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Brigham Young University

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Articles 3931 - 3960 of 4850

Full-Text Articles in Engineering

Time-Varying Mimo Channels: Parametric Statistical Modeling And Experimental Results, Michael A. Jensen, Shuangquan Wang, Ali Abdi, Jari Salo, Hassan M. El-Sallabi, Jon W. Wallace, Pertti Vainikainen Jul 2007

Time-Varying Mimo Channels: Parametric Statistical Modeling And Experimental Results, Michael A. Jensen, Shuangquan Wang, Ali Abdi, Jari Salo, Hassan M. El-Sallabi, Jon W. Wallace, Pertti Vainikainen

Faculty Publications

Accurate characterization of multiple-input multiple-output (MIMO) fading channels is an important prerequisite for the design of multiantenna wireless-communication systems. In this paper, a single-bounce two-ring statistical model for the time-varying MIMO flat fading channels is proposed. In the model, both the base and mobile stations are surrounded by their own ring of scatterers. For the proposed model, a closed-form expression for the spatio-temporal cross-correlational function between any two subchannels is derived, assuming single-bounce scattering. The new analytical expression includes several key physical parameters of interest such as the mean angle-of-departure, the mean angle-of-arrival, the associated angle spreads, and the Doppler …

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A New Method For Treating Wells In Reservoir Simulation, Gregory M. Gessel Jun 2007

A New Method For Treating Wells In Reservoir Simulation, Gregory M. Gessel

Theses and Dissertations

A new method for formulating finite difference equations for reservoir simulation has been developed. It can be applied throughout the entire simulated reservoir or to local segments. When applied to cells containing vertical, fully penetrating, straight-line wells in a homogeneous reservoir, the resulting equations are equivalent to Peaceman's classical well equations used in most reservoir simulators today. However, when the new finite difference equations are applied to both the well-containing cells, and their neighbors, the accuracy of the simulation improves substantially. The method produces still better accuracy results when applied throughout the reservoir. Unlike the Peaceman correction, the new method …

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Vector Field Path Following For Miniature Air Vehicles, Timothy Mclain, Derek R. Nelson, D. Blake Barber, Randall W. Beard Jun 2007

Vector Field Path Following For Miniature Air Vehicles, Timothy Mclain, Derek R. Nelson, D. Blake Barber, Randall W. Beard

Faculty Publications

In this paper, a method for accurate path following for miniature air vehicles is developed. The method is based on the notion of vector fields, which are used to generate desired course inputs to inner-loop attitude control laws. Vector-field path-following control laws are developed for straight-line paths and circular arcs and orbits. Lyapunov stability arguments are used to demonstrate asymptotic decay of path-following errors in the presence of constant wind disturbances. Experimental flight tests have demonstrated mean path-following errors on less than one wingspan for straight-line and orbit paths and less than three wingspans for paths with frequent changes in …

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Three Enabling Technologies For Vision-Based, Forest-Fire Perimeter Surveillance Using Multiple Unmanned Aerial Systems, Ryan S. Holt Jun 2007

Three Enabling Technologies For Vision-Based, Forest-Fire Perimeter Surveillance Using Multiple Unmanned Aerial Systems, Ryan S. Holt

Theses and Dissertations

The ability to gather and process information regarding the condition of forest fires is essential to cost-effective, safe, and efficient fire fighting. Advances in sensory and autopilot technology have made miniature unmanned aerial systems (UASs) an important tool in the acquisition of information. This thesis addresses some of the challenges faced when employing UASs for forest-fire perimeter surveillance; namely, perimeter tracking, cooperative perimeter surveillance, and path planning. Solutions to the first two issues are presented and a method for understanding path planning within the context of a forest-fire environment is demonstrated. Both simulation and hardware results are provided for each …

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Performance Of Mimo Space-Time Coding Algorithms On A Parallel Dsp Test Platform, Beau C. Neal Jun 2007

Performance Of Mimo Space-Time Coding Algorithms On A Parallel Dsp Test Platform, Beau C. Neal

