Engineering Commons^™

Design Of Lattice Structures With Graded Density Fabricated By Additive Manufacturing, Wenjin Tao, Yong Liu, Austin T. Sutton, Krishna C. R. Kolan, Ming-Chuan Leu

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Lattice structures fabricated by Additive Manufacturing (AM) processes are promising for many applications, such as lightweight structures and energy absorbers. However, predicting and controlling of their mechanical behaviors is challenging due to the complexity of modeling and the uncertainties exist in the manufacturing process. In this paper, we explore the possibilities enabled by controlling the local densities. A set of lattice structures with different density gradients are designed using an implicit isosurface equation, and they are manufactured by Selective Laser Melting (SLM) process with 304L stainless steel. Finite element analysis and compression test are used to evaluate their mechanical properties. …

Rates Of Cavity Filling By Liquids, Dongjin Seo, Alex M. Schrader, Szu-Ying Chen, Yair Kaufman, Thomas R. Cristiani, Steven H. Page, Peter H. Koenig, Yonas Gizaw, Dong Woog Lee, Jacob N. Israelachvili

Faculty Publications

Understanding the fundamental wetting behavior of liquids on surfaces with pores or cavities provides insights into the wetting phenomena associated with rough or patterned surfaces, such as skin and fabrics, as well as the development of everyday products such as ointments and paints, and industrial applications such as enhanced oil recovery and pitting during chemical mechanical polishing. We have studied, both experimentally and theoretically, the dynamics of the transitions from the unfilled/partially filled (Cassie–Baxter) wetting state to the fully filled (Wenzel) wetting state on intrinsically hydrophilic surfaces (intrinsic water contact angle < 90°, where the Wenzel state is always the thermodynamically favorable state, while a temporary metastable Cassie–Baxter state can also exist) to determine the variables that control the rates of such transitions. We prepared silicon wafers with cylindrical cavities of different geometries and immersed them in bulk water. With bright-field and confocal fluorescence microscopy, we observed the details of, and the rates associated with, water penetration into the cavities from the bulk. We find that unconnected, reentrant cavities (i.e., cavities that open up below the surface) have the slowest cavity-filling rates, while connected or non-reentrant cavities undergo very rapid transitions. Using these unconnected, reentrant cavities, we identified the variables that affect cavity-filling rates: (i) the intrinsic contact angle, (ii) …

U.S. Government Aviation Safety Information Resources, Bert Chapman

Libraries Faculty and Staff Presentations

Presentation covering U.S. Government aviation safety information resources. Topics addressed include U.S. laws,legislation, regulations, court cases, information resources from agencies such as the Federal Aviation Administration, Transportation Security Administration, National Aeronautics and Space Administration, congressional aviation oversight committees and congressional support agencies including the Congressional Budget Office, Congressional Research Service, and Government Accountability Office.

Cyclists' Queue Discharge Characteristics At Signalized Intersections, Kirk Thomas Paulsen

Dissertations and Theses

Wider bike facilities intuitively accommodate a greater number of cyclists in the same amount of time, but specific queue discharge characteristics associated with varying widths and/or types of bike facilities have not been thoroughly documented.

The focus of this research analyzed queues of cyclists at four signalized intersections in Portland, OR with varying widths on the approach and downstream intersection legs. A total of 2,820 cyclists within 630 groups of queued cyclists were observed at five different intersection layouts in Portland, Oregon. The layouts consisted of: a standard bike lane six feet wide connecting bicyclists to a standard bike lane …

Whole Cell Cross-Linking To Discover Host-Microbe Protein Cognate Receptor/Ligand Pairs, Bart C. Weimer, Poyin Chen, Prerak T. Desai, Dong Chen, Jigna Shah

Biological Engineering Faculty Publications

Bacterial surface ligands mediate interactions with the host cell during association that determines the specific outcome for the host–microbe association. The association begins with receptors on the host cell binding ligands on the microbial cell to form a partnership that initiates responses in both cells. Methods to determine the specific cognate partnerships are lacking. Determining these molecular interactions between the host and microbial surfaces are difficult, yet crucial in defining biologically important events that are triggered during association of the microbiome, and critical in defining the initiating signal from the host membrane that results in pathology or commensal association. In …

Retrieval Of Infotainment System Artifacts From Vehicles Using Ive, Celia J. Whelan, John Sammons, Brian Mcmanus, Terry W. Fenger

Journal of Applied Digital Evidence

The analysis of mobile devices and hard drives has been the focus of the digital forensics world for years, but there is another source of potential evidence not often considered: vehicles. Many of today’s “connected cars” have systems that function like computers, storing information they process including user data from devices synced to the system. There has been little to no research done regarding what types of user artifacts can be found on the system, how long these artifacts remain, whether or not the user can remove those artifacts, and whether certain systems provide more information than others. For this …

Effect Of Cyclic Loading On Hydrogen Diffusion In Low Carbon Steels, Diego Pesenti Bucella, Lorenzi S, Pastore T, Cabrini M.

