operation is investigated using a triple Langmuir probe, thrust stand and high-speed video camera. Results include quantitative time-of-flight, ablation mass per pulse and impulse-per-pulse measurements. Additionally, qualitative images from the high-speed video are temporally correlated to these measurements. Analyses indicate 45±11% of the ablated mass per pulse is expelled …

Mass Spectrometry Of Selected Ionic Liquids In Capillary Electrospray At Nanoliter Volumetric Flow Rates, Shawn W. Miller, Benjamin D. Prince, Raymond J. Bemish, Joshua L. Rovey

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Capillary-based electrospray thrusters allow user-enabled control of the volumetric flow rate of the propellant. This control, coupled with mass spectrometry techniques spanning a large mass-to-charge range, enables elucidation of the composition of the electrospray beam and through further analyses, a better understanding of the physics occurring at the liquid/vacuum interface. In this work, mass spectra of selected ionic liquids electro sprayed from a capillary emitter are measured, using time-of-flight mass spectrometry, over a wide range of volumetric flow rates. The time-of-flight mass spectrometer enables simultaneous acquisition over a mass-to-charge range of 20 amu/q to ~500,000 amu/q in a single pulse …

Comparison Of Robust And Probabilistic Lmi-Based Design Of Adaptive Flight Controllers With Uncertain Input Dynamics, Mario Luca Fravolini, Tansel Yucelen, Benjamin Gruenwald, Merve Dogan, Marcello R. Napolitano

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Adaptive control-based schemes have been implemented to date in a variety of different ap-plications. However, the ability to obtain a predictable transient closed-loop performance in adaptive systems is still a challenging problem from a verification and validation point of view. To face this problem we have recently introduced an analysis and design framework for adaptive control systems in the presence of bounded uncertainty and bounded adaptive control (the boundedness can be enforced, for instance, by a parameter projection mechanism) showing that the transitory performance of a MRAC system can be expressed, analyzed, and optimized via a convex optimization formulation based …

Stress-Induced Birefringence And Fabrication Of In-Fiber Polarization Devices By Controlled Femtosecond Laser Irradiations, Lei Yuan, Baokai Cheng, Jie Huang, Jie Liu, Hanzheng Wang, Xinwei Lan, Hai Xiao

Electrical and Computer Engineering Faculty Research & Creative Works

Optical birefringence was created in a single-mode fiber by introducing a series of symmetric cuboid stress rods on both sides of the fiber core along the fiber axis using a femtosecond laser. The stress-induced birefringence was estimated to be 2.4 x 10^-4 at the wavelength of 1550 nm. By adding the desired numbers of stressed rods, an in-fiber quarter waveplate was fabricated with a insertion loss of 0.19 dB. The stressinduced birefringence was further explored to fabricate in-fiber polarizers based on the polarization-dependent long-period fiber grating (LPFG) structure. A polarization extinction ratio of more than 20 dB was observed …

Co-Doping Of Magnesium With Indium In Nitrides: First Principle Calculation And Experiment, Zhiqiang Liu, Binglei Fu, Xiaoyan Yi, Guodong Yuan, Junxi Wang, Jinmin Li, Luna, Ian Ferguson

Electrical and Computer Engineering Faculty Research & Creative Works

In this work, an effective strategy for achieving efficient p-type doping in wide bandgap nitride semiconductors was proposed to overcome the fundamental issue of high activation energy. We demonstrated that a hole concentration as high as 1.4 x 1018 cm-3 could been achieved through In-Mg co-doping. The electronic structure of the system and the formation energy of impurity were analyzed via first principal calculation to clarify the underlying physics and the ambiguity in understanding of the origin of the high hole concentration. Our results indicated that the original valence band maximum of the host materials could be modified, thus improving …

Efficient Modeling And Simulation Of Wavelength Division Multiplexing Dual Polarization Qpsk Optical Fiber Transmission, Siva Kumar Raju Nadimpalli

All Graduate Theses, Dissertations, and Other Capstone Projects

Due to enormous growth in communications, wavelength division multiplexing (WDM) systems are popular because these systems allow us to expand the capacity of the networks without laying more optical fiber cables. In this thesis, we have systematically derived the coupled nonlinear Schrödinger (CNLS) equations, including a consistent definition of the complex envelope, Fourier transform, the state of polarization, and derivation under the engineering notation. After a discussion of coarse step based second order symmetrized split-step Fourier (SSSF) simulation method, which is applicable to the numerical solution of the CNLS equations, an analytical step-size selection based local error method is applied …