Theses and Dissertations

Commercial Off The Shelf (COTS) hardware has the advantages of low cost, modularity, and is easily upgraded. For Multiple-Input Multiple-Output (MIMO) space-time algorithms to be practical they must have the processing capability to execute in real-time. This makes COTS ideal for real-time MIMO research where the processing power increases exponentially with a linear increase in antennas. The BYU Electrical Engineering wireless lab has designed and built an eight processor transmitter and a twenty processor receiver to research and develop MIMO wireless communication. The Alamouti, 2 x 2 and 4 x 4 differential space-time MIMO algorithms have been partially implemented on …

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Optimization Of Nano-Magneto-Optic Sensitivity Using Dual Dielectric Layer Enhancement, Aaron R. Hawkins, J. D. Maas, S. Wang, A. Barman, Holger Schmidt, S. Kwon, B. Harteneck, S. Cabrini, J. Bokor Jun 2007

Optimization Of Nano-Magneto-Optic Sensitivity Using Dual Dielectric Layer Enhancement, Aaron R. Hawkins, J. D. Maas, S. Wang, A. Barman, Holger Schmidt, S. Kwon, B. Harteneck, S. Cabrini, J. Bokor

Faculty Publications

We discuss maximization of the sensitivity of magneto-optical detection of single nanomagnets. We show that a combination of optimized dielectric coating on the magnets with an antireflection coated substrate can increase the areal magneto-optic sensitivity by about three orders of magnitude in the deep nanometer range. A dual layer nanofabrication process is developed to implement this approach, and magnetization switching of single nickel nanomagnets with 50 nm diameter is demonstrated.

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An Investigation Of A Positive Engagement, Continuously Variable Transmission, Brian S. Andersen Jun 2007

An Investigation Of A Positive Engagement, Continuously Variable Transmission, Brian S. Andersen

Theses and Dissertations

A continuously variable transmission (CVT) is a type of transmission that allows an infinitely variable ratio change within a finite range, allowing the engine to continuously operate in an efficient or high performance range. A brief history of CVTs is presented, including the families under which they can be categorized. A new family of CVTs, with the classification of positive engagement, is presented. Three different published embodiments of CVTs of the positive engagement type are presented describing a meshing problem that exists apparently regardless of the embodiment in this family. The problem is called the non-integer tooth problem and its …

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Computationally Efficient Modeling Of Transient Radiation In A Purely Scattering Foam Layer, Rudolph Scott Larson Jun 2007

Computationally Efficient Modeling Of Transient Radiation In A Purely Scattering Foam Layer, Rudolph Scott Larson

Theses and Dissertations

An efficient solution method for evaluating radiative transport in a foam layer is a valuable tool for predicting the properties of the layer. Two different solution methods have been investigated. First, a reverse Monte Carlo (RMC) simulation has been developed. In the RMC simulation photon bundles are traced backwards from a detector to the source where they were emitted. The RMC method takes advantage of time reflection symmetry, allowing the photons to be traced backwards in the same manner they are tracked in a standard forward Monte Carlo scheme. Second, a reduced order model based on the singular value decomposition …

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Optimal Noise Matching For Mutually-Coupled Arrays, Michael A. Jensen, Karl F. Warnick Jun 2007

Optimal Noise Matching For Mutually-Coupled Arrays, Michael A. Jensen, Karl F. Warnick

Faculty Publications

From classical two-port noise theory, the noise figure of an amplifier is minimized when a source is matched to a particular optimal reflection coefficient at the amplifier input. In this paper, we show that this result extends in a natural way to the multiport case, with a coupled N-port source network such as an array antenna connected by a multiport matching network to the inputs of N low-noise amplifiers. For optimal noise performance, the matching network must decouple the array and present isolated, individually noise-matched ports to the amplifier inputs.

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Band Discontinuity Measurements Of The Wafer Bonded Ingaas/Si Heterojunction, Aaron R. Hawkins, Kyle S. Mckay, Felix P. Lu, Jungsang Kim, Changhyun Yi, April S. Brown May 2007

Band Discontinuity Measurements Of The Wafer Bonded Ingaas/Si Heterojunction, Aaron R. Hawkins, Kyle S. Mckay, Felix P. Lu, Jungsang Kim, Changhyun Yi, April S. Brown

Faculty Publications

p-type InGaAs/Si heterojunctions were fabricated through a wafer fusion bonding process. The relative band alignment between the two materials at the heterointerface was determined using current-voltage (I-V) measurements and applying thermionic emission-diffusion theory. The valence and conduction band discontinuities for the InGaAs/Si interface were determined to be 0.48 and 0.1 eV, respectively, indicating a type-II band alignment.

