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Articles 1 - 30 of 47
Full-Text Articles in Engineering
Simulation And Density Functional Study Of A Simple Membrane Separating Two Restricted Primitive Model Electrolytes, Richard L. Rowley, Dezso Boda, Douglas Henderson, Stefan Sokolowski
Simulation And Density Functional Study Of A Simple Membrane Separating Two Restricted Primitive Model Electrolytes, Richard L. Rowley, Dezso Boda, Douglas Henderson, Stefan Sokolowski
Faculty Publications
A simple membrane, supporting charge densities on its inner and outer surfaces, is considered. In addition to the electrostatic potential, the membrane interacts with the surrounding fluid by a short range van der Waals-like potential. The fluid beyond the outer surface is a three-component restricted primitive electrolyte consisting of two cations and one anion. The membrane is impermeable to one of the cations so that the fluid in the membrane and beyond the inner surface is a two-component restricted primitive electrolyte. We use Monte Carlo simulations and density functional theory to study the density profiles of the electrolyte and the …
Accuracy Of Scatterometer-Derived Winds Using The Cramer-Rao Bound, David G. Long, Travis E. Oliphant
Accuracy Of Scatterometer-Derived Winds Using The Cramer-Rao Bound, David G. Long, Travis E. Oliphant
Faculty Publications
A wind scatterometer makes measurements of the normalized radar-backscatter coefficient O of the ocean surface. To retrieve the wind, a geophysical model function (GMF), which relates O to the near-surface wind, is used. The wind vector can be estimated using maximum-likelihood techniques from several O measurements made at different azimuth angles. The probability density of the measured O is assumed to be Gaussian with a variance that depends on the true O and therefore, depends on the wind through the GMF. With this model for wind estimation, the Cramer-Rao (C-R) bound is derived for wind estimation, and its implications for …
Low-Frequency Noise In N-Gan With High Electron Mobility, M. E. Levinshtein, S. L. Rumyantsev, D. C. Look, R. J. Molnar, M. Asif Khan, Grigory Simin, V. Adivarahan, M. S. Shur
Low-Frequency Noise In N-Gan With High Electron Mobility, M. E. Levinshtein, S. L. Rumyantsev, D. C. Look, R. J. Molnar, M. Asif Khan, Grigory Simin, V. Adivarahan, M. S. Shur
Faculty Publications
We report on the results of measurements of low frequency noise in n-type gallium nitride (GaN) grown on sapphire with 300 K electron mobility of 790 cm2/V s. The noise spectra have the form of 1/f noise with a Hooge parameter α of approximately 5×10−2. This value of α is two orders of magnitude smaller than that observed before in n-GaN. The obtained results show that the level of flicker noise in GaN, just like that in GaAs and Si, strongly depends on the structural perfection of the material (the amplitude of the 1/f …
Piezoelectric Doping In Alingan/Gan Heterostructures, M. Asif Khan, J. W. Yang, Grigory Simin, R. Gaska, M. S. Shur, A. D. Bykovski
Piezoelectric Doping In Alingan/Gan Heterostructures, M. Asif Khan, J. W. Yang, Grigory Simin, R. Gaska, M. S. Shur, A. D. Bykovski
Faculty Publications
We report on the piezoelectricdoping and two-dimensional (2D) electron mobility in AlInGaN/GaN heterostructures grown on 6H–SiC substrates. The contribution of piezoelectricdoping to the sheet electron density was determined using an In-controlled built-in strain-modulation technique. Our results demonstrate that in strained AlGaN/GaN heterostructures, the piezoelectric field generates at least 50% of the 2D electrons. The strain modulation changes the potential distribution at the heterointerface, which, in turn, strongly affects the 2D electron mobility, especially at cryogenic temperatures. The obtained results demonstrate the potential of strain engineering and piezoelectricdoping for GaN-based electronics.
