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2004-2005 Aerospace Graduate Research Fellows and
Aerospace Undergraduate Research Scholars
Abstracts and Research Papers (.pdf)
Presented at the Student Research Conference - April 1, 2005
Omni Hotel, Newport News, Virginia


Aerospace Graduate Research Fellows

The Construction and Assembly of Cryostat Exit Detectors for Backward Angles of the GO Experiment
Stephanie Bailey, The College of William and Mary

The goal of experiment E00-006 (the G0 experiment), currently underway at the Thomas Jefferson
National Accelerator Facility is to investigate the contributions of the strange quarks to the fundamental properties of the nucleon. This will be achieved by measuring parity-violating scattering asymmetries off the proton at both forward and backward angles. In the most basic picture, the G0 experiment is comprised of a beam of polarized electrons from the Jefferson Lab accelerator, a liquid hydrogen target, and a Focal Plane Detector (FPD) made up of scintillators. The backward angle experiment requires a new set of scintillator detectors, Cryostat Exit Detectors (CEDs). The objective of my research this past year was to assist in the construction and assembly of the CEDs.

Spatial Habitat Detection of Mosquitoes Using Remote-Sensing Techniques and a GIS
Alan Scott Bellows, Old Dominion University

My primary objective is to create a predictive, spatially explicit classification model capable of identifying, categorizing, and ranking suitable mosquito habitat in heterogeneous landscapes with an emphasis on those mosquito species known to be vectors of West Nile Virus. Lifehistory processes dictate organismal distributions, and these distributions are often a function of spatial land cover patterns (i.e., land cover composition and configuration). Thus, I hypothesized that local mosquito abundance could be predicted from a parsimonious set of measurable landscape factors. Thematic layers digitally representing landscape factors in the model’s first iteration include: land-cover, soil characteristics, wetland classification, and vegetation characteristics. Spatial composition and configuration of vegetation are closely linked with species diversity and abundance. The vegetation indices (VI) used here (i.e., Normalized Difference Vegetation Index [NDVI], Tasseled Cap transformation) are useful tools for inferring photosynthetic activity and vegetative structure. Results of these VIs were derived via direct interpretation of Landsat ETM+ imagery by incorporating mathematical operations between and among spectral bands. Collectively, these layers will be used to statistically elucidate relationships between mosquito abundance landscape factors. These relationships will in turn, be used to rank habitat suitability. The integration of digital satellite remote sensing and GIS technologies with applied ecology and epidemiology will produce an effective and cost efficient model for remotely locating, and subsequently controlling, mosquitoes across large areas.

Electromechanical Transducers Based on Nafion / Ionic Liquid Composites
Matt Bennett, Virginia Tech

Ionic liquids have shown promise as replacements for water in ionic polymer transducers. Ionic liquids are non-volatile and have a larger electrochemical stability window than water. Therefore, transducers employing ionic liquids can be operated for long periods of time in air and can be actuated with higher voltages. However, the physics of transduction in the ionic liquid-swollen materials is not well understood. In this paper, the morphology of Nafion / ionic liquid composites is compared to the electromechanical transduction behavior. The results reveal that both the morphology and transduction performance of the composites is affected by the identity of the ionic liquid, the cation, and the amount of ionic liquid within the membrane. Specifically, speed of response is found to be lower for the membranes that were exchanged with smaller ions. The response speed is also found to increase with increased content of ionic liquid. Furthermore, for the two ionic liquids studied, the actuators swollen with the less viscous ionic liquid exhibited a slower response. The slower speed of response corresponds to less contrast between the ionically conductive phase and the inert phase of the polymer. This suggests that disruption of the clustered morphology in the ionic liquid-swollen membranes attenuates ion mobility within the polymer. This attenuation is attributed to swelling of the non-conductive phase by the ionic liquids.

Standards-based P2P Communications Systems
David Bryan, The College of William and Mary

Current Voice over IP (VoIP) and Instant Messaging (IM) systems follow a client-server model, or require clients and network elements supporting non-standard protocols. In this paper, we present a standards-based, fully decentralized peer-to-peer (P2P) communications system. This system can be used in situations where constant Internet connectivity is not possible, and supports ad hoc, ephemeral communications scenarios. These systems are useful in environments including remote locations, security conscious organizations, and collaborative groups. Our system leverages the existing SIP/SIMPLE family of open-standard protocols, ensuring that our system will interoperate with existing communications infrastructure. We implement our system using a Distributed Hash Table (DHT) approach for lookup, transported using SIP messages. We support replication for reliability and availability. Our system uses unmodified SIP/SIMPLE mechanisms to exchange messages after resources are located, allowing for maximal reuse. We explore future directions of research for such systems, including security, availability, and advanced routing, including social-based routing techniques.

