Engineering Commons^™

Conversion Of Coal Tar To Soot During Coal Pyrolysis In A Post-Flame Environment, Thomas H. Fletcher, Jinliang Ma, Brent W. Webb

Faculty Publications

Coal pyrolysis experiments were performed in the postflame region of a CH4/H2/air flat-flame burner operating under fuel-rich conditions, where the temperature and gas compositions were similar to those in the near-burner region of a large-scale coal-fired furnace. Volatiles released from the coal particles formed a cloud of soot particles at high temperatures in the absence of oxygen. The soot particles in the cloud were collected at different residence times using a water-cooled, nitrogen-quenched suction probe. Test variables included the reaction temperature and coal type. Soot yields in terms of weight percentage of dry ash-free coal were measured based on bulk …

A Computational Method For Determining Global Fuel-No Rate Expressions. Part 1, Wei Chen, L Douglas Smoot, Thomas H. Fletcher, Richard D. Boardman

Faculty Publications

Global chemical reaction rates used in the modeling of NO_x formation in comprehensive combustion codes have traditionally been obtained through correlation of experimental data. In this paper, a computational approach for obtaining global rates is presented. Several premixed flames were simulated, and sensitivity analysis of species concentration profiles was used to suggest global pathways in fuel-nitrogen conversion to NO. Based on these analyses, the global reaction rates were formulated. The predicted species concentration profiles and their derivatives were then used in the determination of the global rate constants. The correlation of rate constants for the two fuel-NO global rates …

Combustion Modeling Of Rdx, Hmx And Gap With Detailed Kinetics, Jeffrey E. Davidson

Theses and Dissertations

A one-dimensional, steady-state numerical model of the combustion of homogeneous solid propellant has been developed. The combustion processes is modeled in three regions: solid, two-phase (liquid and gas) and gas. Conservation of energy and mass equations are solved in the two-phase and gas regions and the eigenvalue of the system (the mass burning rate) is converged by matching the heat flux at the interface of these two regions. The chemical reactions of the system are modeled using a global kinetic mechanism in the two-phase region and an elementary kinetic mechanism in the gas region. The model has been applied to …

Chen, W., L. D. Smoot, S. C. Hill, And T. H. Fletcher, “Global Rate Expression For Nitric Oxide Reburning. Part 2,” Energy And Fuels, 10, 1046-1052 (1996)., Wei Chen, L Douglas Smoot, Scott C. Hill, Thomas H. Fletcher

Faculty Publications

An investigation of a global reburning-NO reaction, sum(C_iH_j) + NO => HCN + . . ., which is a reduction pathway of nitric oxide (NO) by reaction with gaseous hydrocarbons, was conducted. The global reburning-NO rate expression was deduced from a combination of elemental reactions. The global rate expression and its rate constants were then determined by correlating predicted species profiles from simple hydrocarbon flames. This global reburning-NO rate constant can be expressed as 2.7x10⁶ exp(-18,800/RT) (gmol/cm³ s). This expression and constants are applicable to atmospheric pressure with an equivalence ratio range of 1.0-2.08 …

Effects Of Pyrolysis Heating Rate On Intrinsic Reactivities Of Coal Chars, Thomas K. Gale, Calvin H. Bartholomew, Thomas H. Fletcher

Faculty Publications

The main objective of this work was to determine the effects of pyrolysis heating rate on intrinsic O₂ reactivity of coal chars. Relationships of intrinsic reactivity to other pyrolysis conditions and char physical and chemical structure were also investigated, and empirical correlations were obtained. Two different entrained flow reactors (a flat flame methane/air burner and a drop tube reactor) were used to prepare chars under a variety of different pyrolysis conditions at maximum particle temperatures and heating rates of 840-1627 K and 10⁴ to 2x10⁵ K/s, respectively. Intrinsic reactivities of a lignite and two bituminous coal chars …

Kinetic Analysis Of The Fate Of Nitric Oxide Synthesized By Macrophages In Vitro, Randy S. Lewis, Snait Tamir, Steven R. Tannenbaum, William M. Deen

Faculty Publications

To investigate the fate of nitric oxide (NO) synthesized by activated macrophages, the concentrations of NO and its principal reaction products, nitrite (NO2-) and nitrate (NO3-), were measured as a function of time in suspension cultures of RAW264.7 macrophages attached to microcarrier beads. Synthesis of NO became evident 2-5 h after stimulation of the cells, and steady concentrations of NO were achieved after about 9 h. The appearance of NO in the extracellular fluid coincided with the appearance of NO2- and NO3-, which were formed thereafter at approximately equal and constant rates. Using a kinetic model based on rate constants …