Stress-Assisted Corrosion Damage V

Carbon steels or low-alloyed steels may be affected by damaging phenomena due to Hydrogen Embrittlement (HE), which is a particular form of Environmental Assisted Cracking (EAC). The insurgence of HE depends on the intrinsic susceptibility of the steel, the applied stress, and the concentration of hydrogen inside the metal. It occurs by a mechanism of absorption and subsequent diffusion of atomic hydrogen through the metal lattice.

On steels with a yield strength lower than 700 MPa, HE occurs in the plastic deformation field, in the presence of dynamic loading at slow strain rates or cyclic fatigue loading at very low …

Investigation Of Scc Of High Strength Aluminum Alloys By Means Of Slow Strain Rate Test And Cyclic Anodic Polarization In Combination, Monica Trueba, Guido Russo, Stefano P. Trasatti, Sergio Lorenzi, Marina Cabrini, Antonietta Loconte

Stress-Assisted Corrosion Damage V

The stress corrosion cracking (SCC) behavior of high strength 7075-T6 and 2024-T3 Al alloys in NaCl solutions is investigated by means of slow strain rate test (SSRT) and cyclic anodic polarization in combination. Smooth, dog-bone shaped flat tension test specimens, having gage section areas of 40 mm² and 32 mm², respectively, and 90 mm of gage length, were machined in the longitudinal (rolling) direction from the commercial wrought sheets (Aviometal Spa). The tensile test was performed at a constant strain rate (ἐ = 10^-7, 10^-6 or 10^-5 s^-1) from a pre-load …

Assessment Of Seismic Retrofit Prioritization Methodology For Oregon's Highway Bridges Based On The Vulnerability Of Highway Segments, Selamawit Tesfayesus Mehary

Dissertations and Theses

Geologists have indicated that the question is not if a catastrophic earthquake will occur in Oregon but when one will occur. Scientists estimate that there is close to 40 percent conditional probability that a Cascadia subduction zone earthquake of magnitude 8.0 or above will strike Oregon in the next 50 years. In addition, the majority of Oregon's bridge inventory was built prior to the current understanding of bridge response and prior to current understanding of the expected earthquake demands. In order to minimize potential bridge damage in the case of an earthquake, one approach is to retrofit seismically deficient bridges. …

Adoption Of An Internet Of Things Framework For Distributed Energy Resource Coordination And Control, Tylor Slay

Dissertations and Theses

Increasing penetration of non-dispatchable renewable energy resources and greater peak power demand present growing challenges to Bulk Power System (BPS) reliability and resilience. This research investigates the use of an Internet of Things (IoT) framework for large scale Distributed Energy Resource (DER) aggregation and control to reduce energy imbalance caused by stochastic renewable generation. The aggregator developed for this research is Distributed Energy Resource Aggregation System (DERAS). DERAS comprises two AllJoyn applications written in C++. The first application is the Energy Management System (EMS), which aggregates, emulates, and controls connected DERs. The second application is the Distributed Management System (DMS), …

Advanced Recurrent Network-Based Hybrid Acoustic Models For Low Resource Speech Recognition, Jian Kang, Wei-Qiang Zhang, Wei-Wei Liu, Jia Liu, Michael T. Johnson

Electrical and Computer Engineering Faculty Publications

Recurrent neural networks (RNNs) have shown an ability to model temporal dependencies. However, the problem of exploding or vanishing gradients has limited their application. In recent years, long short-term memory RNNs (LSTM RNNs) have been proposed to solve this problem and have achieved excellent results. Bidirectional LSTM (BLSTM), which uses both preceding and following context, has shown particularly good performance. However, the computational requirements of BLSTM approaches are quite heavy, even when implemented efficiently with GPU-based high performance computers. In addition, because the output of LSTM units is bounded, there is often still a vanishing gradient issue over multiple layers. …

An Optimal Airline Revenue Management Seat Pricing Plan Model, Constantine M. Koursaris, James W. Marion Jr.

