Engineering Commons^™

Simulated Performances Of A Heat Pump System For Energy And Water Conservation In Open And Confined Greenhouse Systems, Ilhami Yildiz, D. P. Stombaugh

BioResource and Agricultural Engineering

The purpose of this study was to determine and compare the performances of conventional and heat pump systems for energy and water conservation in open and confined greenhouse systems. Conventional gas furnaces and evaporative cooling, respectively, provided heating and cooling in the conventional system. In the heat pump systems, gas-fired heat pump units provided both heating and cooling. The greenhouse with heat pump units also had an option to be operated as a completely confined system, using one of the heat pump units as a dehumidifier. Average energy consumption in winter was 56.9, 23.5, and 11.3 MJ/day.m² in the conventional, …

Aerothermodynamic Cycle Analysis Of A Dual-Spool, Separate-Exhaust Turbofan Engine With An Interstage Turbine Burner, Ka Heng Liew

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

This study focuses on a specific engine, i.e., a dual-spool, separate-flow turbofan engine with an Interstage Turbine Burner (ITB). This conventional turbofan engine has been modified to include a secondary isobaric burner, i.e., ITB, in a transition duct between the high-pressure turbine and the low-pressure turbine. The preliminary design phase for this modified engine starts with the aerothermodynamics cycle analysis is consisting of parametric (i.e., on-design) and performance (i.e., off-design) cycle analyses.

In parametric analysis, the modified engine performance parameters are evaluated and compared with baseline engine in terms of design limitation (maximum turbine inlet temperature), flight conditions (such as …

Flight Physician - January, 2006, Civil Aviation Medical Association

Browse all Civil Aviation Medical Association Newsletters

A twenty page newsletter of the Civil Aviation Medical Association. The newsletter provided news about civil aviation medicine and information related to the organization.

Hybrid Solar Cells From Water-Soluble Polymers, James T. Mcleskey Jr., Qiquan Qiao

Mechanical and Nuclear Engineering Publications

We report on the use of a water-soluble, light-absorbing polythiophene polymer to fabricate novel photovoltaic devices. The polymer is a water-soluble thiophene known as sodium poly[2-(3-thienyl)-ethoxy-4-butylsulfonate] or PTEBS. The intention is to take advantage of the properties of conjugated polymers (flexible, tunable, and easy to process) and incorporate the additional benefits of water solubility (easily controlled evaporation rates and environmentally friendly). The PTEBS polythiophene has shown significant photovoltaic response and has been found to be effective for making solar cells. To date, solar cells in three different configurations have been produced: titanium dioxide (TiO2) bilayer cells, TiO2 bulk heterojunction solar …

Comparison Of The Pull-Out Strengths Of Three Different Screws In Pedicular Screw Revisions: A Biomechanical Study, Irfan Esenkaya, Yurdaer Denizhan, Mehmet Akif Kaygusuz, Mehmet Yetmez, Mehmet Halidun Keleştemur

Faculty Publications - Mechanical Engineering

OBJECTIVES: We investigated the possible effects of three pedicular screws on axial pull-out strength in pedicular revision surgery. METHODS: Two study groups were formed from calf lumbar vertebrae. Initially, Alici pedicular screws with an outer diameter of 6.5 mm were applied (with or without tapping) to all the pedicles. All the pedicles were subjected to axial pull-out testing to induce pedicular insufficiency. Then, Alici pedicular screws with an outer diameter of 7 mm were applied to the left pedicles. The right pedicles in the two study groups were assigned to receive two different types of pedicular screws with an expandable …

Amplification Of Streamflow Impacts Of El Niño By Increased Atmospheric Greenhouse Gases, Edwin P. Maurer, Seran Gibbard, Philip B. Duffy

Civil, Environmental and Sustainable Engineering

Some El Niño events produce unusually large precipitation amounts in Northern and Central California. We use a high-resolution global model of the atmosphere coupled to a physically-based model of surface hydrology to investigate effects of increased atmospheric CO2 and this type of El Niño, both individually and in combination, on monthly river flows in California. Increased CO2 changes the seasonal timing of river flows and increases their variability. SST anomalies typical of a strong El Niño SST increase monthly-mean flows. The two perturbations together result in increased mean flows and increased variability, raising the possibility of both increased flood risk …

Multiple Lebesgue Integration On Time Scales, Gusein Sh. Guseinov, Martin Bohner

Mathematics and Statistics Faculty Research & Creative Works

We study the process of multiple Lebesgue integration on time scales. The relationship of the Riemann and the Lebesgue multiple integrals is investigated.