A Massively Parallel Computation Strategy For Fdtd: Time And Space Parallelism Applied To Electromagnetics Problems, Michael A. Jensen, Amir Fijany, Yahya Rahmat-Samii, Jacob Barhen

Faculty Publications

We present a novel strategy for incorporating massive parallelism into the solution of Maxwell's equations using finite-difference time-domain methods. In a departure from previous techniques wherein spatial parallelism is used, our approach exploits massive temporal parallelism by computing all of the time steps in parallel. Furthermore, in contrast to other methods which appear to concentrate on explicit schemes such as Yee's (1966) algorithm, our strategy uses the implicit Crank-Nicolson technique which provides superior numerical properties. We show that the use of temporal parallelism results in algorithms which offer a massive degree of coarse grain parallelism with minimum communication and synchronization …

Integrating Reconstructed Scatterometer And Advanced Very High Resolution Radiometer Data For Tropical Forest Inventory, David G. Long, Perry J. Hardin

Faculty Publications

A scientific effort is currently underway to assess tropical forest degradation and its potential impact on Earth's climate. Because of the large continental regions involved, Advanced Very High Resolution Radiometer (AVHRR) imagery and its derivative vegetation index products with resolutions between 1 and 12 km are typically used to inventory the Earth's equatorial vegetation. Archival AVHRR imagery is also used to obtain a temporal baseline of historical forest extent. Recently however, 50-km Seasat-A Scatterometer (SASS) Ku-band imagery (acquired in 1978) has been reconstructed to = 4-km resolution, making it a supplement to AVHRR imagery for historical vegetation assessment. In order …

A Pixel Scale Digital-To-Analog Converter Array For Liquid Crystal On Vlsi Displays, Gregory P. Nordin, S. T. Kowel, J. H. Kulick, R. G. Lindquist, P. J. Nasiatka, A. Thomsen

Faculty Publications

A pixel scale digital to analog converter and driver for liquid crystal (LC) cells is presented. The circuit is a compact CMOS logic gate that sums pulse density modulation (pdm) signals. Low pass filtering of the pdm signal is 'done by the LC material. The circuit is suitable to implement large arrays of converters as, for example, in display applications. It is applicable in LC on silicon displays where gray scale data are stored and converted at each pixel site. Advantages over the commonly used active matrix technology include the removal of all analog circuitry, no need for refresh, reduced …

Electromagnetic Boundary Conditions And Differential Forms, Karl F. Warnick, Richard H. Selfridge, David V. Arnold

Faculty Publications

A new representation for electromagnetic boundary conditions involving a boundary projection operator defined using the interior and exterior products of the calculus of differential forms is developed. This operator expresses boundary conditions for fields represented by differential forms of arbitrary degree. With vector analysis, the field intensity boundary conditions require the cross product, whereas the flux boundary conditions use the inner product. With differential forms, the field intensity and flux density boundary conditions are expressed using a single operator. This boundary projection operator is readily applied in practice, so that this work extends the utility of the calculus of differential …

Liquid Crystal-On-Silicon Implementation Of The Partial Pixel Three-Dimensional Display Architecture, M. W. Jones, Gregory P. Nordin, M. Friends, S. T. Kowel, J. H. Kulick, R. G. Lindquist, P. J. Nasiatka

Faculty Publications

We report the implementation of a liquid crystal-on-silicon, three-dimensional 13-D2 diffractive display based on the partial pixel architecture. The display generates multiple stereoscopic images that are perceived as a static 3-D scene with one-dimensional motion parallax in a manner that is functionally equivalent to a holographic stereogram. The images are created with diffraction gratings formed in a thin liquid crystal layer by fringing electric fields from transparent indium tin oxide interdigitated electrodes. The electrodes are controlled by an external drive signal that permits the 3-D scene to be turned on and off. The display has a contrast ratio of 5.8, …

Real-Time Three-Dimensional Display Based On The Partial Pixel Architecture, Gregory P. Nordin, M. W. Jones, S. T. Kowel, J. H. Kulick, R. G. Lindquist

Faculty Publications

We previously reported several static three-dimensional (3-D) display implementations of the partial pixel architecture [J. Opt. Soc. Am. A 12, 73 (1995)]. We report herein our f irst real-time 3-D display based on this architecture. The display is functionally equivalent to a real-time holographic stereogram. It is autostereoscopic and provides horizontal motion parallax. The display device is composed of a diffractive optical element (fabricated with standard photolithographic techniques) and a separate conventional liquidcrystal display. The display has been used to play back a precomputed animated 3-D scene at video frame rates using a standard VGA video output.