International Journal of Aviation, Aeronautics, and Aerospace

The goal of an airline is to sell tickets at the highest fare possible, thus yielding maximum profit for the stakeholders. As airline seat pricing is divided into different fare classes, a revenue management system is created and maintained to identify opportunity costs where the airline may sell an optimum number of available seats in both discounted fare and full fare classes. Ideally, under perfect conditions, the airline will sell all available seats at full capacity for each leg of a trip. Under non-ideal conditions for the airline, not all available seats may sell at either full fare or discounted …

A Comparative Study Of Signal Processing Methods For Fetal Phonocardiography Analysis, Venkata Akshay Bhargav Krishna Vadali

USF Tampa Graduate Theses and Dissertations

More than one million fetal deaths occur in the United States every year [1]. Monitoring the long-term heart rate variability provides a great amount of information about the fetal health condition which requires continuous monitoring of the fetal heart rate. All the existing technologies have either complex instrumentation or need a trained professional at all times or both. The existing technologies are proven to be impractical for continuous monitoring [2]. Hence, there is an increased interest towards noninvasive, continuous monitoring, and less expensive technologies like fetal phonocardiography.

Fetal Phonocardiography (FPCG) signal is obtained by placing an acoustic transducer on the …

Investigation Of The Acoustic Response Of A Confined Mesoscopic Water Film Utilizing A Combined Atomic Force Microscope And Shear Force Microscope Technique, Monte Allen Kozell

Dissertations and Theses

An atomic force microscopy beam-like cantilever is combined with an electrical tuning fork to form a shear force probe that is capable of generating an acoustic response from the mesoscopic water layer under ambient conditions while simultaneously monitoring force applied in the normal direction and the electrical response of the tuning fork shear force probe. Two shear force probes were designed and fabricated. A gallium ion beam was used to deposit carbon as a probe material. The carbon probe material was characterized using energy dispersive x-ray spectroscopy and scanning transmission electron microscopy. The probes were experimentally validated by demonstrating the …

Data-Driven Development Of A Roadside Safety Marketing Campaign For Tree Removal – Phase I, Cody S. Stolle, Thomas Ammon, Chris M. Vargas, Ronald K. Faller, Karla A. Lechtenberg, Erin L. Urbank

Nebraska Department of Transportation: Research Reports

Since the 1970s, tree crashes have been one of the most common and deadly fixed-object fatal crash types, resulting in more than 3,000 fatal crashes and 3,500 fatalities each year. While fatal tree crashes could be prevented by removing trees adjacent to the roadway, an extensive national tree removal project would be unnecessary, cost-prohibitive, and would experience significant political resistance.

The Midwest Pooled Fund Program jointly funded a research study to develop marketing methods and approaches which would focus on tree removal, replacement, or relocation in the most critical areas. Researchers conducted an extensive background investigation into tree crashes, other …

The Perceived Value Of Frequent Flyer Program Benefits Among Australian Travelers, Yi Gao, Madeline Carrigg, Robert Lewinski, Danielle Polderman, Paul Tkalcevic

International Journal of Aviation, Aeronautics, and Aerospace

Understanding the perceived value of frequent flyer program benefits is crucial for commercial operations of airlines. This study aimed to investigate if travelers value various benefits provided by airlines and if such valuation correlates with certain characteristics of travelers. Through a scenario-based questionnaire it was confirmed that travelers do value extra and premium benefits offered by airlines, and such valuation increases along with the distance of route. It was also been found that top-tier members were willing to make a much higher offer for the same benefits on long-haul international route than members of lower status, but such difference in …

Tunable Plasmonic Resonances In Highly Porous Nano-Bamboo Si-Au Superlattice-Type Thin Films, Ufuk Kılıç, Alyssa Mock, René Feder, Derek Sekora, Matthew J. Hilfiker, Rafal Korlacki, Eva Schubert, Christos Argyropoulos, Mathias Schubert

Department of Electrical and Computer Engineering: Faculty Publications

We report on fabrication of spatially-coherent columnar plasmonic nanostructure superlattice-type thin films with high porosity and strong optical anisotropy using glancing angle deposition. Subsequent and repeated depositions of silicon and gold lead to nanometer-dimension subcolumns with controlled lengths. The superlattice-type columns resemble bamboo structures where smaller column sections of gold form junctions sandwiched between larger silicon column sections (“nano-bamboo”). We perform generalized spectroscopic ellipsometry measurements and finite element method computations to elucidate the strongly anisotropic optical properties of the highly-porous nano-bamboo structures. The occurrence of a strongly localized plasmonic mode with displacement pattern reminiscent of a dark quadrupole mode is …

