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2012

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Articles 3301 - 3330 of 6306

Full-Text Articles in Engineering

Accurate Modeling Of Stability And Control Properties For Fighter Aircraft From Cfd, Jedediah H. Butler Mar 2012

Accurate Modeling Of Stability And Control Properties For Fighter Aircraft From Cfd, Jedediah H. Butler

Theses and Dissertations

Difficulties in obtaining accurate Stability and Control (S&C) data for nonlinear regions in the flight envelope early in the design phase often lead to costly fixes late in the acquisition process. Work examined herein addresses this problem by utilizing recent advances in Computational Fluid Dynamics (CFD) to create a high-fidelity database before any parts have to be physically produced. In combination with CFD, System Identification (SID) is used to characterize the S&C characteristics of aircraft by some Reduced Order Model (ROM). The method of obtaining enough data in the right places, via some optimized maneuver, to create an accurate ROM …

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Determination Of Effective Crossover Location And Dimensions For Branched Detonation In A Pulsed Detonation Engine, Louis A. Camardo Ii Mar 2012

Determination Of Effective Crossover Location And Dimensions For Branched Detonation In A Pulsed Detonation Engine, Louis A. Camardo Ii

Theses and Dissertations

A study is presented of the optimal crossover duct location and width to obtain consistent branched detonation transition from one detonation tube to another. On a Pulsed Detonation Engine (PDE) with detonation branching, the duct location at which the detonation crosses from one (primary) tube to a branched (secondary) tube impacts the number of successful detonations. In this paper, a comparison is made of the effects of the location and width of the crossover duct for hydrogen, ethylene and an n-alkane. The crossover location is varied from the aft end of the detonation tube to the middle of the detonation …

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Hybrid Solution Of Stochastic Optimal Control Problems Using Gauss Pseudospectral Method And Generalized Polynomial Chaos Algorithms, Gerald C. Cottrill Mar 2012

Hybrid Solution Of Stochastic Optimal Control Problems Using Gauss Pseudospectral Method And Generalized Polynomial Chaos Algorithms, Gerald C. Cottrill

Theses and Dissertations

Two numerical methods, Gauss Pseudospectral Method and Generalized Polynomial Chaos Algorithm, were combined to form a hybrid algorithm for solving nonlinear optimal control and optimal path planning problems with uncertain parameters. The algorithm was applied to two concept demonstration problems: a nonlinear optimal control problem with multiplicative uncertain elements and a mission planning problem sponsored by USSTRATCOM. The mission planning scenario was constructed to find the path that minimizes the probability of being killed by lethal threats whose locations are uncertain to statistically quantify the effects those uncertainties have on the flight path solution, and to use the statistical properties …

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Conceptual Layout Of Wing Structure Using Topology Optimization For Morphing Micro Air Vehicles In A Perching Maneuver, James R. Elgersma Mar 2012

Conceptual Layout Of Wing Structure Using Topology Optimization For Morphing Micro Air Vehicles In A Perching Maneuver, James R. Elgersma

Theses and Dissertations

A topology optimization model for conceptual wing structure layouts of morphing micro air vehicles (MAVs) has been developed and implemented in MATLAB. Specifically, a six degree-of-freedom finite element (FE) model with a general quadrilateral discretization scheme was created by superposition of a known simple linear plane membrane element and a Kirchhoff plate bending element derived herein. The purpose of the six degree-offreedom model was to accommodate in-plane and out-of-plane aerodynamic loading combinations. The FE model was validated and the MATLAB implementation was verified with classical beam and plate solutions. A compliance minimization optimization objective was then formulated with the Solid …

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Build Up And Operation Of An Axial Turbine Driven By A Rotary Detonation Engine, Jonathan R. Tellefsen Mar 2012

Build Up And Operation Of An Axial Turbine Driven By A Rotary Detonation Engine, Jonathan R. Tellefsen

Theses and Dissertations

Detonation combustors provide advantages over current deflagration combustors due to their pressure gain and simplicity of design. Rotary detonation engines (RDEs) offer advantages over pulsed detonation engines (PDEs) due to a steadier exhaust and fewer total system losses. All previous research on turbine integration with detonation combustors has focused on utilizing PDEs to drive axial and centrifugal turbines. The objective of this thesis was the integration and testing of an axial turbine driven by a rotary detonation engine (RDE) to determine turbine operability. In pursuit of this objective, convergent nozzle sections were placed on the RDE to simulate the back-pressurization …