Nonlinear Robust Missile Autopilot Design Using Successive Galerkin Approximation, Timothy Mclain, Randal W. Beard
Nonlinear Robust Missile Autopilot Design Using Successive Galerkin Approximation, Timothy Mclain, Randal W. Beard
Faculty Publications
The application of a new nonlinear robust control strategy to the design of missile autopilots is presented. The control approach described and demonstrated here is based upon the numerical solution of the Hamilton-Jacobi-Isaacs equation by Successive Galerkin Approximation. Using this approach, feedback controllers are computed by an iterative application of a numerical Galerkin-type PDE solver. Application of this approach to the design of a pitch-axis autopilot for a missile having uncertain pitch moment and lift force is described.
Successive Galerkin Approximation Of The Isaacs Equation, Timothy Mclain, Randal W. Beard, John T. Wen
Successive Galerkin Approximation Of The Isaacs Equation, Timothy Mclain, Randal W. Beard, John T. Wen
Faculty Publications
The successive Galerkin approximation (SGA) algorithm has recently been developed for approximating solutions to the Hamilton-Jacobi-Isaacs equation. The algorithm produces feedback control laws that are stabilizing on a well-defined region of state space. The objective of this paper is to demonstrate the application of the SGA algorithm to two simple examples. The examples serve several purposes: first they illustrate how the algorithm is applied in a setting that is simple enough to write out in detail, second they demonstrate the convergence of the algorithm in a setting where the actual solution can be derived analytically.
Successive Galerkin Approximation Of A Nonlinear Optimal Attitude Control, Timothy Mclain, Randal W. Beard, Johnathan Lawton
Successive Galerkin Approximation Of A Nonlinear Optimal Attitude Control, Timothy Mclain, Randal W. Beard, Johnathan Lawton
Faculty Publications
This paper presents the application of the successive Galerkin approximation (SGA) to the Hamilton-Jacobi-Bellman equation to obtain solutions of the optimal attitude control problem. Galerkin's method approximates the value function by a truncated Galerkin series expansion. To do so, a truncated Galerkin basis set is formed. A sufficient number of functions must be included in this Galerkin basis set in order to guarantee that the solution will be a stabilizing control. By increasing the size of the Galerkin basis the quality of the approximation is improved at the cost of rapid growth in the computation load of the SGA. A …
A Five-Year Development Plan For The California Aviation Database, H.-S. Jacob Tsao
A Five-Year Development Plan For The California Aviation Database, H.-S. Jacob Tsao
Faculty Publications
The California Aviation Database (CAvD) project was suggested by Caltrans Aeronautics Program to fulfill a need of the planners involved in aviation system planning and programming activities to locate and access aviation data and information in an efficient and comprehensive way. CAvD is being implemented in the form of an Internet website and is currently intended as a five-year project. However, the development can be accelerated, and the duration will depend on the available resources. CAvD is a joint project between the National Center of Excellence for Aviation Operations Research (NEXTOR) and the California Department of Transportation (Caltrans). Its primary …
Synthesis And Experimental Testing Of A Nonlinear Optimal Tracking Controller, Timothy Mclain, Randal W. Beard, Christopher A. Bailey
Synthesis And Experimental Testing Of A Nonlinear Optimal Tracking Controller, Timothy Mclain, Randal W. Beard, Christopher A. Bailey
Faculty Publications
This paper presents a novel approach for developing tracking controllers for nonlinear systems. The approach involves the numerical solution, by Galerkin approximation, of the time-varying Hamilton-Jacobi-Bellman (HJB) equation and results in a nonlinear controller approximating the optimal tracking control law for a specified desired trajectory and cost function. Experimental results are presented for a nonlinear pendulum system.