Optimal Management Of Groundwater Over Space And Time, Nicholas Brozovic, David L. Sunding, David Zilberman

Daugherty Water for Food Global Institute: Faculty Publications

For nearly half a century, groundwater has been portrayed in the economic literature as a typical common property resource. Numerous studies of groundwater extraction have analyzed the externalities imposed by users on each other. A large body of work offers clear prescriptions in the form of optimal policy instruments, and a similarly large body of work advocates the needlessness of any centralized intervention. Yet existing theoretical models of groundwater extraction implicitly make two strong assumptions about the underlying behavior of the resource. First, the spatial distribution of resource users is assumed to be irrelevant. Second, path-independence of the resource is …

Acuta Enews January 2006, Vol.35, No. 1

ACUTA Newsletters

In This lssue

From ACUTA Headquarters Jeri A. Semer, CAE, ACUTA Executive Director

ACUTA Audio Seminar: Creative Cost Savings in Communications Technology

Tech Talk: Skype May be Unwanted, But at Least lt's Not Harmful............ Kevin Tanzillo, Dux PR

Institutional Excellence Award Deadline

FYI: Useful lnformation from the Campus................ Student Monitor

Web Tip: Online Directory and Other Useful Resources. Aaron Fuehrer, ACUTA lnformation Tech. Mgr.

Thanks to Sponsors for 2005

Board Report................. Riny Ledgerwood, San Diego State Univ., ACUTA Sec./Treasurer

DC Update.................. Whitney Johnson, Retired, No. Michigan Univ.

Welcome New Members

ACUTA Online Press Room

The Utep Corpus Of Iraqi Arabic, Nigel Ward, David G. Novick, Salamah I. Salamah

Departmental Technical Reports (CS)

The rules governing turn-taking phenomena are not well understood in general and almost completely undocumented for Arabic. As the first step to modeling these phenomena, we have collected a small corpus of Iraqi Arabic spoken dialogs. The corpus is in three parts. Part A is 110 minutes of unstructured conversations. Parts B1 and B2 are 176 minutes of direction-giving dialogs, most including a greeting phase, a smalltalk phase, a request phase, and a direction-giving phase. Parts A and B1 were recorded with 13 native speakers of Iraqi Arabic, interacting in pairs. In Part B2 the direction-getter is an American with …

Defect Reduction In (112¯0) A-Plane Gan By Two-Stage Epitaxial Lateral Overgrowth, X. Ni, Ü. Özgür, Y. Fu, N. Biyikli, J. Xie, A. A. Baski, Hadis Morkoç, Z. Liliental-Weber

Electrical and Computer Engineering Publications

The authors report a two-stage epitaxial lateral overgrowth (ELO) method to get uniformly coalesced (112¯0) a-plane GaN using metal organic chemical vapor deposition by employing a relatively lower growth temperature in the first stage followed by conditions leading to enhanced lateral growth in the second. Using a two-stage ELO method the average Ga-polar to N-polar wing growth rate ratio has been reduced from 4–6 to 1.5–2, which consequently reduced the height difference between the two approaching wings at the coalescence front that resulted from the wing tilt (0.44° for Ga and 0.37° for N wings, measured by x-ray diffraction), thereby …

Band Offset Measurements Of Zno∕6h-Sic Heterostructure System, Ya. I. Alivov, Bo Xiao, Q. Fan, Hadis Morkoç, D. Johnstone

Electrical and Computer Engineering Publications

The conduction band offset of n-ZnO∕n-6H-SiCheterostructures fabricated by rf-sputtered ZnO on commercial n-type 6H-SiC substrates has been measured by a variety of methods. Temperature dependent current-voltage characteristic, photocapacitance, and deep level transient spectroscopy measurements showed the conduction band offsets to be 1.25, 1.1, and 1.22eV, respectively.