Relative Navigation: A Keyframe-Based Approach For Observable Gps-Degraded Navigation, David O. Wheeler, Daniel P. Koch, James S. Jackson, Timothy W. Mclain, Randal W. Beard

Faculty Publications

State estimation for micro air vehicles (MAVs) often depends heavily on reliable global measurements such as GPS. When global measurements are unavailable, additional sensors, such as cameras or laser scanners, are commonly used to provide measurements of the MAV’s translation and rotation relative to a previously observed keyframe image or scan. With the use of only relative sensors, however, the global position and heading of the vehicle are unobservable and cannot be reliably reconstructed. Many existing approaches work with respect to a global reference frame, resulting in a loss of state observability. This article highlights that unobservability leads to inconsistency …

Short Crack Tolerance Under Eac Conditions, Jtp Castro, Rv Landin, In Viçosa, Gr Altoé, Rrc Saúde

Stress-Assisted Corrosion Damage V

Notch sensitivity effects under environmentally-assisted cracking (EAC) conditions have been recently quantified considering the tolerance to short cracks that may start at their tips and become non-propagating after growing for a while, a behavior that depends on the stress gradients ahead of the notch tips and on the basic material resistances to crack initiation (S_EAC) and propagation (K_IEAC) inside an aggressive medium under static loadings. Such properties are time-independent, so they can be directly compared with the notch gradient-affected stress intensity factors of the short cracks that depart from notch tips. This model can provide a …

Emulating Balance Control Observed In Human Test Subjects With A Neural Network, Wade William Hilts

Dissertations and Theses

Human balance control is a complex feedback system that must be adaptable and robust in an infinitely varying external environment. It is probable that there are many concurrent control loops occurring in the central nervous system that achieve stability for a variety of postural perturbations. Though many engineering models of human balance control have been tested, no models of how these controllers might operate within the nervous system have yet been developed. We have focused on building a model of a proprioceptive feedback loop with simulated neurons. The proprioceptive referenced portion of human balance control has been successfully modeled by …

An Investigation Into Remote Sensing Techniques For Describing Hydraulic Roughness, Smriti Chaulagain

Civil Engineering ETDs

Riparian vegetation, an indicator of healthy river system, increases the hydraulic roughness and reduces the conveyance capacity of a channel. Vegetation provides dominant drag force influencing the velocity distribution, turbulence intensity and water depth. Thus, the study of hydraulic roughness due to vegetation is essential to determine the characteristics of flow. Traditionally, a constant Manning’s roughness value is assigned based on land cover maps and that does not adequately account for vegetation. The roughness due to vegetation are determined on the basis of its parameters like height, density, LAI and flexibility. Remote sensing data (LiDAR, aerial photos or satellite images) …

Inter-Comparison Of Thermal Measurements Using Ground-Based Sensors, Uav Thermal Cameras, And Eddy Covariance Radiometers, Alfonso F. Torres-Rua, Héctor Nieto, Christopher Parry, Manal Elarab, Wesley Collatz, Calvin Coopmans, Lynn Mckee, Mac Mckee, William P. Kustas

Civil and Environmental Engineering Faculty Publications

With the increasing availability of thermal proximity sensors, UAV-borne cameras, and eddy covariance radiometers there may be an assumption that information produced by these sensors is interchangeable or compatible. This assumption is often held for estimation of agricultural parameters such as canopy and soil temperature, energy balance components, and evapotranspiration. Nevertheless, environmental conditions, calibration, and ground settings may affect the relationship between measurements from each of these thermal sensors. This work presents a comparison between proximity infrared radiometer (IRT) sensors, microbolometer thermal cameras used in UAVs, and thermal radiometers used in eddy covariance towers in an agricultural setting. The information …

Evaluation Of Effectiveness Of Streambank Stabilization Practices And Flood Impact On Cedar River, Nebraska, Naisargi N. Dave

Department of Environmental Engineering: Theses and Other Student Research

Stream restoration has been a major environmental objective for preserving biodiversity, reducing loss of valuable cropland and improving water quality. The impact and efficiency of streambank stabilization practices has been simulated using erosion-prediction models; however, evaluation of the erosion-control practices to measure their efficiency is often neglected. This project monitored changes in fluvial geomorphology on the Cedar River in Nebraska and quantified the effectiveness of 18 sites with streambank stabilization practices. A flood event in 2010 due to dam failure acted as a major parameter in measuring the efficiency of the erosion control practices. The methodology included aerial imagery to …