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Mechanisms Causing Ferric Staining In The Secondary Water System Of Brigham City, Utah, Robert Derring Wallace May 2007

Mechanisms Causing Ferric Staining In The Secondary Water System Of Brigham City, Utah, Robert Derring Wallace

Theses and Dissertations

Water from Mantua reservoir has, during some years, exhibited reddish-brown staining when used by Brigham City for irrigation. I propose that seasonal fluctuations in the reservoir chemistry create an environment conducive to dissolving iron from the iron-rich sediments, which subsequently precipitate during irrigation, resulting in a staining event. These conditions are produced by chemical and biological decomposition of organic matter, coupled with isolation of the hypolimnetic waters, which results in seasonal low concentrations of dissolved oxygen in these waters. Under these specific circumstances, anaerobic conditions develop creating a geochemical environment that causes iron and manganese reduction from Fe(III) to Fe(II) …

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Dynamic Full-Scale Testing Of A Pile Cap With Loose Silty Sand Backfill, Immanuel Kaleoonalani Runnels May 2007

Dynamic Full-Scale Testing Of A Pile Cap With Loose Silty Sand Backfill, Immanuel Kaleoonalani Runnels

Theses and Dissertations

Pile caps are used in foundation design to aid multiple single piles to act as a pile group to resist lateral forces that may cause overturning moments. The pile cap and pile group resist these forces by pile-soil-pile interaction, base and side friction along the pile cap-backfill interface, and passive earth resistance. Passive earth resistance has been neglected in design due to a limited amount of full-scale testing. This research presents the results of a combination of hydraulic actuator and eccentric-mass shaker full-scale testing of a pile cap with loose silty sand backfill to quantify the contribution of the passive …

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On-Chip Surface-Enhanced Raman Scattering Detection Using Integrated Liquid-Core Waveguides, Aaron R. Hawkins, Evan J. Lunt, Phillip Measor, Leo Seballos, Dongliang Yin, Jin Z. Zhang, Holger Schmidt May 2007

On-Chip Surface-Enhanced Raman Scattering Detection Using Integrated Liquid-Core Waveguides, Aaron R. Hawkins, Evan J. Lunt, Phillip Measor, Leo Seballos, Dongliang Yin, Jin Z. Zhang, Holger Schmidt

Faculty Publications

The authors demonstrate surface-enhanced Raman scattering (SERS) detection on an optofluidic chip. Interconnected solid- and liquid-core antiresonant reflecting optical waveguides (ARROWs) form a planar beam geometry that allows for high mode intensities along microfluidic channels containing molecules optimized for SERS. The excitation power and concentration dependence of SERS from rhodamine 6G (R6G) molecules adsorbed to silver nanoparticles were systematically studied. The data can be described by a model that takes into account the microphotonic structure. Detection sensitivity to a minimum concentration of 30 nM is found, demonstrating the suitability of ARROW-based optofluidic chips for high sensitivity detection with molecular specificity

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Large-Displacement Linear-Motion Compliant Mechanisms, Allen B. Mackay May 2007

Large-Displacement Linear-Motion Compliant Mechanisms, Allen B. Mackay

Theses and Dissertations

Linear-motion compliant mechanisms have generally been developed for small displacement applications. The objective of the thesis is to provide a basis for improved large-displacement linear-motion compliant mechanisms (LLCMs). One of the challenges in developing large-displacement compliant mechanisms is the apparent performance tradeoff between displacement and off-axis stiffness. In order to facilitate the evaluation, comparison, and optimization of the performance of LLCMs, this work formulates and presents a set of metrics that evaluates displacement and off-axis stiffness. The metrics are non-dimensionalized and consist of the relevant characteristics that describe mechanism displacement, off-axis stiffness, actuation force, and size. Displacement is normalized by …

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Evaluation Of Laboratory Durability Tests For Stabilized Aggregate Base Materials, Matthew B. Roper May 2007

Evaluation Of Laboratory Durability Tests For Stabilized Aggregate Base Materials, Matthew B. Roper