Oxygen Permeation Through Composite Oxide-Ion And Electronic Conductors, Kevin Huang, Michael Schroeder, John B. Goodenough
Oxygen Permeation Through Composite Oxide-Ion And Electronic Conductors, Kevin Huang, Michael Schroeder, John B. Goodenough
Faculty Publications
Oxygen permeation through composites consisting of four well-known oxide-ion conductors and a noble metal, Pd or Ag, is reported. The oxides were Zr0.9Y0.1O1.95 (YSZ), (Bi1.75Y0.25O3)0.95(CeO2)0.05 (BYC5), Ce0.8Sm0.2O1.9 (SSC), and La0.8Sr0.2Ga0.83Mg0.17O2.815 (LSGM). The results show that (BYC5 + Ag) yields the highest oxygen permeation flux, but the composite deteriorates with time. The composites (SSC + Pd), (LSGM + Pd), and (YSZ + Pd) give stable, but relatively lower oxygen permeation flux …
Stratified Volume Diffractive Optical Elements As High Efficiency Gratings, Gregory P. Nordin, D. M. Chambers
Stratified Volume Diffractive Optical Elements As High Efficiency Gratings, Gregory P. Nordin, D. M. Chambers
Faculty Publications
We propose stratified volume diffractive optical elements as a new type of diffractive optical element that is capable of functioning as a high-efficiency grating in applications with requirements not suited to traditional holographic or diffractive optical techniques. In this approach, diffractive optical fabrication methods are used to construct an optical structure that emulates volume grating behavior. We discuss the diffraction properties of stratified volume diffractive optical elements and compare them with those used previously in both volume holographic optical elements and stratified volume holographic optical elements. A systematic design process is then presented for deriving structure parameters. We illustrate this …
Ultrasonic Enhancement Of Antibiotic Action On Escherichia Coli Biofilms: An In Vivo Model, Andrea M. Rediske, Beverly L. Roeder, Maren K. Brown, Jared L. Nelson, Rachel L. Robison, David O. Draper, G. Bruce Schaalje, Richard A. Robison, William G. Pitt
Ultrasonic Enhancement Of Antibiotic Action On Escherichia Coli Biofilms: An In Vivo Model, Andrea M. Rediske, Beverly L. Roeder, Maren K. Brown, Jared L. Nelson, Rachel L. Robison, David O. Draper, G. Bruce Schaalje, Richard A. Robison, William G. Pitt
Faculty Publications
Biofilm infections are a common complication of prosthetic devices in humans. Previous in vitro research has determined that low-frequency ultrasound combined with aminoglycoside antibiotics is an effective method of killing biofilms. We report the development of an in vivo model to determine if ultrasound enhances antibiotic action. Two 24-h-old Escherichia coli (ATCC 10798) biofilms grown on polyethylene disks were implanted subcutaneously on the backs of New Zealand White female rabbits, one on each side of the spine. Low-frequency (28.48-kHz) and low-power-density (100- and 300-mW/cm2) continuous ultrasound treatment was applied for 24 h with and without systemic administration of gentamicin. The …
Postlaunch Sensor Verification And Calibration Of The Nasa Scatterometer, David G. Long, Wu-Yang Tsai, James E. Graf, Carroll Winn, James N. Huddleston, R. Scott Dunbar, Michael H. Freilich, Frank J. Wentz, W. Linwood Jones
Postlaunch Sensor Verification And Calibration Of The Nasa Scatterometer, David G. Long, Wu-Yang Tsai, James E. Graf, Carroll Winn, James N. Huddleston, R. Scott Dunbar, Michael H. Freilich, Frank J. Wentz, W. Linwood Jones
Faculty Publications
Scatterometer instruments are active microwave sensors that transmit a series of microwave pulses and measure the returned echo power to determine the normalized radar backscattering cross section (sigma-0) of the ocean surface from which the speed and direction of near-surface ocean winds are derived. The NASA Scatterometer (NSCAT) was launched on board the ADEOS spacecraft in August 1996 and returned ten months of high-quality data before the failure of the ADEOS spacecraft terminated the data stream in June 1997. The purpose of this paper is to provide an overview of the NSCAT instrument and sigma-0 computation and to describe the …
Cryosphere Applications Of Nscat Data, David G. Long, Mark R. Drinkwater
Cryosphere Applications Of Nscat Data, David G. Long, Mark R. Drinkwater
Faculty Publications
Though designed to measure vector winds over the ocean, new imaging techniques facilitate the use of NASA scatterometer data (NSCAT) in cryosphere studies. NSCAT provides data of unprecedented coverage, resolution, and quality which, when coupled with the scatterometer image reconstruction with filtering (SIRF) algorithm, enables images of O at resolutions approaching 8 km over stationary targets. Such images are useful in ice mapping and classification, and multidecadal studies are possible by comparison with Seasat Scatterometer (SASS) data. The utility of NSCAT data in polar ice studies is illustrated through a review of two cryosphere applications of NSCAT data: (1) sea-ice …