Near-Field Scanning Optical Microscopy And Time-Resolved Optical Characterization Of Epitaxial Lateral Overgrown C-Plane And A-Plane Gan, Ü. Özgür, X. Ni, Y. Fu, Hadis Morkoç, H. O. Everitt

Electrical and Computer Engineering Publications

Epitaxial lateral overgrowth (ELO) was employed for both c-plane and a-plane GaN layers on sapphire, and a more pronounced optical improvement was observed for the a-plane GaN as evidenced by the significantly increased band edge photoluminescence(PL). Room temperature near-field scanning optical microscopy studies explicitly showed enhanced optical quality in the wing regions of the overgrown GaN due to reduced density of dislocations, and for the a-plane ELOGaN sample the wings and the windows were clearly discernible from PL mapping. Time-resolved PLmeasurements revealed biexponential decays with time constants that were significantly enhanced for the a-plane ELOGaN (τ1=0.08ns, τ2=0.25ns) when compared to …

Comparative Study Of The (0001) And (0001) Surfaces Of Zno, S. A. Chevtchenko, J. C. Moore, Ü. Özgür, Xing Gu, A. A. Baski, Hadis Morkoç, B. Nemeth, J. E. Nause

Electrical and Computer Engineering Publications

The authors compare the surface and optical properties of the Zn-polar (0001) and O-polar (0001¯)surfaces of bulk ZnO samples. For optical characterization, steady-state photoluminescence using a He–Cd laser was measured at 15 and 300K. At room temperature, the (0001¯)surface demonstrates nearly double the near-band-edge emission intensity seen for the (0001) surface. Using scanning Kelvin probe microscopy, the authors have measured surface contact potentials of 0.39±0.05 and 0.50±0.05V for the (0001) and (0001¯)surfaces, respectively. The resulting small difference in band bending for these two surfaces indicates that charge transfer between the surfaces is not a dominant stabilizing mechanism. Conductive atomic force …

I-V Characteristics Of Au∕Ni Schottky Diodes On Gan With Sinx Nanonetwork, J. Xie, Yi Fu, Xianfeng Ni, S. A. Chevtchenko, Hadis Morkoç

Electrical and Computer Engineering Publications

Room temperature and temperature dependent current-voltage characteristics of Ni∕AuSchottky diodes fabricated on undoped GaN prepared with and without in situ SiNxnanonetwork by metal organic chemical vapor deposition have been studied. The features of the Schottky diodes depend strongly on the SiNx deposition conditions, namely, its thickness. Reduction in the point and line defect densities caused the Schottky barrier height to increase to1.13eV for 5min SiNx deposition time as compared to 0.78eV without SiNx nanonetwork. Similarly, the breakdown voltage also improved from 76V for the reference to 250V when SiNx nanonetwork was used. With optimized SiNx nanonetwork, full width at half …

Near-Infrared Wavelength Intersubband Transitions In Gan∕Aln Short Period Superlattices, E. D. Decuir Jr., Emil Fred, B. S. Passmore, A. Muddasani, M. O. Manasreh, Jinqiao Xie, Hadis Morkoç, M. E. Ware, G. J. Salamo

Electrical and Computer Engineering Publications

Intersubband transitions in GaN∕AlN short period superlattices prepared by molecular beam epitaxy were investigated using the optical absorption technique. The peak position wavelengths of these transitions are found to span the spectral range of 1.35–2.90μm for samples cut into 45° waveguides with GaNquantum well thicknesses ranging between 1.70 and2.41nm. The Fermi energy levels are estimated from the carrier concentrations, which were measured using an electrochemical capacitance-voltage profiler. The well widths were inferred from comparing the measured peak position energy of the intersubband transitions and the bound state energy levels calculated using the transfer matrix method.

