Engineering Commons^™

California Crop And Soil Evapotranspiration, Charles Burt

BioResource and Agricultural Engineering

The goal of this publication is to provide water users, consultants, water agency personnel, and others throughout California with information that will: (a) help individual water users with irrigation scheduling and system design and (b) help agricultural water agency personnel with water balances and future planning.

The tables in this publication represent the consolidation of results from thousands of annual ET simulations that accounted for crop, rainfall (wet, dry, or “typical”), soil, and irrigation method in each of 13 major ETo zones in California. The annual simulations used daily water balances at the soil surface, crop canopy, and soil root …

Winter/Spring 2003, 90.9 Wmpg Fm

WMPG Program Guides

Newspaper format

Sizes And Shapes Of 10-Ma Distal Fall Pyroclasts In The Ogallala Ggroup, Nebraska, William I. Rose, C. M. Riley, S. Dartevelle

Department of Geological and Mining Engineering and Sciences Publications

Size distributions of distal ashfall particles from correlated 10-Ma layers in Nebraska, measured using laser diffraction methods, are lognormal with mode diameters of ∼90 mm. This ashfall is ∼100% bubble-wall shards of rhyolite glass and apparently represents a distal ashfall from an eruption 1400 km away. Measured terminal velocities of these ash particles are 0.2–18 cm/s, consistent with Stokes Law settling of spherical particles with diameters of 9–50 mm. Surface area of the ash particles, measured with gas adsorption, is 20–30 times the surface area of equivalent Stokes spheres. These results highlight the effects of shape and atmospheric drag in …

Quantitative Shape Measurements Of Distal Volcanic Ash, William I. Rose, Colleen M. Riley, Gregg J. Bluth

Department of Geological and Mining Engineering and Sciences Publications

Large-scale volcanic eruptions produce fine ash (< 200 μm) which has a long atmospheric residence time (1 hour or more) and can be transported great distances from the volcanic source, thus, becoming a hazard to aircraft and public health. Ash particles have irregular shapes, so data on particle shape, size, and terminal velocities are needed to understand how the irregular-shaped particles affect transport processes and radiative transfer measurements. In this study, a methodology was developed to characterize particle shapes, sizes , and terminal velocities for three ash samples of different compositions. The shape and size of 2,500 particles from 1) distal fallout (~100 km) of the October 14, 1974 Fuego eruption (basaltic), 2) the secondary maxima (~250 km) of the August 18, 1992 Spurr eruption (andesitic), and 3) the Miocene Ash Hollow member, Nebraska (rhyolitic) were measured using image analysis techniques. Samples were sorted into 10 to 19 terminal velocity groups (0.6-59.0 cm/s) using an air elutriation device. Grain size distributions for the samples were measured using laser diffraction. Aspect ratio, feret diameter, and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity. These measurement values show particle shape differs greatly from a sphere (commonly used in models and algorithms). The diameters of ash particles were 10-120% larger than ideal spheres at the same terminal velocity, indicating that irregular particle shape greatly increases drag. Gas-adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry, indicating that particle shapes are highly irregular. Correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values.

Retrieval Of Mass And Sizes Of Particles In Sandstorms Using Two Modis Ir Bands: A Case Study Of April 7 2001 Sandstorm In China, Yingxin Gu, William I. Rose, Gregg J. Bluth

Department of Geological and Mining Engineering and Sciences Publications

A thermal infrared remote sensing retrieval method developed by Wen and Rose [1994], which retrieves particle sizes, optical depth, and total masses of silicate particles in the volcanic cloud, was applied to an April 07, 2001 sandstorm over northern China, using MODIS. Results indicate that the area of the dust cloud observed was 1.34 million km2, the mean particle radius of the dust was 1.44 μm, and the mean optical depth at 11 μm was 0.79. The mean burden of dust was approximately 4.8 tons/km2 and the main portion of the dust storm on April 07, 2001 contained 6.5 million …

Reynolds-Stress Turbulence Model In The Kiva Code For Engine Simulation, Yeow-Khern Siow

Dissertations, Master's Theses and Master's Reports - Open

A Reynolds-Stress Turbulence Model has been incorporated with success into the KIVA code, a computational fluid dynamics hydrocode for three-dimensional simulation of fluid flow in engines. The newly implemented Reynolds-stress turbulence model greatly improves the robustness of KIVA, which in its original version has only eddy-viscosity turbulence models. Validation of the Reynolds-stress turbulence model is accomplished by conducting pipe-flow and channel-flow simulations, and comparing the computed results with experimental and direct numerical simulation data. Flows in engines of various geometry and operating conditions are calculated using the model, to study the complex flow fields as well as confirm the model’s …