Theses and Dissertations

The Portland Cement Association commissioned a research project at Brigham Young University to compare selected laboratory durability tests available for assessing stabilized aggregate base materials. The laboratory research associated with this project involved two granular base materials, three stabilizers at three concentration levels each, and three durability tests in a full-factorial experimental design. The granular base materials consisted of an aggregate-reclaimed asphalt pavement blend obtained from Interstate 84 (I-84) and a crushed limestone obtained from U.S. Highway 91 (US-91), while the three stabilizer types included Class C fly ash, lime-fly ash, and Type I/II Portland cement. Specimens were tested for …

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Size Dependent Damping In Picosecond Dynamics Of Single Nanomagnets, Aaron R. Hawkins, J. D. Maas, S. Wang, A. Barman, Holger Schmidt, Liddle A. Kwon, J. Bokor May 2007

Size Dependent Damping In Picosecond Dynamics Of Single Nanomagnets, Aaron R. Hawkins, J. D. Maas, S. Wang, A. Barman, Holger Schmidt, Liddle A. Kwon, J. Bokor

Faculty Publications

The authors use time-resolved cavity-enhanced magneto-optical Kerr spectroscopy to study the damping of magnetization precession in individual cylindrical nickel nanomagnets. A wide range of shapes (diameters of 5 µm–125 nm and aspect ratio: 0.03–1.2) is investigated. They observe a pronounced difference in damping between the micro- and nanomagnets. Microscale magnets show large damping at low bias fields, whereas nanomagnets exhibit bias field-independent damping. This behavior is explained by the interaction of in-plane and out-of-plane precession modes in microscale magnets that results in additional dissipative channels. The small and robust damping values on the nanoscale are promising for implementation of controlled …

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Pharmacokinetics Of Ultrasonically-Released, Micelle-Encapsulated Doxorubicin In The Rat Model And Its Effect On Tumor Growth, Bryant J. Staples May 2007

Pharmacokinetics Of Ultrasonically-Released, Micelle-Encapsulated Doxorubicin In The Rat Model And Its Effect On Tumor Growth, Bryant J. Staples

Theses and Dissertations

Chemotherapy is one of the most successful cancer treatments used today. Unfortunately, the amount of chemotherapy a patient can receive is limited by the associated negative side effects, such as cardiotoxicity, immune system suppression, and nephrotoxicity. Encapsulation of these drugs, Doxorubicin (DOX) in particular, in stabilized Pluronic micelles (Plurogel TM) shows success in limiting these harmful side effects. In previous studies, low-frequency ultrasound (US) has been shown, in vitro, to locally release DOX from these micelles. In this study, a novel drug delivery system involving the encapsulation of DOX in Plurogel and the release of the drug at the tumor …

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Investigation Of The Iron Oxidation Kinetics In Mantua Reservoir, Scott H. Lathen May 2007

Investigation Of The Iron Oxidation Kinetics In Mantua Reservoir, Scott H. Lathen

Theses and Dissertations

Irrigation of the municipal cemetery in Brigham City, Utah resulted in stained headstones in 2001 and 2002. The water used in the irrigation came from Mantua reservoir, a medium sized impoundment situated near the mouth of Box Elder Canyon. In order for Brigham City to establish a city wide secondary pressurized irrigation system using water from Mantua reservoir, the cause and the source of staining problem must be determined. Previous research (Wallace 2006) determined that the source of the staining was the reduction of iron found in Mantua Reservoir sediments that occurred when seasonal variations in the reservoir caused anaerobic …

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A Prioritization Process For Access Management Implementation In Utah, Kordel T. Braley May 2007

A Prioritization Process For Access Management Implementation In Utah, Kordel T. Braley

Theses and Dissertations

Appropriate access management techniques can improve the safety and efficiency of arterial roads. In order to determine which roads can most benefit by the implementation of access management techniques, a prioritization process was developed to recommend various access management treatments such as limiting access points, installing raised medians, and ensuring adequate signal spacing along corridors. To serve as the basis for the performance index, a database was created including identifying features, characteristics, and crash history for 175 arterial road segments on Utah state routes. Stepwise linear regression was applied to the data collected to determine which characteristics of the roads …

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Evaluation And Installation Guidelines For Advance Warning Signal Systems In Utah, Aaron Paul Jensen May 2007

Evaluation And Installation Guidelines For Advance Warning Signal Systems In Utah, Aaron Paul Jensen