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Empirical Analysis Of Optical Attenuator Performance In Quantum Key Distribution Systems Using A Particle Model, Thomas C. Adams Mar 2012

Empirical Analysis Of Optical Attenuator Performance In Quantum Key Distribution Systems Using A Particle Model, Thomas C. Adams

Theses and Dissertations

Quantum key distribution networks currently represent an active area of development and software modeling to address the security of future communications. One of the components used in quantum key distribution implementations is an optical attenuator. Its role in the system is necessary to reach the single photon per bit necessary to maintain theoretically perfect secrecy. How the photon pulse is modeled has a significant impact on the accuracy and performance of quantum channel components like the optical attenuator. Classical physics describe light using Maxwell's wave equations for electromagnetism. Quantum physics has demonstrated light also behaves as discrete particles referred to …

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Optimum Concentration Ratio Analysis Using Dynamic Thermal Model For Concentrated Photovoltaic System, John T. Avrett Mar 2012

Optimum Concentration Ratio Analysis Using Dynamic Thermal Model For Concentrated Photovoltaic System, John T. Avrett

Theses and Dissertations

Concentrated photovoltaic (PV) technology represents a growing market in the field of terrestrial solar energy production. As the demand for renewable energy technologies increases, further importance is placed upon the modeling, design, and simulation of these systems. Given the U.S. Air Force cultural shift towards energy awareness and conservation, several concentrated PV systems have been installed on Air Force installations across the country. However, there has been a dearth of research within the Air Force devoted to understanding these systems in order to possibly improve the existing technologies. This research presents a new model for a simple concentrated PV system. …

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Reynolds Number Effects On Thrust Coefficients And Piv For Flapping Wing Micro Air Vehicles, John P. Tekell Mar 2012

Reynolds Number Effects On Thrust Coefficients And Piv For Flapping Wing Micro Air Vehicles, John P. Tekell

Theses and Dissertations

For the last several years the Air Force Institute of Technology (AFIT) has conducted research in aerodynamics for flapping wing micro air vehicles (MAVs). The focus of this research was to augment this effort by measuring thrust, velocity, and torque in tanks of water and glycerin using a scale and a reaction torque cell. The results for different flapping mechanisms are compared to a rotating propeller with the goal of elucidating the design trade space between rotorcraft and flapping wings at Reynolds numbers less than 100,000. In addition, flow visualization and quantitative velocity data were captured in the wake of …

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Spectral Detection Of Human Skin In Vis-Swir Hyperspectral Imagery Without Radiometric Calibration, Andrew P. Beisley Mar 2012

Spectral Detection Of Human Skin In Vis-Swir Hyperspectral Imagery Without Radiometric Calibration, Andrew P. Beisley

Theses and Dissertations

Many spectral detection algorithms require precise ground truth measurements that are hand-selected in the image to apply radiometric calibration, converting image pixels into estimated reflectance vectors. That process is impractical for mobile, real-time hyperspectral target detection systems, which cannot empirically derive a pixel-to-reflectance relationship from objects in the image. Implementing automatic target recognition on high-speed snapshot hyperspectral cameras requires the ability to spectrally detect targets without performing radiometric calibration. This thesis demonstrates human skin detection on hyperspectral data collected at a high frame rate without using calibration panels, even as the illumination in the scene changes. Compared to an established …

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Integration Of Cold Atom Interferometry Ins With Other Sensors, Aaron J. Canciani Mar 2012

Integration Of Cold Atom Interferometry Ins With Other Sensors, Aaron J. Canciani

Theses and Dissertations

Inertial navigation systems (INS) using cold-atom interferometry are currently under development, and sensors in these systems are expected to be several orders of magnitude more ccurate than current navigation grade sensors. This signi cant increase in accuracy motivates the need to explore how these high accuracy inertial navigation systems can be integrated with other sensors. This research focuses on methods of integrating cold atom interferometry INS with conventional navigation grade INS, as well as with GPS. Results from a full 6 degree of freedom simulation show that integrating CAI INS with navigation grade INS is a successful way to address …