The Probability Density Of Spectral Estimates Based On Modified Periodogram Averages, David G. Long, Paul E. Johnson
The Probability Density Of Spectral Estimates Based On Modified Periodogram Averages, David G. Long, Paul E. Johnson
Faculty Publications
Welch's (1967) method for spectral estimation of averaging modified periodograms has been widely used for decades. Because such an estimate relies on random data, the estimate is also a random variable with some probability density function. Here, the PDF of a power estimate is derived for an estimate based on an arbitrary number of frequency bins, overlapping data segments, amount of overlap, and type of data window, given a correlated Gaussian input sequence. The PDFs of several cases are plotted and found to be distinctly non-Gaussian (the asymptotic result of averaging frequency bins and/or data segments), using the Kullback-Leibler distance …
Online Auctions, Michael N. Huhns, José M. Vidal
Online Auctions, Michael N. Huhns, José M. Vidal
Faculty Publications
Auctions on the Internet can involve not only consumers, but also businesses. They can form dynamically and enable the exchange of goods much as stock exchanges manage the buying and selling of securities. But because auctions have a wide scope and a short lifetime, the opportunistic behavior needed for successful interaction requires agents to both participate in and manage auctions. The article focuses on the use of software agents in such Internet based auctions
Portfolio Assessment In Aerodynamics, Nikos J. Mourtos
Portfolio Assessment In Aerodynamics, Nikos J. Mourtos
Faculty Publications
A new way of assessing student learning in an aerodynamics course through the use of portfolios is presented. The approach is portable to any engineering course, with a few modifications depending on content. The main idea is to allow students more responsibility for their own learning. Instead of having everyone in the class perform identical activities (homework, experiments, projects, tests, etc.), a cadre of assignments is made available to them. Students choose and perform (within reason) the ones that suit them better in terms of their own strengths and learning styles. The ultimate goal is for each student to demonstrate …
The Probability Distribution Of Nscat Measurements, Paul E. Johnson, David G. Long
The Probability Distribution Of Nscat Measurements, Paul E. Johnson, David G. Long
Faculty Publications
NSCAT makes only indirect measurements of wind. The direct measurement is of the backscattered radar power. The signal power is contaminated by radiometric noise so a separate measurement of the noise power is subtracted from the signal-plus-noise measurement to estimate the backscattered power. Using the radar equation, sigma-0 is computed from the measured signal power. From multiple sigma-0 mesaurements made at different azimuth angles, the wind is estimated. In wind retrieval, the NSCAT sigma-0 measurements are assumed to have a Gaussian probability distribution with a variance which depends on the mean. Given this distribution model, the maximum-likelihood estimtor is formed …
Observations Of Lattice Curvature Near The Interface Of A Deformed Aluminium Bicrystal, Brent L. Adams, W. E. King, S. Sun
Observations Of Lattice Curvature Near The Interface Of A Deformed Aluminium Bicrystal, Brent L. Adams, W. E. King, S. Sun
Faculty Publications
This work was partially supported by MRSEC Program of the National Science Foundation (DMR-9632556), and under the auspices of the US Department of Energy and Lawrence Livermore National Laboratory under contract W-7405- Eng-48. S. Sun gratefully acknowledges the comments of Professor E. T. Onat, Professor B. T. Chu and Professor W. Tong of the Mechanical Engineering Department at Yale University, and their valuable guidance in the process of completing this project as a doctoral dissertation. The assistance of B. El-Dasher of Carnegie-Mellon University is also gratefully acknowledged. Reported here is a study of the pattern of lattice curvature near the …
Constructions Of Generalized Concatenated Codes And Their Trellis-Based Decoding Complexity, Robert H. Morelos-Zaragoza, Toru Fujiwara, Tadao Kasami, Shu Lin
Constructions Of Generalized Concatenated Codes And Their Trellis-Based Decoding Complexity, Robert H. Morelos-Zaragoza, Toru Fujiwara, Tadao Kasami, Shu Lin
Faculty Publications
In this correspondence, constructions of generalized concatenated (GC) codes with good rates and distances are presented. Some of the proposed GC codes have simpler trellis omplexity than Euclidean geometry (EG), Reed–Muller (RM), or Bose–Chaudhuri–Hocquenghem (BCH) codes of approximately the same rates and minimum distances, and in addition can be decoded with trellis-based multistage decoding up to their minimum distances. Several codes of the same length, dimension, and minimum distance as the best linear codes known are constructed.