Theses and Dissertations

Advance warning signals (AWS) provide information warning drivers in advance of the end-of-green phase for an approaching signalized intersection. The purpose of this research was to develop guidelines for the placement of AWS in Utah, both conditions to evaluate the need for AWS installation and guidelines for the AWS system design. The conditions were based on literature of other transportation agencies that had similar AWS systems and were developed using the Policy Delphi method. The Policy Delphi method is the development of a specific policy area through the means of discussion by a committee of experts correlating views and information …

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Multi-Stable Compliant Rolling-Contact Elements, Peter Andrew Halverson May 2007

Multi-Stable Compliant Rolling-Contact Elements, Peter Andrew Halverson

Theses and Dissertations

The purpose of this research is the development of design concepts and models of large-angle, compliant, multistable, revolute joints. This research presents evidence of the capability of these models and concepts by presenting a case study in which the miniaturization of revolute joints are examined. Previous attempts at multistable revolute joints can be categorized into two categories: compliant and non-compliant mechanisms. Non-compliant multistable revolute joints are typified by a combination of pin-in-slot joints, springs, and detents. Due to factors inherit in design, noncompliant joints often succumb to friction, wear, and undesirable motion, that leads to a decline in performance. Compliant …

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Use Of The Clegg Impact Soil Tester To Access Rutting Susceptiblity Of Cement-Treated Base Material Under Early Trafficking, Garth B. Reese May 2007

Use Of The Clegg Impact Soil Tester To Access Rutting Susceptiblity Of Cement-Treated Base Material Under Early Trafficking, Garth B. Reese

Theses and Dissertations

In order to avoid the occurrence of early-age damage, cement-treated base (CTB) materials must be allowed to cure for a period of time before the pavement can be opened to traffic. Trafficking of a CTB before sufficient strength gain has occurred can lead to marring or rutting of the treated layer. The specific objectives of this research were to examine the correlation between Clegg impact values (CIVs) determined using a heavy Clegg impact soil tester and rut depths measured in newly constructed CTB and subsequently establish a threshold CIV at which rutting should not occur.The experimental work included field testing …

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Autonomous Landing Of Miniature Aerial Vehicles, D. Blake Barber, Stephen R. Griffiths, Timothy W. Mclain, Randal W. Beard May 2007

Autonomous Landing Of Miniature Aerial Vehicles, D. Blake Barber, Stephen R. Griffiths, Timothy W. Mclain, Randal W. Beard

Faculty Publications

This paper outlines an approach for automated landing of miniature aerial vehicles (MAVs). A landing algorithm defining the landing flight path as a function of height above ground, and the control strategies for following the path, are described. Two methods are presented for estimating height above ground, one based on barometric pressure measurements and the other utilizing optic-flow measurements. The development of an optic-flow sensor and associated sampling strategies are described. Utilizing estimates of height above ground from barometric pressure and optic-flow measurements, repeated landings were performed with a 1.5 m wingspan MAV. With height above ground estimated from barometric …

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An Overview Of Mav Research At Brigham Young University, Timothy W. Mclain, Randal W. Beard, D. Blake Barber, Nathan B. Knoebel May 2007

An Overview Of Mav Research At Brigham Young University, Timothy W. Mclain, Randal W. Beard, D. Blake Barber, Nathan B. Knoebel

Faculty Publications

This paper summarizes research efforts at Brigham Young University related to the control of miniature aerial vehicles (MAVs). Recent results in the areas of vector field path following, precision landing and target prosecution, target localization, obstacle detection and avoidance, tailsitter aircraft control, and cooperative control are presented.

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Spatial And Temporal Behavior Of Microwave Backscatter Directional Modulation Over The Saharan Ergs, David G. Long, Haroon Stephen May 2007

Spatial And Temporal Behavior Of Microwave Backscatter Directional Modulation Over The Saharan Ergs, David G. Long, Haroon Stephen

Faculty Publications

Radar backscatter (σ˚) from ergs is modulated with view direction [incidence (θ) and azimuth (φ) angles], where the modulation characteristics reflect the surface geometry. σ˚ also varies spatially and reflects the spatial inhomogeneity of the sand surface. We use σ˚ measurements at different θ and φ angles from the NASA, European Remote Sensing satellite, and SeaWinds scatterometers to understand the relationship between wind and erg bedforms. A model incorporating the σ˚ φ-modulation and spatial inhomogeneity is proposed. Surface slope variations are related to the σ˚ spatial inhomogeneity. We compare the backscatter model results with numerically predicted wind direction data provided …