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Low Frequency Material Characterization Of Thin Substrates In A Coaxial Transmission Line, Lee B. Cole Mar 2012

Low Frequency Material Characterization Of Thin Substrates In A Coaxial Transmission Line, Lee B. Cole

Theses and Dissertations

This research analyzes the complex permittivity and permeability of thin material samples at low frequencies in the presence of large outer air gaps. It uses the modal method developed in previous research to account for the errors introduced to the system by the presence of higher order modes excited by the air gaps. The theoretical scattering parameters returned by the modal method are compared to the measured scattering parameters and the difference between the two is minimized using a complex root search algorithm. The method is tested with samples of a dielectric material and the magnetic material WaveX which respectively …

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Improving Knowledge Of C-130 Aircraft Condition: A High Velocity Maintenance Case Study, Marcus R. Mcwilliams Mar 2012

Improving Knowledge Of C-130 Aircraft Condition: A High Velocity Maintenance Case Study, Marcus R. Mcwilliams

Theses and Dissertations

High Velocity Maintenance (HVM) seems poised to revolutionize the way the Air Force schedules and performs depot-level maintenance on its aircraft. The four tenets of HVM -- Known Condition of the Aircraft, Supportability, Daily Standard Work, and High Burn Rate -- provide the basis for the Air Force's Air Logistics Centers (ALCs) to improve the quality of planning and scheduling that goes into each aircraft's depot maintenance visit. These tenets have been implemented at Warner Robins ALC as part of the C-130 depot maintenance process. While HVM is in active implementation there, much remains to be documented on how the …

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Aircraft Course Optimization Tool Using Gpops Matlab Code, Ryan D. Gauntt Mar 2012

Aircraft Course Optimization Tool Using Gpops Matlab Code, Ryan D. Gauntt

Theses and Dissertations

Aircraft course planning between two points in a clear, no threat environment is easy and straightforward. However, the addition of various threats can greatly increase the difficulty and complexity of course planning. Placing new waypoints along the edge of each threat, mostly skirting the dangerous environment, may not prove too difficult, but such courses are far from optimal. Given aircraft, environment, and time constraints it is likely a much more optimal path exists between any given start and end points. This research focuses on determining the feasibility of using the General Pseudospectral Optimization Software program files written for the MATLAB …

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Simplified Daylight Spectrum Approximation By Blending Two Light Emitting Diode Sources, Jacob M. Gilman Mar 2012

Simplified Daylight Spectrum Approximation By Blending Two Light Emitting Diode Sources, Jacob M. Gilman

Theses and Dissertations

Energy-conscious facility designs strive to include natural daylight in workspaces. To improve the efficiency of illumination, significant efforts are underway to adopt more efficient light emitting diode (LED) lamps and to effectively integrate daylight with active dimming of electric lighting. However, the correlated color temperature (CCT) and spectral content of daylight varies throughout the day while existing electric light sources produce light with a fixed CCT, resulting in mixed-illumination environments. The color rendering requirements for a lamp that permits the selection of color temperature across a significant portion of the daylight locus is explored. The analysis indicates that it is …

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Impact Of Self-Reported Biases And Familiarity In A Baggage Screening Context, Scott W. Halwes Mar 2012

Impact Of Self-Reported Biases And Familiarity In A Baggage Screening Context, Scott W. Halwes

Theses and Dissertations

A common assumption is that items that evoke strong emotions are more easily recognized than items that do not evoke strong emotions (Bessette-Symons, 2008). For example, items such as guns or knives may evoke strong emotions within some people, and it may be presumed that these items may be more easily recognized by people that have strong emotions associated with them. If this is true, then perhaps these people would be more apt to locate these items in situations such as baggage screening services that rely on accurate detection of weapons for the public's safety. This study explores this reasoning …

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Improving Effectiveness Of Monetary Weapon Systems In Afghanistan, Seth M. Lorimer Mar 2012

Improving Effectiveness Of Monetary Weapon Systems In Afghanistan, Seth M. Lorimer