Determination Of A Methane Intermolecular Potential Model For Use In Molecular Simulations From Ab Initio Calculations, Richard L. Rowley, Tapani A. Pakkanen
Determination Of A Methane Intermolecular Potential Model For Use In Molecular Simulations From Ab Initio Calculations, Richard L. Rowley, Tapani A. Pakkanen
Faculty Publications
The possibility of obtaining an accurate site-site potential model suitable for use in molecular dynamics (MD) simulations of methane from ab initio calculations has been explored. Counterpoise-corrected (CPC), supermolecule, ab initio energies at the MP2/6-311 + G(2df,2pd) level were computed for eleven relative orientations of two methane molecules as a function of C-C separation distance. C-C, C-H, and H-H interaction parameters in a pairwise-additive, site-site potential model for rigid methane molecules were regressed from the ab initio energies, and the resultant model accurately reproduced the ab initio energies. The model suggests that C-H attractions are dominant in weakly binding the …
A Decision-Oriented Framework For Evaluating Deployment Strategies For Intelligent Transportation Systems, H.-S. Jacob Tsao
A Decision-Oriented Framework For Evaluating Deployment Strategies For Intelligent Transportation Systems, H.-S. Jacob Tsao
Faculty Publications
Because Intelligent Transportation Systems (ITS) R&D is performed for the ultimate deployment in the real world, deployment issues may limit design options for ITS concepts and technologies and, hence, can be viewed as constraints on ITS R&D. Therefore, ITS deployment issues must be studied at the outset of the R&D process. This paper develops a framework to help recognize and organize such issues. The findings can be used by ITS researchers in developing deployable ITS concepts and technologies and by ITS promoters in deploying ITS technologies having been developed already. Based on a focus on decisions impacting the deployment of …
Spatial And Temporal Factors In Estimating The Potential Of Ride-Sharing For Demand Reduction, H.-S. Jacob Tsao, Da-Jie Lin
Spatial And Temporal Factors In Estimating The Potential Of Ride-Sharing For Demand Reduction, H.-S. Jacob Tsao, Da-Jie Lin
Faculty Publications
Traffic congestion has been a pervasive problem in many urban areas of this country. This paper studies the potential of carpooling among unrelated partners (i.e., inter-household carpooling) for demand reduction during peak commute hours. Basic questions about this potential include the following. Can the current population density, origin-destination distribution, tolerable pick-up and drop-off delays, departure time distribution, and the tolerance for deviation from preferred departure time support a sizable carpooling population that can make a significant contribution to traffic demand reduction? Could the proportion of long trips that are likely candidates for carpooling (e.g., those long trips with same O-D) …
Networking Embedded Agents, Michael N. Huhns
Networking Embedded Agents, Michael N. Huhns
Faculty Publications
Most of us will soon be managing an intranet in our homes, though we might not realize it. We might also be surprised at the devices that will be networked together. Just about every electrical device now contains one or more microprocessors. Designers typically find this a cost-effective way to provide device functionality, even when much of a processor's power is unnecessary or unused. For example, my coffee maker contains a processor, even though the appliance needn't be very smart and wastes most of its CPU cycles. Nevertheless, it is cheaper to include a general-purpose microprocessor than to incorporate custom …
Personal Ontologies, Michael N. Huhns, Larry M. Stevens
Personal Ontologies, Michael N. Huhns, Larry M. Stevens
Faculty Publications
Corporations can suffer from too much information, and it is often inaccessible, inconsistent, and incomprehensible. The corporate solution entails knowledge management techniques and data warehouses. The paper discusses the use of the personal ontology. The promising approach is an organization scheme based on a model of an office and its information, an ontology, coupled with the proper tools for using it.