The Concept Of Substrate Integrated E-Plane Waveguide And Circuits, Danyang Huang

All Graduate Theses, Dissertations, and Other Capstone Projects

In this thesis, a new type of substrate integrated waveguide is proposed for implementing E-plane type of waveguide circuits on printed circuit boards. obviously, these E-plane type of circuits cannot be realized by the conventional substrate integrated waveguide. The so-called substrate integrated E-plane waveguide consists of two circuit boards attached to each other. Two copper strips are inserted in between two circuit boards, where plated through holes are penetrated through them along the transmission direction. The plated through holes and copper strips altogether played as side walls of a conventional waveguide to support longitudinal and vertical currents. Simulation is carried …

A 2x2 Polarization Switchable Patch Antenna Array For Polarization Modulation, Pengfei Ji

All Graduate Theses, Dissertations, and Other Capstone Projects

This thesis introduced and investigated a new concept in the development of a 2X2 polarization switchable patch antenna array for polarization modulation. Polarization modulation is a technique to modulate digital information using different polarization of the electromagnetic wave. The existing waveform based modulation techniques are well developed and start approaching to their performance limits. Polarization modulation provides a new modulation dimension for wireless communications and can further increase data throughput. A four-port circular patch antenna is presented and investigated for the implementation of polarization modulation. It has four ports, each excites radiation of a different polarization. A single pole four …

Effects Of Computer Program Visualization Tools On Student Populations, Meghan Jayne Peterson

All Graduate Theses, Dissertations, and Other Capstone Projects

This study examined how program visualization tools affect Advanced Placement Computer Science students' understanding of abstract programming concepts. A literature review was conducted to determine if program visualization is effective and which students benefit from it the most. The findings were used to design a causal comparative study in which students would experience instruction with and without program visualization. The study took place in an AP Computer Science course during the first challenging unit about an abstract concept: loops. Participants (n = 24) were selected using convenience sampling and were assessed before, during, and after the study took place. While …

Nebraska Summary: S1077 New Holland T7.245, Nebraska Tractor Test Lab

Nebraska Tractor Tests

ABOUT THE TEST REPORT AND USE OF THE DATA The test data contained in this report are a tabulation of the results of a series of tests. Due to the restricted format of these pages, only a limited amount of data and not all of the tractor specifications are included. The full OECD report contains usually about 30 pages of data and specifications. The test data were obtained for each tractor under similar conditions and therefore, provide a means of comparison of performance based on a limited set of reported data. EXPLANATION OF THE TEST PROCEDURES Purpose The purpose of …

Nebraska Summary: S1101 New Holland T6.175, Nebraska Tractor Test Lab

Nebraska Tractor Tests

ABOUT THE TEST REPORT AND USE OF THE DATA The test data contained in this report are a tabulation of the results of a series of tests. Due to the restricted format of these pages, only a limited amount of data and not all of the tractor specifications are included. The full OECD report contains usually about 30 pages of data and specifications. The test data were obtained for each tractor under similar conditions and therefore, provide a means of comparison of performance based on a limited set of reported data. EXPLANATION OF THE TEST PROCEDURES Purpose The purpose of …

Monitoring Voip Speech Quality For Chopped And Clipped Speech, Andrew Hines, Jan Skoglund, Anil C. Kokaram, Naomi Harte

Articles

No abstract provided.

Comparison Of Ignition Delays And Liquid Penetrations Of Jp-8, Synthetic Jp-8, And A Jp-8 Surrogate Under Diesel Engine Conditions, Kyle Yeakle

Dissertations, Master's Theses and Master's Reports

The U.S. Army and many NATO affiliates have adopted a ‘one fuel forward fuel policy’ (OFF). The goal of the OFF policy is reducing the logistics and cost involved with providing fuel for military vehicles. With this policy, the logical choice fuel is military grade jet petroleum, JP-8, because of the fuel constraints of turbo-jet engines. This requirement has made it necessary to run military compression ignited engines on JP-8. To reduce the Army’s reliance on petroleum based fuels an alternative fuel, synthetic JP-8, derived from coal and made in the Fischer-Tropsch production method is allowed to be blended up …

Polychlorinated Biphenyl Compound And Metal Contamination And Remediation In Torch Lake, Houghton County, Mi, Ankita Mandelia

Dissertations, Master's Theses and Master's Reports

Torch Lake was subject to approximately 100 years of industrial pollution due to the dumping of waste associated with copper mining in the Keweenaw Peninsula, which lasted from approximately the 1860s through the 1960s. It is well-known that this waste included copper-containing mine tailings. What was less understood are the impacts of polychlorinated biphenyls (PCBs) and heavy metals besides copper on the lake system.