Theses and Dissertations

Tenuous political and economic times call for increased oversight and improved results from military counterinsurgency programs in Afghanistan, programs that provide agile non-kinetic weapons, critical for commanders fighting in today's asymmetric battle space. This paper proposes a decision tool for construction projects executed under the Commanders Emergency Response Program, designed to meet the changing demands of fighting an amorphous insurgency among dynamic systems of stakeholders. The research first conducted a system analysis of the CERP project execution process identifying key findings addressing value adding inputs. The research then applies a Causal Chain, borrowed from the Emergency Management field to identify …

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Time-Valued-Technology: A Light-Emitting Diode Case Study For Determining Replacement Strategy For High Technology Infrastructure Items, Kevin S. Ochs Mar 2012

Time-Valued-Technology: A Light-Emitting Diode Case Study For Determining Replacement Strategy For High Technology Infrastructure Items, Kevin S. Ochs

Theses and Dissertations

Infrastructure projects have typically involved long-term investments in relatively mature technologies characterized by stable performance and cost. However, with the ever-increasing rate of technological innovation, an increasing number of potential infrastructure investments involve a decision to replace a traditional technology with a rapidly evolving technology. In such circumstances, it is possible to reap significant performance or cost advantages through near-term replacement. However, this rapid adoption strategy has the potential to incur an opportunity cost due to increased performance or cost advantages the technology would provide if replacement was delayed. This research develops a cost analysis method, referred to as time-valued-technology, …

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Stabilizing Acetylcholinesterase On Carbon Electrodes Using Peptide Nanotubes To Produce Effective Biosensors, Todd J. Stevens Mar 2012

Stabilizing Acetylcholinesterase On Carbon Electrodes Using Peptide Nanotubes To Produce Effective Biosensors, Todd J. Stevens

Theses and Dissertations

A biosensor for the detection of organophosphates in water was created by immobilizing acetylcholinesterase (AChE) on a carbon screen printed electrode using peptide nanotubes (PNT) and Nafion®. This sensor was used with acetylthiocholine (ASCh) substrate to detect the inhibitory effects of malathion. The stability of the encapsulated enzyme was measured over 50 days of storage at 4°C in a phosphate buffer solution. The oxidation of thiocholine, a product of the enzymatic reaction of ASCh and AChE, was used to measure the activity of the encapsulated enzyme. Cyclic voltammograms were taken in an ASCh and phosphate buffer solution, and the peak …

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Magnetic Field Generation And B-Dot Sensor Characterization In The High Frequency Band, Ryan L. Hardin Mar 2012

Magnetic Field Generation And B-Dot Sensor Characterization In The High Frequency Band, Ryan L. Hardin

Theses and Dissertations

Designing a high frequency (HF) magnetic field direction finding (DF) array for use onboard a military aircraft is the challenge that drives the effort of the research presented. The frequency range of interest, 2-32 MHz, has a maximum wavelength (150 meters) that exceeds the maximum length of any platform in the USAF inventory. The large wavelengths in the HF range make it difficult to accurately estimate from which direction a magnetic field is emitting. Accurate DF estimates are necessary for search and rescue operations and geolocating RF emitters of interest. The primary goal of this research is to characterize the …

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Design, Modeling, And Measurement Of A Metamaterial Electromagnetic Field Concentrator, Noel A. Humber Mar 2012

Design, Modeling, And Measurement Of A Metamaterial Electromagnetic Field Concentrator, Noel A. Humber

Theses and Dissertations

This document addresses the need to improve the design process for creating an optimized metamaterial. In particular, two challenges are addressed: creating an electromagnetic concentrator and optimizing the design of metamaterial used to create the electromagnetic concentrator. The first challenge is addressed by developing an electromagnetic field concentrator from a design of concentric geometric shapes. The material forming the concentrator is derived from the application of transformation optics. The resulting anisotropic, spatially variant constitutive parameter tensors are then approximated with metamatieral inclusions using the combination of an AFIT rapid metamaterial design process and a design process created for rapid metamaterial …

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Improvements To Optical Communication Capabilities Achieved Through The Optical Injection Of Semiconductor Lasers, Timothy P. Locke Mar 2012