Pulse Width Modulation Drive Technique For High Resolution Liquid Crystal Gratings, Gregory P. Nordin, S. T. Kowel, J. H. Kulick, R. G. Lindquist, P. J. Nasiatka, A. Thomsen

Faculty Publications

We report the use of a pulse-width modulation drive technique for high-resolution liquid-crystal gratings and show how the grating diffraction efficiency depends on the duty cycle of the drive signal. We identify a regime in which the diffraction efficiency is linearly proportional to the duty cycle, thereby providing a linear drive characteristic.

Otter: A Testbed Submersible For Robotics Research, Tim Mclain, H H. Wang, R L. Marks, S D. Fleischer, D W. Miles, G A. Sapilewski, S M. Rock, M J. Lee, R C. Burton

Faculty Publications

Untethered, unmanned submersibles (UUSs) have the potential of becoming useful tools in nuclear reactor inspection and repair and waste-site cleanup and survey, in addition to subsea exploration. Classical "hand-in-glove" control methods used currently by tethered, remotely-operated vehicles (ROVs) are unsuitable for UUS systems which have, at best, limited communications. The Stanford Aerospace Robotics Laboratory (ARL) has joined with the Monterey Bay Aquarium Research Institute (MBARI) in a program to develop new methods of controlling UUS systems.

As a part of this effort, a submersible testbed has been built to test and develop new technologies that will make UUSs useful tools …

Effects Of Pyrolysis Conditions On Internal Surface Areas And Densities Of Coal Chars Prepared At High Heating Rates In Reactive And Non-Reactive Atmospheres, Thomas K. Gale, Thomas H. Fletcher, Calvin H. Bartholomew

Faculty Publications

Concern about comparability and validity of different methods for producing coal chars for reactivity experiments has led to research on the effect of devolatilization conditions on the char physical and chemical structure. Particle diameter and porosity changes during devolatilization significantly affect char oxidation rates. In particular, physical properties of chars prepared in drop tube reactors differ greatly from chars prepared in fiat flame burner experiments. Recent data indicate that the presence of oxygen in the gas atmosphere has no effect on swelling until char oxidation has begun. The present research concentrates on the effects of heating rate, particle temperature and …

Em Interaction Of Handset Antennas And A Human In Personal Communications, Michael A. Jensen, Yahya Rahmat-Samii

Faculty Publications

In personal communications, the electromagnetic interaction between handset-mounted antennas and the nearby biological tissue is a key consideration. This paper presents a thorough investigation of this antenna-tissue interaction using the finite-difference time-domain (FDTD) electromagnetic simulation approach with detailed models of real-life antennas on a transceiver handset. The monopole, side-mounted planar inverted F, top-mounted bent inverted F, and back-mounted planar inverted F antennas are selected as representative examples of external and internal configurations. Detailed models of the human head and hand are implemented to investigate the effects of the tissue location and physical model on the antenna performance. Experimental results are …

Study Of The Time Efficiency And Volume Of Wood Used For Three Types Of Stove In The Salitrón Community Of San Juan Ermita, Department Of Chiquimula, Fredy Samuel Coronado López

Theses and Dissertations

In developing countries such as Guatemala, firewood is increasingly being used for cooking in most rural areas. Consequently, there is a shortage of firewood in these areas beca use trees do not grow at the same rate as they are consumed. Some authors report that 90% of the heat from firewood is lost during combustion. Several alternatives to open pit fires exist to reduce the amount of firewood used. However, these alternatives need to be evaluated to determine their efficiency. This project compared the time efficiency and volume of firewood used in the Finlandia style improved stoves, Josefina stoves, and …

Partial Pixels: A Three-Dimensional Diffractive Display Architecture, Gregory P. Nordin, M. W. Jones, S. T. Kowel, J. H. Kulick, R. G. Lindquist, P. J. Nasiatka, A. Parker