Development And Evaluation Of A Tie-Down System For The Redesigned F-Shape Concrete Temporary Barrier, Karla A. Polivka, Ronald K. Faller, John R. Rohde, James C. Holloway, Bob W. Bielenberg, Dean L. Sicking

Mid-America Transportation Center: Final Reports and Technical Briefs

Often, temporary barriers are used in applications where it is desired that their deflection during vehicular impact be limited. One such application is in the installation of temporary barriers placed adjacent to the edge of a concrete bridge deck in order to maximize lane width. Acceptable tie-down systems for temporary barriers have previously been developed, but there are concerns when the barriers and tie-down systems are used on bridges that are reconstructed in stages and where very little tolerance in barrier deflection is allowable. Therefore, a rigid tie-down system was developed that minimizes barrier deflections. For this system, the original …

Complexity Of Single-Agent And Equilibrium-Based Multiagent Planning And Plan Checking: Approach When We Have A List Of Valid States, Chitta Baral, Vladik Kreinovich

Departmental Technical Reports (CS)

In a recent paper M. Bowling, R. Jensen, and M. Veloso proposed a new formalization of the problem of multiagent planning - a formalization that is based on the (intuitively natural) notion of an equilibrium. In this paper we analyze the computational complexity of the corresponding equilibrium-based multiagent planning and plan checking. Within the traditional approach in which states are described by fluents, the computational complexity of planning under incompleteness is PSPACE-hard already for a single agent; therefore, to make a meaningful comparison between the complexity of single-agent and multi-agent planning, we analyze complexity in a different approach, in which …

Long-Lasting Photoluminescence In Freestanding Gan Templates, Michael A. Reshchikov, M. Zafar Iqbal, Hadis Morkoç, S. S. Park, K. Y. Lee

Electrical and Computer Engineering Publications

We studied time-resolvedphotoluminescence(PL) over a temporal range 10−6–103 s in high-purity freestanding GaN templates. Red, yellow, green, blue, and shallow donor–acceptor emission bands can be resolved in the PLspectrum. Observation of luminescence long after the excitation is switched off is a striking feature of our study. The persistent PL observed for all above bands, except for the green band, is primarily attributed to the donor–acceptor-pair-type recombination. An unusually slow, nonexponential decay of radiative transitions from the conduction band to the shallow acceptor was also observed, pointing to some additional mechanism for the persistent PL. Possible role of the surface states …

Stimulated Emission And Ultrafast Carrier Relaxation In Algan/Gan Multiple Quantum Wells, Ü. Özgür, Henry O. Everitt, Lei He, Hadis Morkoç

Electrical and Computer Engineering Publications

Stimulated emission (SE) and ultrafast carrier relaxation dynamics were measured in two AlxGa1−xN/GaNmultiple-quantum-well(MQW) structures, grown in a Ga-rich environment with x=0.2 and 0.3, respectively. The threshold density for SE (Ith≃100 μJ/cm2) was found to be independent of x. Room-temperature, time-resolved, differential transmission measurements mapped the carrier relaxation mechanisms for above barrier energy excitation. Photoexcited carriers are observed to relax into the QWs in <1 ps, while carrier recombination times as fast as 30 ps were measured. For excitation above Ith, SE is shown to deplete carriers in the barriers through a cascaded refilling of the QW state undergoing SE. Similar behavior is seen in an Al0.3Ga0.7N/GaNMQW grown with a N-rich atmosphere, but the relaxation phenomena of all AlGaN MQWs are significantly faster than observed in InGaN MQWs of similar structure.

4h–Sic Photoconductive Switching Devices For Use In High-Power Applications, S. Doǧan, A. Teke, D. Huang, Hadis Morkoç, C. B. Roberts, J. Parish, B. Ganguly, M. Smith, R. E. Meyers, S. E. Saddow

Electrical and Computer Engineering Publications

Siliconcarbide is a wide-band-gapsemiconductor suitable for high-power high-voltage devices and it has excellent properties for use in photoconductive semiconductor switches (PCSSs). PCSS were fabricated as planar structures on high-resistivity 4H–SiC and tested at dc bias voltages up to 1000 V. The typical maximum photocurrent of the device at 1000 V was about 49.4 A. The average on-state resistance and the ratio of on-state to off-state currents were about 20 Ω and 3×1011, respectively. Photoconductivity pulse widths for all applied voltages were 8–10 ns. These excellent results are due in part to the removal of the surface damage by high-temperature H2 …

Improvement Of N-Gan Schottky Diode Rectifying Characteristics Using Koh Etching, J. Spradlin, S. Doğan, M. Mikkelson, D. Huang, L. He, D. Johnstone, Hadis Morkoç, R. J. Molnar