Observation Of Numerous E2 Mode Phonon Replicas In The Room Temperature Photoluminescence Spectra Of Zno Nanowires: Evidence Of Strong Deformation Potential Electron-Phonon Coupling, S. Ramanathan, S. Bandyopadhyay, L. K. Hussey, M. Muñoz

Electrical and Computer Engineering Publications

The authors report the observation of numerous (>20)phonon replica peaks in the room temperature photoluminescence spectrum of ZnOnanowires embedded in 50nm diameter pores of an anodic alumina film. The peaks are spaced in energy by ∼54meV, which is the energy of a nonpolar phonon with symmetry E2 in ZnO. These peaks are possibly caused by resonant phonon-assisted decay of photoexcited electrons to an impurity band, followed by radiative recombination. These results suggest that even though ZnO is strongly polar, deformation potential coupling to a nonpolar phonon mode may be stronger than Fröhlich coupling to polar phonon modes.

High Quality Epitaxial Growth Of Pbtio3 By Molecular Beam Epitaxy Using H2o2 As The Oxygen Source, Xing Gu, Natalia Izyumskaya, Vitaliy Avrutin, Hadis Morkoç, Tae Dong Kang, Hosun Lee

Electrical and Computer Engineering Publications

Single crystalline PbTiO3films have been epitaxially grown on SrTiO3 (001) substrates by molecular beam epitaxy using H2O2 as the source of active oxygen. The optimum growth conditions have been determined by analyzing a range of growth parameters affecting growth and used to attain single phase and stoichiometric PbTiO3thin films.In situ reflection high-energy electron diffraction pattern indicated the PbTiO3films to be grown under a two-dimensional growth mode. The full width at half maximum of the rocking curve of a relatively thin65nm (001) PbTiO3film is 6.2arcmin which is indicative of high crystal quality. The band gap of PbTiO3, as determined by …

Subpicosecond Time-Resolved Raman Studies Of Lo Phonons In Gan: Dependence On Photoexcited Carrier Density, K. T. Tsen, Juliann G. Kiang, D. K. Ferry, Hadis Morkoç

Electrical and Computer Engineering Publications

Subpicosecond time-resolved Raman spectroscopy has been used to measure the lifetime of the LO phonon mode in GaN for photoexcited electron-hole pair density ranging from1016to2×1019cm−3 . The lifetime has been found to decrease from 2.5ps , at low density, to0.35ps , at the highest density. The experimental findings should help resolve the recent controversy over the lifetime of LO phonon mode in GaN.

Infrared Absorption In A Quantum Wire: A Technique To Measure Different Types Of Spin-Orbit Interaction Strengths, S. Bandyopadhyay, S. Sarkar

Electrical and Computer Engineering Publications

We show that the dominant absorption peak due to intersubband transition in a gated quantum wire will split into a main peak and two satellite peaks if both Rashba and Dresselhaus spin-orbit interactions are present. One satellite peak will be redshifted, and the other blueshifted. From the relative intensity of either satellite peak, and the magnitude of the red- or blueshift, we can determine both Rashba and Dresselhaus interaction strengths separately, if we also carry out a Hall measurement to determine the carrier concentration and a quantized conductance step measurement to determine the energy separation between subbands. This method …

Quantitative Mobility Spectrum Analysis Of Algan∕Gan Heterostructures Using Variable-Field Hall Measurements, N. Biyikli, J. Xie, Y.-T. Moon, F. Yun, C.-G. Stefanita, S. Bandyopadhyay, Hadis Morkoç, I. Vurgaftman

Electrical and Computer Engineering Publications

Carrier transport properties of AlGaN∕GaNheterostructures have been analyzed with the quantitative mobility spectrum analysis (QMSA) technique. The nominally undoped Al0.08Ga0.92N∕GaN sample was grown by plasma-assisted molecular beam epitaxy on a GaN/sapphire template prepared with hydride vapor phase epitaxy. Variable-magnetic-field Hall measurements were carried out in the temperature range of 5–300K and magnetic field range of 0.01–7T. QMSA was applied to the experimental variable-field data to extract the concentrations and mobilities associated with the high-mobility two-dimensional electron gas and the relatively low-mobility bulk electrons for the temperature range investigated. The mobilities at T=80K are found to be 7100 and 880cm2/Vs, respectively, …

In Situ Pendeoepitaxy Of Gan Using Heteroepitaxial Algan∕Gan Cracks, Y. T. Moon, C. Liu, J. Xie, X. Ni, Y. Fu, Hadis Morkoç, Lin Zhou, David J. Smith