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Experimental Characterization Of The Outdoor Mimo Wireless Channel Temporal Variation, Michael A. Jensen, Karl F. Warnick, Jon W. Wallace, Ajay Gummalla, Harry B. Lee May 2007

Experimental Characterization Of The Outdoor Mimo Wireless Channel Temporal Variation, Michael A. Jensen, Karl F. Warnick, Jon W. Wallace, Ajay Gummalla, Harry B. Lee

Faculty Publications

Time-variant multiple-input multiple-output (MIMO) channels are measured in an outdoor campus environment at 2.45 GHz with directional patch arrays and omnidirectional monopole arrays. A number of useful metrics are proposed for quantifying time variation in MIMO channels: eigenvalue level crossing rate, eigenvector angular deviation, and capacity loss for delayed transmit and receive channel state information (CSI). Measurements in four different environments confirm the strong correlation between angular spread of multipath and MIMO channel time variability. The rate of time variation is also strongly influenced by the type of array, indicating that directional elements may be advantageous for highly mobile environments. …

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The Relationship Between Antenna Loss And Superdirectivity In Mimo Systems, Michael A. Jensen, Nicolas W. Bikhazi May 2007

The Relationship Between Antenna Loss And Superdirectivity In Mimo Systems, Michael A. Jensen, Nicolas W. Bikhazi

Faculty Publications

Multiple-input multiple-output (MIMO) communication systems can theoretically use array superdirectivity to optimally exploit the propagation channel. This superdirectivity leads to very large capacity bounds, particularly when the antennas are closely spaced. However, because superdirective behavior is difficult to achieve in practice, new capacity bounds have been formulated for the case where the level of array superdirectivity is constrained. Existing capacity analyses limit the superdirectivity in a suboptimal way. In this paper, the impact of superdirectivity in the capacity solution is limited by introducing finite ohmic loss in the transmit and receive antenna elements. Computational results reveal that even a small …

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Vision-Based Landing Of Fixed-Wing Miniature Air Vehicles, Blake Barber, Timothy Mclain, Barrett Edwards May 2007

Vision-Based Landing Of Fixed-Wing Miniature Air Vehicles, Blake Barber, Timothy Mclain, Barrett Edwards

Faculty Publications

This paper outlines a method for using vision-based feedback to accurately land a MAV on a visually identifiable target of approximately known location. The method presented is robust to wind, capable of handling both stationary and moving targets, and capable of cor- recting for camera misalignment, state estimation biases, and parameter estimation biases. Landing results from actual flight tests are presented which demonstrate the effectiveness of the proposed method.

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Probabilistic Searching Using A Small Unmanned Aerial Vehicle, Steven R. Hansen, Timothy W. Mclain, Michael A. Goodrich May 2007

Probabilistic Searching Using A Small Unmanned Aerial Vehicle, Steven R. Hansen, Timothy W. Mclain, Michael A. Goodrich

Faculty Publications

Ground breaking concepts in optimal search theory were developed during World War II by the U.S. Navy. These concepts use an assumed detection model to calculate a detection probability rate and an optimal search allocation. Although this theory is useful in determining when and where search effort should be applied, it offers little guidance for the planning of search paths. This paper explains how search theory can be applied to path planning for an SUAV with a fixed CCD camera. Three search strategies are developed: greedy search, contour search, and composite search. In addition, the concepts of search efficiency and …

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Final Report: Shf Channel Modeling Over Sea-Based Test Ranges, Qiang Lei, Michael D. Rice Apr 2007

Final Report: Shf Channel Modeling Over Sea-Based Test Ranges, Qiang Lei, Michael D. Rice

Faculty Publications

This work was supported by the Science & Technology Test & Evaluation Spectrum Efficient Technologies Program sponsored by the US Air Force under contract F04611-02-C-0020. Channel sounding data collected from an airborne transmitter over the Pacific Ocean off the coast of Pt. Mugu, Naval Air Station, was analyzed and used to model multipath propagation over the ocean. The experiments showed that at 8.000 GHz, over the water multipath propagation is well modeled by a three-ray propagation model. The first ray (or propagation path) is the line-of-sight propagation path. The second ray is a strong specular reflection determined by the geometry …

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