Electrical and Computer Engineering Publications

KOH etch was investigated as a means to improve the I–Vcharacteristics of Schottky diodes onn-type GaNgrown by molecular-beam epitaxy on sapphire, or on hydride vapor phase epitaxy templates. Atomic force microscopy images and I–Vcharacteristics are presented. After etching as-grown films in molten KOH, Schottky diodes on c-plane GaN had orders of magnitude reduction in reverse leakage current. The best devices had leakage currents less than 10−12 A (10−8 A/cm2) at −5 V, and ideality factors of 1.04. Measurements on several different sample structures indicate a correlation between surface roughness and saturation current, and an improvement in ideality …

Electric-Field-Induced Heating And Energy Relaxation In Gan, T. A. Eckhause, Ö. Süzer, Ç. Kurdak, F. Yun, Hadis Morkoç

Electrical and Computer Engineering Publications

Electric-field-induced heating is studied using noise measurements in n-type GaN grown on sapphire substrates. The measured electron temperature is found to be an order of magnitude higher than what is expected based on calculations of electron–phonon coupling via acoustic deformation potential scattering processes in GaN. The discrepancy may be explained by a large thermal boundary resistance between the GaN film and the sapphire substrate.

Current Mapping Of Gan Films By Conductive Atomic Force Microscopy, A. A. Pomarico, D. Huang, J. Dickinson, A. A. Baski, R. Cingolani, Hadis Morkoç, R. Molnar

Electrical and Computer Engineering Publications

Conductive atomic force microscopy has been used to investigate the local conductivity in hydride vapor-phase epitaxy and molecular-beam epitaxyGaN films, focusing on the effect of off-axis facet planes. We investigated two different types of samples, in which the facet planes were either present on the perimeters of as-grown islands, or on the edges of etch pits created by post-growth chemical etching. The results show that crystallographic planes tilted with respect to the c-plane growth direction show a significantly higher conductivity than surrounding areas. The n-type (or p-type) samples required a negative (or positive) sample bias for current conduction, …

Observation Of Optical Phonon Instability Induced By Drifting Electrons In Semiconductor Nanostructures, W. Liang, K. T. Tsen, Otto F. Sankey, S. M. Komirenko, K. W. Kim, V. A. Kochelap, Meng-Chyi Wu, Chong-Long Ho, Wen-Jeng Ho, Hadis Morkoç

Electrical and Computer Engineering Publications

We have experimentally proven the Cerenkov generation of optical phonons by drifting electrons in a semiconductor. We observe an instability of the polar optical phonons in nanoscale semiconductors that occurs when electrons are accelerated to very high velocities by intense electric fields. The instability is observed when the electron drift velocity is larger than the phase velocity of optical phonons and rather resembles a “sonic boom” for optical phonons. The effect is demonstrated in p–i–nsemiconductor nanostructures by using subpicosecond Raman spectroscopy.

Conductance Modulation Of Spin Interferometers, Marc Cahay, Supriyo Bandyopadhyay

Electrical and Computer Engineering Publications

We study the conductance modulation of gate controlled electron spin interferometers (also known as spin field effect transistors) based on the Rashba spin–orbit coupling effect. It is found that the modulation is dominated by Ramsauer (or Fabry-Perot) type transmission resonances rather than the Rashba effect in typical structures. These transmission resonances are due to reflections at the interferometer’s contacts caused by large interface potential barriers and effective mass mismatch between the contact material and the semiconductor. They are particularly strong in quasi-one-dimensional structures which, in fact, are preferred for spin interferometers because of the energy independence of the spin precession …

Generation–Recombination Noise In Gallium Nitride-Based Quantum Well Structures, Rolando S. Duran, Grover L. Larkins Jr., Carolyn M. Van Vliet, Hadis Morkoç

Electrical and Computer Engineering Publications

Electronic noise has been investigated in AlxGa1−xN/GaN modulation-doped field-effect transistors of submicron dimensions, grown by molecular beam epitaxy techniques. Some 20 devices were grown on a sapphire substrate. Conduction takes place in the quasi-two-dimensional (2D) layer of the junction (xy plane) which is perpendicular to the triangular quantum well (z direction). A nondoped intrinsic buffer layer separates the Si-doped donors in the AlxGa1−xN layer from the 2D transistor plane. Since all contacts must reach through the AlxGa1−xN layer to connect internally to the 2D plane, parallel conduction through this layer is a feature of all modulation-doped devices. The …