Electrical and Computer Engineering Publications

Pendeoepitaxy on patterned templates has been proven to be efficient for reducing threading dislocation densities in GaN thin films. In this letter, we report on in situ crack-assisted pendeoepitaxy of GaN using spontaneously formed cracks in AlGaN∕GaNheterostructures. Our approach involves the growth of an AlGaN∕GaNtemplate followed by in situ thermal etching and deposition of an amorphous silicon nitride mask in a low pressure metal organic chemical vapor deposition system. Microwirelike GaN seeds are then formed along the crack lines during the initial stage of GaN overgrowth, which act as nucleation stripes for epitaxial lateral overgrowth. Transmission electron microscopy revealed that …

Fabrication And Current-Voltage Characterization Of A Ferroelectric Lead Zirconate Titanate/Algan∕Gan Field Effect Transistor, Youn-Seon Kang, Qian Fan, Bo Xiao, Ya. I. Alivov, Jinqiao Xie, Norio Onojima, Sang-Jun Cho, Yong-Tae Moon, Hosun Lee, D. Johnstone, Hadis Morkoç, Young-Soo Park

Electrical and Computer Engineering Publications

We demonstrated ferroelectricfield effect transistors (FFETs) with hysteretic I-V characteristics in a modulation-doped field effect transistors(MODFET)AlGaN∕GaN platform with ferroelectricPb(Zr,Ti)O3 between a GaN channel and a gate metal. The pinch-off voltage was about 6–7V comparable to that of conventional Schottky gate MODFET. Counterclockwise hysteresis appeared in the transfer characteristics with a drain current shift of ∼5mA for zero gate-to-source voltage. This direction is opposite and much more pronounced than the defect induced clockwise hysteresis in conventional devices, which suggests that the key factor contributing to the counterclockwise hysteresis of the FFET is the ferroelectric switching effect of the lead zirconate titanate …

Effect Of Hydrostatic Pressure On The Dc Characteristics Of Algan∕Gan Heterojunction Field Effect Transistors, Y. Liu, P. P. Ruden, J. Xie, Hadis Morkoç, K.-A. Son

Electrical and Computer Engineering Publications

We report the effect of compressive hydrostatic pressure on the current-voltage characteristics ofAlGaN∕GaNheterojunction field effect transistors (HFETs) on a sapphire substrate. The drain current increases with hydrostatic pressure and the maximum relative increase occurs when the gate bias is near threshold and drain bias is slightly larger than saturation bias. The increase of the drain current is associated with a pressure induced shift of the threshold voltage by −8.0mV∕kbar that is attributed to an increase of the polarizationcharge density at the AlGaN∕GaN interface due to the piezoelectric effect. The results demonstrate the considerable potential of AlGaN∕GaNHFETs for strain sensor applications.

Effect Of C∕Si Ratio On Deep Levels In Epitaxial 4h–Sic, C. W. Litton, D. Johnstone, S. Akarca-Biyikli, K. S. Ramaiah, I. Bhat, T. P. Chow, J. K. Kim, E. F. Schubert

Electrical and Computer Engineering Publications

Changing the ratio of carbon to silicon during the epitaxial 4H–SiC growth is expected to alter the dominant deep level trap, which has been attributed to a native defect. The C∕Si ratio was changed from one to six during epitaxialgrowth of SiC. Diodes fabricated on the epitaxial layer were then characterized using current-voltage and deep level transient spectroscopy. The single peak at 340K (Z1/Z2 peak), was deconvolved into two traps, closely spaced in energy. The concentration of one of the Z1/Z2 traps decreased with increasing C∕Si ratio. This result opposes theoretical predictions of carboninterstitial components, and supports assignment to a …

Admittance Of Cds Nanowires Embedded In Porous Alumina Template, A. Varfolomeev, D. Zaretsky, V. Pokalyakin, S. Tereshin, S. Pramanik, S. Bandyopadhyay

Electrical and Computer Engineering Publications

CdSnanowires of 10nm diameter, electrodeposited in porous alumina films, had shown a conductance bistability in the past [Appl. Phys. Lett.76, 460 (2000)]. The conductance has a high (ON) and a low (OFF) state. In the ON state, different sets of nanowires display qualitatively different relation between the conductance and capacitance. We propose a model to explain this anomalous behavior. Based on this model, we predict that the inelastic mean free path of electrons in the nanowires is 3–3.5nm at room temperature. This short mean free path may be a consequence of acoustic phonon confinement.