In Situ Strain And Damage Monitoring Of Gfrp Laminates Incorporating Carbon Nanofibers Under Tension, Yanlei Wang, Yongshuai Wang, Baoguo Han, Baolin Wan, Gaochuang Cai, Ruijuan Chang

Civil and Environmental Engineering Faculty Research and Publications

In this study, conductive carbon nanofibers (CNFs) were dispersed into epoxy resin and then infused into glass fiber fabric to fabricate CNF/glass fiber-reinforced polymer (GFRP) laminates. The electrical resistance and strain of CNF/GFRP laminates were measured simultaneously during tensile loadings to investigate the in situ strain and damage monitoring capability of CNF/GFRP laminates. The damage evolution and conduction mechanisms of the laminates were also presented. The results indicated that the percolation threshold of CNFs content for CNF/GFRP laminates was 0.86 wt % based on a typical power law. The resistance response during monotonic tensile loading could be classified into three …

Conference Program, A.K. Vasudevan, Henry Holroyd, Ronald Latanision

Stress-Assisted Corrosion Damage V

No abstract provided.

Capacitive Pcb Security For Active Tamper And Alteration Detection, Casey Petersen

Electrical and Computer Engineering ETDs

The purpose of the research presented is to establish the viability of using capacitive based sensors for the purpose of hardware security at the Printed Circuit Board (PCB) level. Capacitive sensors are traditionally used to sense changes to the areas surrounding the sensing pads in applications such as sensing proximity, position, humidity, fluid levels and much more.

The specific sensor used for this research is an inductor-capacitor (LC) based Capacitance-to-Digital Converter. This configuration is virtually immune to EM noise because it is a tank circuit and therefore filters out the noise which, in the past, caused reliability issues with these …

An Ensemble Stacked Convolutional Neural Network Model For Environmental Event Sound Recognition, Shaobo Li, Yong Yao, Jie Hu, Guokai Liu, Xuemei Yao, Jianjun Hu

Faculty Publications

Convolutional neural networks (CNNs) with log-mel audio representation and CNN-based end-to-end learning have both been used for environmental event sound recognition (ESC). However, log-mel features can be complemented by features learned from the raw audio waveform with an effective fusion method. In this paper, we first propose a novel stacked CNN model with multiple convolutional layers of decreasing filter sizes to improve the performance of CNN models with either log-mel feature input or raw waveform input. These two models are then combined using the Dempster–Shafer (DS) evidence theory to build the ensemble DS-CNN model for ESC. Our experiments over three …

Characterizing Patterns In E. Coli Levels In Rio Grande River Water And Riverbed Sediments Near Albuquerque, Nm, James Fluke

Civil Engineering ETDs

In this work I examined how Fecal indicator Bacteria (FIB) behave in a large environmental system (Rio Grande near Albuquerque, ~60 km distance). I addressed the questions: How do FIB levels in river water and riverbed sediments of this reach change with distance along the river and throughout one year?

I conducted year-round river water and sediment sampling for concentration of E. coli bacteria, a persistent contaminant in the area. I found that over the year, E. coli loading in river water increased along the 60 km reach and E. coli in the sediments mainly increased near the Albuquerque urban …

Pore-Resolving Simulation Of Char Particle Gasification Using Micro-Ct, Greg Hingwah Fong, Scott Jorgensen, Simcha L. Singer

Mechanical Engineering Faculty Research and Publications

Understanding the interaction between transport, reaction and morphology at the scale of individual char particles is important for optimizing solid fuel gasification and combustion processes. However, most particle-scale models treat porous char particles as an effective porous continuum, even though the presence of large, irregular macropores, voids and fractures render such upscaled treatments mathematically invalid, and the models non-predictive. A new modeling framework is therefore proposed to elucidate the impact of morphology on char particle gasification and combustion. A pore-resolving, transient, three-dimensional simulation for gasification of a realistic coal char particle is developed based on X-ray micro-computed tomography (micro-CT). The …

Pulse Sharpening Circuit For Explosive Emission Cathode Driver, Nicholas D. Kallas

Electrical and Computer Engineering ETDs

Explosive field emission cathodes (EEC), used for the generation of relativistic electron beams, require short rise-time high-voltage pulses in order to minimize the extraction of off-energy electrons. To this end, a rise-time sharpening circuit has been developed at the Los Alamos National Laboratory (LANL). The circuit consists of a 7 nF water-filled peaking capacitor with an integrated self-breakdown switch designed to operate up to -300 kV. This unit is intended to reduce the rise-time of a 4-stage Type-E PFN Marx Generator that will be used to study operational characteristics of velvet cathodes. Simulations of the peaking circuit show a reduction …