Infrared Optical Absorbance Of Intersubband Transitions In Gan/Algan Multiple Quantum Well Structures, Qiaoying Zhou, Jiayu Chen, B. Pattada, M. O. Manasreh, Faxian Xiu, Steve Putigan, K. S. Ramaiah, Hadis Morkoç

Electrical and Computer Engineering Publications

Intersubband transitions in Si-doped molecular beam epitaxygrown GaN/AlGaN multiple quantum wells on c-plane sapphire were investigated using the Fourier-transform infrared optical absorption technique. Several GaN quantum well samples were grown with either AlGaN bulk or GaN/AlGaN short period superlattice barriers. The measurements were made in a waveguide configuration utilizing a facet polished at 45° to the c plane. The integrated area of the intersubband transitions in several waveguides cut from different location of the wafer was measured, from which we estimated the two-dimensional electron gas density (σ). The measured values of σ are about two orders of magnitude larger …

Unusual Luminescence Lines In Gan, M. A. Reshchikov, D. Huang, F. Yun, P. Visconti, L. He, H. Morkoç, J. Jasinski, Z. Liliental-Weber, R. J. Molnar, S. S. Park, K. Y. Lee

Electrical and Computer Engineering Publications

A series of sharp intense peaks was observed in the low-temperature photoluminescence spectrum of unintentionally doped GaN in the photon energy range between 3.0 and 3.46 eV. We attributed the majority of these peaks to excitons bound to unidentified structural and surface defects. Most of the structural- and surface-related peaks (at 3.21, 3.32, 3.34, 3.35, 3.38, and 3.42 eV) were observed in Ga polar films. In N polar GaN, we often observed the 3.45 eV peak attributed to excitons bound to the inversion domain interfaces.

Contactless Electroreflectance, In The Range Of 20 K < T < 300 K, Of Freestanding Wurtzite Gan Prepared By Hydride-Vapor-Phase Epitaxy, Y. S. Huang, Fred H. Pollak, S. S. Park, K. Y. Lee, H. Morkoç

Electrical and Computer Engineering Publications

We have performed a detailed contactless electroreflectance study of the interband excitonic transitions on both the Ga and N faces of a 200-μm-thick freestanding hydride-vapor-phase-epitaxy grown wurtzite GaN sample with low defect concentration in the temperature range between 20 and 300 K. The transition energies of the A, B, and C excitons and broadening parameters of the A and B excitons have been determined by least-square fits to the first derivative of a Lorentzian line shape. The energy positions and separations of the excitonic transitions in the sample reveal the existence of residual strain. At 20 K the broadening parameter …

From Learning To Talk To Learning Engineering; Drawing Connections Across The Disciplines, Nikos J. Mourtos

Faculty Publications

This paper introduces eight so-called conditions of learning (immersion, demonstration, engagement, expectations, responsibility, approximation, employment and response), which have been previously established for the learning of literacy. It is stipulated that these conditions are universal in nature; in other words, they must be present for any learning to occur. When these conditions are met, students learn more efficiently and are able to enjoy and appreciate their subject matter. The article discusses briefly how these conditions were established and their relevance in the study of engineering. More importantly, the article also presents examples of how these conditions can be satisfied in …

Mass Transfer Coefficients For Laminar Longitudinal Flow In Hollow-Fibre Contactors, Ashok S. Sangani, Sangkyun Koo

Biomedical and Chemical Engineering - All Scholarship

We consider the problem of predicting the rate of mass transfer to a fluid flowing parallel to the axes of randomly placed aligned tubes, a model of hollow-fibre contactors. The analysis is carried out for the limiting cases of short contactors, for which the concentration boundary layers remain thin compared with the radius of the tubes, and for the fully developed case corresponding to very long tubes. Numerical simulations for random arrays are carried out for N randomly placed tubes within a unit cell of a periodic array. It is shown that the mass transfer coefficient for the fully developed …

Process Design, Development, Fabrication And Verification Of A Cmos Technology For Rit, Jeremiah L. Hebding

Journal of the Microelectronic Engineering Conference

The motivation in creation of the Strongarm process flow was to create a robust “enabling” process that was easy to manufacture. Optimum process conditions have been determined through extensive SUPREM simulation. Electrical examination using ATLAS software allowed for parameter extraction of the computer-generated devices. Modeling the extracted parameters with standard device physics equations allowed for a SPICE level-2 analysis that could be verified through electrical testing of actual fabricated devices. The technology was designed for a two micron, twin-well process incorporating a 4Onm gate oxide and an N+ poly gate. Source and drain implants are at 2E15 cm², …

Moving Rit To Submicron Technology: Fabrication Of 0.5Μm P-Channel Mos Transistors, Lisa M. Camp