Gallium Desorption Kinetics On (0001) Gan Surface During The Growth Of Gan By Molecular-Beam Epitaxy, L. He, Y.-T. Moon, J. Xie, M. Muñoz, D. Johnstone, Hadis Morkoç

Electrical and Computer Engineering Publications

Gallium (Ga) surfacedesorption behavior was investigated using reflection high-energy electron diffraction during the GaNgrowth. It was found that the desorption of Ga atoms from the (0001) GaNsurfaces under different III-V ratio dependents on the coverage of adsorbed atoms. Doing so led to desorption energies of 2.76 eV for Ga droplets, 1.24–1.89 eV for Ga under Ga-rich growth conditions, and 0.82 eV – 0.94 eV for Ga under stoichiometric growth conditions. Moreover, the variation of the GaNsurface morphology under different III-V ratios on porous templates supports the conclusion that Ga desorption energy depends on the coverage, and the III/V ratio dominates …

Spin Relaxation Of “Upstream” Electrons In Quantum Wires: Failure Of The Drift Diffusion Model, Sandipan Pramanik, Supriyo Bandyopadhyay, Marc Cahay

Electrical and Computer Engineering Publications

The classical drift diffusion (DD) model of spin transport treats spin relaxation via an empirical parameter known as the “spin diffusion length.” According to this model, the ensemble averaged spin of electrons drifting and diffusing in a solid decays exponentially with distance due to spin dephasing interactions. The characteristic length scale associated with this decay is the spin diffusion length. The DD model also predicts that this length is different for “upstream” electrons traveling in a decelerating electric field than for “downstream” electrons traveling in an accelerating field. However, this picture ignores energy quantization in confined systems (e.g., quantum wires) …

Weak Antilocalization And Zero-Field Electron Spin Splitting In Alxga1−Xn∕Aln∕Gan Heterostructures With A Polarization-Induced Two-Dimensional Electron Gas, Ç Kurdak, N. Biyikli, Ü. Özgür, Hadis Morkoç, V. I. Litvinov

Electrical and Computer Engineering Publications

Spin-orbit coupling is studied using the quantum interference corrections to conductance in AlxGa1−xN∕AlN∕GaN two-dimensional electron systems where the carrier density is controlled by the persistent photoconductivity effect. All the samples studied exhibit a weak antilocalization feature with a spin-orbit field of around 1.8mT. The zero-field electron spin splitting energies extracted from the weak antilocalization measurements are found to scale linearly with the Fermi wave vector (ESS=2αkf) with an effective linear spin-orbit coupling parameter α=5.5×10−13eVm. The spin-orbit times extracted from our measurements varied from 0.74 to 8.24pswithin the carrier density range of this experiment.

Dislocation Reduction In Gan Grown On Porous Tin Networks By Metal-Organic Vapor-Phase Epitaxy, Y. Fu, F. Yun, Y. T. Moon, Ü. Özgür, J. Q. Xie, X. F. Ni, N. Biyikli, H. Morkoç, Lin Zhou, David J. Smith, C. K. Inoki, T. S. Kuan

Electrical and Computer Engineering Publications

We report on the effectiveness of porous TiN nanonetworks on the reduction of threading dislocations (TDs) in GaN grown by metal-organic vapor-phase epitaxy (MOVPE). The porous TiN networks were formed by in situ annealing of thin-deposited Ti films deposited ex situ on GaN templates within the MOVPE growth chamber. Different annealing parameters in relation to surface porosity of TiN networks were investigated. Transmission electron micrographs indicated dislocation reduction by factors of up to 10 in GaN layers grown on the TiN nanonetwork, compared with a control sample. TiN prevented many dislocations present in the GaN templates from penetrating into the …