The objectives of this thesis are to summarize the status of contamination and remediation activities in Torch Lake and to estimate the magnitude of potential sources of PCBs to Torch Lake. First, a brief overview of …

Increasing Solar Energy Conversion Efficiency In Hydrogenated Amorphous Silicon Photovoltaic Devices With Plasmonic Perfect Meta – Absorbers, Jephias Gwamuri

Dissertations, Master's Theses and Master's Reports

Solar photovoltaic (PV) devices are an established, technically-viable and sustainable solution to society’s energy needs, however, in order to reach mass deployment at the terawatt scale, further decreases in the levelized cost of electricity from solar are needed. This can be accomplished with thin-film PV technologies by increasing the conversion efficiency using sophisticated light management methods. This ensures absorption of the entire solar spectrum, while reducing semiconductor absorber layer thicknesses, which reduces deposition time, material use, embodied energy and greenhouse gas emissions, and economic costs. Recent advances in optics, particularly in plasmonics and nanophotonics provide new theoretical methods to improve …

Experimental Study, Modelling And Controller Design For An Rcci Engine, Naga Nithin Teja Kondipati

Dissertations, Master's Theses and Master's Reports

Low Temperature Combustion (LTC) has got widespread attention over the past two decades in the field of Automotive Research and Development due to it’s potential for achieving higher efficiencies with near-zero engine out NOx and soot emissions. Among all the LTC strategies Reactivity controlled compression ignition (RCCI) has shown the most promising results due to it’s precise control over combustion phasing and heat release rate. However, RCCI being a dual-fuel stratified combustion, precise control over the injection timing of direct injected fuel and in-cylinder fuel reactivity of the mixture needs to be controlled effectively in order to achieve gross indicated …

Dynamic Atomistic Study Of Tunnel Functions In Nanostructured Transitional Metal Oxides, Yifei Yuan

Dissertations, Master's Theses and Master's Reports

Alpha (α-) MnO₂ is a well know transitional metal oxide possessing one dimensional 2×2 (4.6 × 4.6 Ų) tunnels for accommodation of various ions. Such a characteristic tunneled structure has enabled the wide applications of α-MnO₂ in the fields of ion exchange, molecular sieves, biosensor, catalysis and energy storage. This PhD dissertation focuses on the dynamic study of ion transport functionality of α-MnO₂ at atomic level using an aberration corrected scanning transmission electron microscopy equipped with a special holder with a scanning tunneling microscopy probe.

The wide application of in situ TEM studying the dynamic …

Thermomechanical Processing Of Aluminum Micro-Alloyed With Sc, Zr, Ti, B, And C, Cameron Mcnamara

Dissertations, Master's Theses and Master's Reports

Critical exploration of the minimalistic high strength low alloy aluminum (HSLA-Al) paradigm is necessary for the continued development of advanced aluminum alloys. In this study, scandium (Sc) and zirconium (Zr) are examined as the main precipitation strengthening additions, while magnesium (Mg) is added to probe the synergistic effects of solution and precipitation hardening, as well as the grain refinement during solidification afforded by a moderate growth restriction factor. Further, pathways of recrystallization are explored in several potential HSLA-Al systems sans Sc. Aluminum-titanium-boron (Al-Ti-B) and aluminum-titanium-carbon (Al-Ti-C) grain refining master alloys are added to a series of Al-Zr alloys to examine …

Property Analysis Of The Asphalt Materials Using Molecular Dynamics (Md) Method, Hui Yao

Dissertations, Master's Theses and Master's Reports

The main objectives of this dissertation are to build the Molecular Dynamics (MD) model for the asphalt binders with three components, asphaltenes, aromatics and saturates, and analyze the properties of the asphalt models to discover the interactions and mechanisms of asphalt-aggregate and asphalt-modifier. The contributions of this dissertation are summarized as follows: (1) the Amber Cornell Extension Force Field (ACEFF) was assigned to each component, and most of the parameters of the force field were obtained from the General Amber Force Field (GAFF). Electrostatic Potential (ESP) charges were assigned to each atom with the NWChem calculation; (2) the modified asphalt …