Improvements To Optical Communication Capabilities Achieved Through The Optical Injection Of Semiconductor Lasers, Timothy P. Locke

Theses and Dissertations

Optically injection locked lasers have shown significant improvement in the modulation capabilities of directly modulated lasers. This research creates a direct-modulated optical communications system to investigate the bit-rate distance improvements achievable using optically injected Fabry-Pérot laser diodes. The injection strength and detuning frequency of the injection signal was varied to determine their impact on the optical communication link's characteristics. This research measured a 25 fold increase in bit-rate distance product using optical injection locking as compared to the injected laser's free-running capability. A 57 fold increase was measured in the bit-rate distance product when signal power is considered in a …

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Computer Aided Multi-Data Fusion Dismount Modeling, Juan L. Morales Mar 2012

Computer Aided Multi-Data Fusion Dismount Modeling, Juan L. Morales

Theses and Dissertations

Recent research efforts strive to address the growing need for dismount surveillance, dismount tracking and characterization. Current work in this area utilizes hyperspectral and multispectral imaging systems to exploit spectral properties in order to detect areas of exposed skin and clothing characteristics. Because of the large bandwidth and high resolution, hyperspectral imaging systems pose great ability to characterize and detect dismounts. A multi-data dismount modeling system where the development and manipulation of dismount models is a necessity. This thesis demonstrates a computer aided multi-data fused dismount model, which facilitates studies of dismount detection, characterization and identification. The system is created …

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Near Earth Object Detection Using A Poisson Statistical Model For Detection On Images Modeled From The Panoramic Survey Telescope And Rapid Response System, Curtis J. R. Peterson Mar 2012

Near Earth Object Detection Using A Poisson Statistical Model For Detection On Images Modeled From The Panoramic Survey Telescope And Rapid Response System, Curtis J. R. Peterson

Theses and Dissertations

The purpose of this research effort is to develop, simulate, and test a new algorithm to detect Near Earth Objects (NEOs) using a Likelihood Ratio Test (LRT) based on a Poisson statistical model for the arrival of photons. One detection algorithm currently in use is based on a Gaussian approximation of the arrival of photons, and is compared to the proposed Poisson model. The research includes three key components. The first is a quantitative analysis of the performance of both algorithms. The second is a system model for simulating detection statistics. The last component is a collection of measured data …

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All Source Sensor Integration Using An Extended Kalman Filter, Timothy R. Penn Mar 2012

All Source Sensor Integration Using An Extended Kalman Filter, Timothy R. Penn

Theses and Dissertations

The global positioning system (GPS) has become an ubiquitous source for navigation in the modern age, especially since the removal of selective availability at the beginning of this century. The utility of the GPS is unmatched, however GPS is not available in all environments. Heavy reliance on GPS for navigation makes the warfighter increasingly vulnerability as modern warfare continues to evolve. This research provides a method for incorporating measurements from a massive variety of sensors to mitigate GPS dependence. The result is the integration of sensor sets that encompass those examined in recent literature as well as some custom navigation …

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Covariance Analysis Of Vision Aided Navigation By Bootstrapping, Andrew L. Relyea Mar 2012

Covariance Analysis Of Vision Aided Navigation By Bootstrapping, Andrew L. Relyea

Theses and Dissertations

Inertial Navigation System (INS) aiding using bearing measurements taken over time of stationary ground features is investigated. A cross country flight, in two and three dimensional space, is considered, as well as a vertical drop in three dimensional space. The objective is to quantify the temporal development of the uncertainty in the navigation states of an aircraft INS which is aided by taking bearing measurements of ground objects which have been geolocated using ownship position. It is shown that during wings level flight at constant speed and a fixed altitude, an aircraft that tracks ground objects and over time sequentially …

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Using Vft As A Constraint For Goal Programming Models: A Case Study For Turkish Air Force Flying Hour Program, Ahmet Bengoz Mar 2012

Using Vft As A Constraint For Goal Programming Models: A Case Study For Turkish Air Force Flying Hour Program, Ahmet Bengoz