Faculty Publications

We describe in detail the partial pixel architecture that permits the realization of three-dimensional (3-D) displays that are functionally equivalent to a real-time holographic stereogram. This architecture permits the simultaneous presentation of multiple stereoscopic images so that motion parallax is discernible in the resultant 3-D scene. The key innovation of the architecture is that each pixel is subdivided into partial pixels, which in turn can be implemented as individual diffraction gratings. We describe a static display that exhibits a 3-D image with one-dimensional motion parallax, thereby demonstrating key features of the architecture. A variety of partial pixel implementations are discussed …

Decreases In The Swelling And Porosity Of Bituminous Coals During Devolatilization At High Heating Rates, Thomas K. Gale, Thomas H. Fletcher, Calvin H. Bartholomew

Faculty Publications

Concern about comparability and validity of different methods for producing coal chars for reactivity experiments has led to research on the effect of devolatilization conditions on the char physical and chemical structure. Particle diameter and porosity changes during devolatilization significantly affect char oxidation rates. In particular, physical properties of chars prepared in drop tube reactors differ greatly from chars prepared in flat flame burner experiments. Recent data indicate that the presence of oxygen in the gas atmosphere has no effect on swelling until char oxidation has begun. The present research concentrates on the effects of heating rate, particle temperature and …

Thermophoretic Sampling Of Coal-Derived Soot Particles During Devolatilization, Jinliang Ma, Thomas H. Fletcher, Brent W. Webb

Faculty Publications

Thermophoretic sampling of soot particles formed during high-temperature coal devolatilization is performed in order to examine soot particle sizes and shapes. Coal particles are injected along the centerline of a laminar flow flat flame burner, where a fuel-rich methane-air flame is used as a heat source. Volatiles released from the coal particles form a cloud of soot particles at high temperatures in the absence of oxygen. A carbon-coated microscope grid is briefly inserted into the soot cloud, where the temperature gradient between the soot particles and the cold grid surface causes the migration of soot particles and results in deposition. …

Ultrasonic Enhancement Of Antibiotic Action On Gram-Negative Bacteria, William G. Pitt, Michael O. Mcbride, Jared K. Lunceford, Randall J. Roper, Richard D. Sagers

Faculty Publications

The effect of gentamicin upon planktonic cultures of Pseudomonas aeruginosa, Escherichia coli, Staphylococcus epidermidis, and Staphylococcus aureus was measured with and without application of 67-kHz ultrasonic stimulation. The ultrasound was applied at levels that had no inhibitory or bactericidal activity against the bacteria. Measurements of the MIC and bactericidal activity of gentamicin against planktonic cultures of P. aeruginosa and E. coli demonstrated that simultaneous application of 67-kHz ultrasound enhanced the effectiveness of the antibiotic. A synergistic effect was observed and bacterial viability was reduced several orders of magnitude when gentamicin concentrations and ultrasonic levels which by themselves did not reduce …

Characterization Of The Near-Interface Region Of Chemical Vapor Deposited Diamond Films On Silicon By Backscatter Kikuchi Diffraction, Brent L. Adams, K. Kunze, S. Geier, R. Hessmer, M. Schreck, B. Rauschembach, B. Stritzker

Faculty Publications

The lattice orientations near the interface of chemical vapor deposited diamond films on Si(001) have been studied by orientation imaging microscopy. This technique is based on the automated analysis of electron backscatter Kikuchi diffraction patterns. The electron beam has been scanned in discrete steps over the reverse side of the diamond film after having removed the substrate. The obtained data have allowed us to determine the texture and to visualize quantitatively the orientational arrangement of and among individual diamond crystallites in the near-interface region. A comparison with the orientation of the substrate has proved the existence of epitaxially nucleated grains. …

Polynomial Real Root Finding In Bernstein Form, Melvin R. Spencer

Theses and Dissertations

This dissertation addresses the problem of approximating, in floating-point arithmetic, all real roots (simple, clustered, and multiple) over the unit interval of polynomials in Bernstein form with real coefficients.