Journal of the Microelectronic Engineering Conference

In this investigation, efforts have been made to move the Microelectronic Engineering Program at Rochester Institute of Technology to the next technology node by developing and fabricating a 0.5μm PMOS process. Currently, RIT is fabricating 1.0μm CMOS devices. A successful 0.5μm PMOS process can be incorporated into a full flow 0.5μm CMOS process. Both process and electrical simulations were done in order to predict performance. Key process features include blanket n-well, LOCOS isolation, 15nm gate oxide, i-line lithography, self-aligned source and drain, P+ doped polysilicon gates, and shallow source and drains. A test chip was created and the fabrication process …

Spice Parameter Extraction From Simulations And Experimental Data, Robert L. Saxer Jr

Journal of the Microelectronic Engineering Conference

SPICE parameters are a valuable tool used in the designing of integrated circuits. SPICE parameters communicate device behavior to circuit simulators. The purchase and support of Silvaco’s UTMOST software provided the function of extracting SPICE parameters from devices at RIT. With this new capability, RIT can obtain new levels of circuit simulation accuracy before fabrication. A method of SPICE parameter extraction was created and documented for simulated and experimental data.

Design And Fabrication Of Finfets On Soi Substrates, Steven D. Kirby

Journal of the Microelectronic Engineering Conference

A Fin Field Effect Transistor (FinFET) is one of several novel devices that may be used in the future to minimize short channel effects. The FinFET is fabricated on silicon on insulator (SOI) substrate and uses basic integrated circuit processing techniques to obtain a double gate structure. The double gate structure helps to improve subthreshold characteristics and provides low leakage current. The objective of this project was to improve the FinFET device built at RIT. Functioning FinFETs were designed and fabricated previously at RIT. The new design and process changes will help in the understanding of issues found in previous …

On The Influence Of Surface Treatment On Electrical Characteristics Of Schottky Diodes, Donald J. Hamilton

Journal of the Microelectronic Engineering Conference

The effect of surface treatment on electrical characteristics of aluminum-silicon contacts has been observed. It has been shown that the electrical characteristics of the contacts are affected by the quality of the interfacial oxide and sintering conditions. Four different surface treatments were performed on the silicon prior to metal deposition to vary the thickness and quality of the interfacial oxide. Four different sintering conditions were performed on the wafers to determine the effect of temperature and ramp-down rates. Three methods of calculating barrier height were used: current-voltage, current-temperature, and capacitance-voltage. Some results correlated well with previous reported work, however other …

Design, Simulation And Fabrication Of Insulated Gate Bipolar Transistors (Igbt), Tejas K. Jhaveri

Journal of the Microelectronic Engineering Conference

This project serves as a study to determine the feasibility of the current CMOS toolsets and processes available at Semiconductor & Microsystems Fabrication Laboratory (SMFL) for the fabrication of whole wafer power devices. Several designs and devices were explored. The Insulated Gate Bipolar Transistor (~LGBT) is a device widely used for high power electronic applications and was selected for this study. This device has bipolar current flow and a MOS gate thus combining advantages of both the Double diffused MOS (DMOS) and Power Bipolar junction transistor. Prototypes consisting of transistors with varying densities, gate lengths and gate widths were fabricated …

Optically Injected Circuits In A 0.18 Μm Cmos, Gregory Ardault

Journal of the Microelectronic Engineering Conference

Power consumption and power conversion efficiency have been two key parameters characterizing the performance of electronic circuits since their dawn. With the increasing demand of miniaturization, mobility and portability of electronic industrial and consumer equipment, low-power and high-efficiency circuits are in high demand. Possible energy sources to enable mobility and/or portability are chemical (e.g. batteries, accumulators, micro gas, engine, fuel cells), mechanical (e.g. elastic energy in springs, vibrations, oscillations, ultrasound), thermal (e.g. body heat), EM-Field (e.g. inductive coupling, capacitive coupling, RF) and optical (photovoltaic cells). They are a great number of applications for which lowpower operation can be replaced with …

Design And Testing Of Off Axis Illumination Filters For A 248nm Duv Exposure System, Matthew E. Malloy

Journal of the Microelectronic Engineering Conference

This study involves the design and testing of off axis illumination apertures for an ASML 5500/90 248nm DUV stepper. X and V slot pole apertures based on dipole theory were designed, fabricated out of aluminum, and inserted into the optical column of the stepper. Test patterns consisting of vertically oriented features were printed with and without dipole illumination, exposed, and compared to determine their effectiveness. As expected, features which were to small to print under standard illumination imaged exceptionally well using the x slot pole aperture. The y slot pole aperture delivered the same results as standard illumination which was …