Theses and Dissertations

In its 60-year history, there have been many published documents in the literature about goal programming (GP), but contributions to the literature are still needed. This research intends to add to the literature on goal-programming models by discussing one of the key assumptions of GP regarding linearity, and by discussing some of the issues regarding incommensurability (difference in data types) and weighting. GP requires an interaction between the decision maker (DM) and the analyst to ensure that the model reflects the DM's preferences. However, it may be difficult for them to interact if the mathematical model is very large and …

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Investigation And Synthesis Of Novel Graphene-Based Nanocomposites For Hydrogen Storage, Anthony Joseph D'Angelo Mar 2012

Investigation And Synthesis Of Novel Graphene-Based Nanocomposites For Hydrogen Storage, Anthony Joseph D'Angelo

USF Tampa Graduate Theses and Dissertations

It is of great interest to develop and utilize a high surface area material with optimized hydrogen sorption properties. The need for a renewable energy source to replace automobile gasoline has become more critical in the past decade. Hydrogen is a viable fuel source for automobile usage; however, the question of how hydrogen will be safely and efficiently stored still remains. Critical factors for optimum hydrogen storage include ambient conditions and low activation temperature for adsorption and desorption phenomena. In order for optimum hydrogen adsorption to be achieved, the properties of (1) high surface area, (2) optimum hydrogen adsorption energy, …

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Combustion Simulations Using Graphic Processing Units, Mingjie Wang Mar 2012

Combustion Simulations Using Graphic Processing Units, Mingjie Wang

Master's Theses

Graphic processing units (GPUs) are powerful graphics engines featuring high levels of parallelism and extreme memory bandwidth, which constitute a powerful computing platform to solve complex problems involving chemically reacting flows. In the present study, computer programs for combustion simulations with detailed chemical kinetic mechanisms were compiled in the Compute Unified Device Architecture (CUDA) language for NVIDIA GPU architecture. Ignition processes were simulated under constant pressure and constant volume conditions using an explicit 4th order Runge-Kutta algorithm for time integration. Sufficiently small time steps were identified with time scale analysis to ensure the integration stability. The program was validated …

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Sr2Fe1.5Mo0.5O6-Δ – Sm0.2Ce0.8O1.9 Composite Anodes For Intermediate-Temperature Solid Oxide Fuel Cells, Beibei He, Ling Zhao, Shuxiang Song, Tong Liu, Fanglin Chen, Changrong Xia Mar 2012

Sr2Fe1.5Mo0.5O6-Δ – Sm0.2Ce0.8O1.9 Composite Anodes For Intermediate-Temperature Solid Oxide Fuel Cells, Beibei He, Ling Zhao, Shuxiang Song, Tong Liu, Fanglin Chen, Changrong Xia

Faculty Publications

Sr2Fe1.5Mo0.5O6−δ (SFM) perovskite is carefully investigated as an anode material for solid oxide fuel cells with LaGaO3-based electrolytes. Its electronic conductivity under anodic atmosphere is measured with four-probe method while its ionic conductivity is determined with oxygen permeation measurement. Samaria doped ceria (SDC) is incorporated into SFM electrode to improve the anodic performance. A strong relation is observed between SDC addition and polarization losses, suggesting that the internal SFM-SDC contacts are active for H2 oxidation. The best electrode performance is achieved for the composite with 30 wt% SDC addition, resulting …

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A Ceramic-Anode Supported Low Temperature Solid Oxide Fuel Cell, Hanping Ding, Junjie Ge, Xingjian Xue Mar 2012

A Ceramic-Anode Supported Low Temperature Solid Oxide Fuel Cell, Hanping Ding, Junjie Ge, Xingjian Xue

Faculty Publications

We report the fabrication and evaluation of a ceramic-anode supported button cell LSCM-SDC/SDC/PBSC (thickness 400 μm/20 μm/20 μm). The anode/electrolyte assembly LSCM-SDC/SDC was co-fired at low temperature of 1250°C, where a slight amount of CuO was mixed with LSCM. The CuO (20.3 wt%) were impregnated into the porous substrate to enhance current collecting effect. The cell exhibited power density of 596 mWcm−2 and 381 mWcm−2 at 700°C with wet hydrogen and methane as the fuel respectively, where the silver paste was used as current collectors, the highest performance up to date for the cells with metal oxide anodes at this …

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