Performance Analysis Of Antennas For Hand-Held Transceivers Using Fdtd, Michael A. Jensen, Yahya Rahmat-Samii

Faculty Publications

The design of antennas for hand-held communications devices depends on the implementation of simulation tools that can accurately model general topologies. The paper presents the analysis of small antennas mounted on hand-held transceivers using the finite-difference time-domain (FDTD) method. The key features of the FDTD implementation are discussed, with particular emphasis placed upon modeling of the source region. The technique is used to predict the gain patterns and broadband input impedance behavior of monopole, planar inverted F, and loop antenna elements mounted on the handset. Effects of the conducting handset chassis, the plastic casing around the device, and lumped elements …

Characterization Of The Near-Interface Region Of Chemical Vapor Deposited Diamond Films On Silicon By Backscatter Kikuchi Diffraction, Brent L. Adams, K. Kunze, S. Geier, R. Hessmer, B. Rauschembach, M. Schreck, B. Stritzker

Faculty Publications

B.L.A. and K.K. gratefully acknowledge support under a Materials Research Group Award by the National Science Foundation No. DMR-9001278. Also the software support by Th. Bollmeier is greatly appreciated. The lattice orientations near the interface of chemical vapor deposited diamond films on Si(001) have been studied by orientation imaging microscopy. This technique is based on the automated analysis of electron backscatter Kikuchi diffraction patterns. The electron beamhas been scanned in discrete steps over the reverse side of the diamond film after having removed the substrate. The obtained data have allowed us to determine the texture and to visualize quantitatively the …

Inversion Of Light Scattering Measurements For Particle Size And Optical Constants: Theoretical Study, Matthew R. Jones, Bill P. Curry, M. Quinn Brewster, Keng H. Leong

Faculty Publications

We invert the Fredholm equation representing the light scattered by a single spherical particle or a distribution of spherical particles to obtain the particle size distribution function and refractive index. We obtain the solution by expanding the distribution function as a linear combination of a set of orthonormal basis functions. The set of orthonormal basis functions is composed of Schmidt-Hilbert eigenfunctions and a set of supplemental basis functions, which have been orthogonalized with respect to the Schmidt-Hilbert eigenfunctions by using the Gram-Schmidt orthogonalization procedure. We use the orthogonality properties of the basis functions and of the eigenvectors of the kernel …

Inversion Of Light Scattering Measurements For Particle Size And Optical Constants: Experimental Study, Matthew R. Jones, Keng H. Leong, M. Quinn Brewster, Bill P. Curry

Faculty Publications

Measurements of the light scattered by a sample contain information regarding the physical properties of the sample. Laser light-scattering measurements can be made unobtrusively in environments that are inaccessible to other types of measurements, so laser light-scattering techniques have become an important tool in aerosol research. The primary difficulty associated with using light-scattering techniques to determine aerosol particle properties is inverting the measurements or extracting the desired information from the measurements. In this study we use a 15-channel polar nephelometer to measure the light-scattering patterns of monodisperse polystyrene spheres. The light-scattering measurements are inverted, and the particle size distribution function …

Demonstration Of A Novel 3-D Autostereoscopic Display, M. W. Jones, Gregory P. Nordin, S. T. Kowel, J. H. Kulick, R. G. Lindquist, P. J. Nasiatka

Faculty Publications

We report what we believe is the first static implementation of the partial-pixel architecture, which provides a conceptual framework for the construction of real-time three-dimensional displays that are functionally equivalent to holographic stereograms (i.e., the simultaneous display of a series of stereoscopic images). The device is physically realized as a set of amplitude diffraction gratings on a chrome mask that was fabricated by standard photolithographic techniques. The intended three-dimensional object encoded in the display was strikingly visible on readout with an incoherent illumination source.

High Resolution Liquid Crystal Phase Grating Formed By Fringing Fields From Interdigitated Electrodes, Gregory P. Nordin, M. Friends, J. M. Jarem, S. T. Kowel, J. H. Kulick, T. Leslie, R. G. Lindquist

Faculty Publications

We report the formation of thin anisotropic phase gratings in a nematic liquid-crystalline film by use of lateral (fringing) electric fields induced by transparent interdigitated electrodes. These gratings yield high diffraction efficiency (>30%) with a strong dependence on the readout beam incidence angle. In addition, the formation of a defect wall is observed that has a significant effect on the diffraction properties of the phase grating.

Characterization Of Electromagnetically Coupled Superquadric Loop Antennas For Mobile Communications Applications, Michael A. Jensen, Yahya Rahmat-Samii

Faculty Publications

Analysis of two mutually coupled loop antennas with arbitrary relative orientation and position and possibly different geometries is presented. The antennas are represented by generalised superquadric curves, which include circular, elliptical, and rectangular loop geometries, and they may be located either in a homogeneous region or next to an infinite ground plane. A Galerkin-type moment method with piecewise sinusoidal subsectional basis and weighting functions is used. Special consideration is given to implement the solution using curved wire segments instead of the commonly employed linear segments to improve computational efficiency. This very general computational tool is used to investigate the behaviour …