Correlation Of Double-Layer Capacitance With The Pore Structure Of Sol-Gel Derived Carbon Xerogels, Chuan Lin, James A. Ritter, Branko N. Popov
Correlation Of Double-Layer Capacitance With The Pore Structure Of Sol-Gel Derived Carbon Xerogels, Chuan Lin, James A. Ritter, Branko N. Popov
Faculty Publications
Nine different sol-gel derived carbon xerogels were prepared with different pore structures by varying the carbonization temperature (in flowing N2) and activation time (in 5% CO2 in N2). For each of these carbon xerogels, mesopore and micropore size distributions and cumulative surface areas were extracted from a density functional theory analysis. Increasing the carbonization temperature caused a decrease in the number of micropores in the 6 Å range but had little effect on the mesopore size distribution and thus mesopore cumulative surface area. Increasing the CO2 activation time caused an increase in the number …
Development And Application Of A Correlation Of 13c Nmr Chemical Structural Analyses Of Coal Based On Elemental Composition And Volatile Matter Content, Dominic Genetti, Thomas H. Fletcher, Ronald J. Pugmire
Development And Application Of A Correlation Of 13c Nmr Chemical Structural Analyses Of Coal Based On Elemental Composition And Volatile Matter Content, Dominic Genetti, Thomas H. Fletcher, Ronald J. Pugmire
Faculty Publications
13C NMR spectroscopy has been shown to be an important tool in the characterization of coal structure. Important quantitative information about the carbon skeletal structure is obtained through 13C NMR spectral analysis of coal. Solid-state 13C NMR analysis techniques have progressed beyond the mere determination of aromaticity and can now describe features such as the number of aromatic carbons per cluster and the number of attachments per aromatic cluster. These 13C NMR data have been used to better understand the complicated structure of coal, to compare structural differences in coal, tar, and char, and to model …
Modeling Nitrogen Release During Devolatilization On The Basis Of Chemical Structure Of Coal, Dominic Genetti, Thomas H. Fletcher
Modeling Nitrogen Release During Devolatilization On The Basis Of Chemical Structure Of Coal, Dominic Genetti, Thomas H. Fletcher
Faculty Publications
A model that predicts the amount and distribution between tar and light gas of nitrogen released during devolatilization has been developed and incorporated into the chemical percolation devolatilization (CPD) model. This work represents the first volatile nitrogen release model developed on the basis of 13C NMR measurements of coal structure. This work also represents the first volatile nitrogen release model evaluated by comparing model predictions with chemical structural features of the char (determined by 13C NMR spectral analyses). The model is limited to nitrogen release during primary pyrolysis, and assumes that all light-gas nitrogen is HCN. Model predictions …
Micropolarizer Array For Infrared Imaging Polarimetry, M. W. Jones, Gregory P. Nordin, P. C. Deguzman, J. T. Meier
Micropolarizer Array For Infrared Imaging Polarimetry, M. W. Jones, Gregory P. Nordin, P. C. Deguzman, J. T. Meier
Faculty Publications
The design and fabrication of a micropolarizer array for imaging polarimetry is described for the 3–5-μm-wavelength region. Each micropolarizer consists of a 475-nm-period Mo wire grid in a 16 μm × 16 μm aperture. Interference lithography is used to generate the small grating features through an etch mask layer. Arrays of 256 × 256 micropolarizers at three distinct angular orientations have been fabricated that permit the measurement of the first three Stokes vector components in each pixel of an imaging polarimeter. An imaging system composed of a micropolarizer array integrated directly onto a focal plane array has been assembled, and …
Spin-Up In A Tank Induced By A Rotating Bluff Body, R. Daniel Maynes, J. Klewicki, P. Mcmurty
Spin-Up In A Tank Induced By A Rotating Bluff Body, R. Daniel Maynes, J. Klewicki, P. Mcmurty
Faculty Publications
Spin-up of a turbulent flow in a cylindrical tank caused by a rotating bluff body has been investigated using flow visualization, fluid velocity measurements, and hydrodynamic torque measurements. During the spin-up process three distinct temporal regimes exist. These regimes are: (i) a build-up regime where the torque and the tangential velocity fluctuations in the close proximity of the body remain constant; (ii) a decay regime where these quantities decay with power-law relations; and (iii) a mean flow steady state where these values remain relatively constant. Experiments were conducted in two tanks differing in volume by a factor of 80 and …