Cultural Differences in Situation Awareness, Shared Mental Model, & Workload Perceptions in American & Chinese Simulated Flightcrews
Janet Bryant, Old Dominion University

Human error is responsible for most aircraft accidents. Many of these errors can be traced to ineffective team behaviors and processes in the cockpit. Crew resource management (CRM) seeks to redress poor flightcrew performance by training pilots and copilots to work effectively as a team. While CRM has been effective in the US in reducing the number of aircraft accidents, it may not be generalizable to other cultures. Specifically, values of other cultures may conflict with CRM ideology, which is steeped in Western values. This study examined the influence of national culture on three measures of task activity—situational awareness, shared mental model, and workload perceptions—in 149 simulated flightcrews. Chinese and American male graduate and undergraduate students were divided into homogeneous (i.e., same culture Chinese or same culture American) and heterogeneous (i.e., Chinese and American) teams. Results show significant differences in situational awareness and workload perceptions among the three experimental conditions. However, there were no significant differences in shared mental model across the three team types. Measures of cultural values failed to explain differences situational awareness, shared mental model, and workload perceptions. Limitations of the current research design are discussed, along with directions for future study of cultural influences on teamwork.

Infrared Laser Absorption Tomography
Elliott Bryner, University of Virginia

In the design of air-breathing engines computational and analytical tools are often used in the early stages of the design process to reduce testing and prototyping. The Aerospace Research Laboratory at The University of Virginia is involved in a project to validate computational fluid dynamics calculations for use in design of dual-mode scramjet engines. One important parameter used in optimizing performance of scramjets is combustion efficiency. To determine the combustion efficiency of a model scramjet I am developing a technique to measure water vapor concentration produced in the combustor. In a hydrogen fueled scramjet the combustion efficiency can be calculated by measuring the amount water vapor and finding it’s the ratio to the amount of fuel supplied. The concentration of water vapor leaving the combustor is to be measured by a technique called infrared laser absorption tomography. Infrared laser absorption tomography combines two measurement techniques; infrared laser absorption spectroscopy and tomographic image reconstruction. Tomography, or image reconstruction from projections is the technique used in medical CT scans and produces a spatially resolved two-dimensional distribution of the measurement space. Infrared laser absorption spectroscopy is used to measure species concentration and temperature in many combustion flow applications and will be combined with tomographic imaging and implemented at the supersonic combustion tunnel at The University of Virginia’s Aerospace Research Laboratory (ARL).

Application of Quaternion Algebra - Inertial Navigation and Guidance
(Powerpoint presentation for Application of Quaternion Algebra - Inertial Navigation and Guidance)
George P. Davailus, Old Dominion University

Currently, many six degree of freedom (6-DOF) trajectory simulations and simulations of gyroscopic motion use quaternions to define a vehicle’s orientation. Of those that do, however, none take full advantage of the properties of quaternion algebra. Quaternions are also known as hypercomplex numbers. They can be treated as individual quantities for which all the standard algebraic operations are defined. Consequently, they have advantages that Euler angles and transformation matrices do not. This paper will describe the use of quaternion algebra and elliptic functions to obtain a closed form solution for torque free gyroscopic motion in terms of the rotational quaternion and its derivative. It will also define an alternative 6-DOF formulation, that, when combined with quaternion algebra, is potentially much more powerful than current simulations.

Measurements of Internal and External Heat Transfer for Turbine Blade Applications
Erin Elder, Virginia Tech

Efficiency and power output of gas turbines improve with an increase in turbine rotor inlet temperatures. Innovative cooling methods are used by blade designers to raise turbine inlet temperatures to levels higher than the melting temperatures of the blade material. These increased turbine inlet temperatures are achieved by utilizing a combination of internal convective cooling and external film cooling. Internal convective cooling, flowing air through the internal passages of the blade, is further augmented by pin fin arrays. These pin fins serve to turbulate the air thereby augmenting convective cooling. The coolant flow exits internal cooling passages to the external side of the blade and forms a protective layer along the external surface of the blade further cooling the blade. In the current study, a novel low-speed large-scale wind tunnel facility was developed with the capability to measure both internal heat transfer coefficients, using thermal liquid crystal, and external adiabatic effectiveness, using an infrared camera. Friction factor values, the limiting factor in cooling designs, were also measured. The test facility has been used to characterize several proprietary cooling configurations, and is currently in use for the testing of public pin fin designs.

The Absolute Space Motions of Galactic Clusters
Peter Frinchaboy, University of Virginia

NASA's Space Interferometry Mission (SIM) is a satellite-based optical interferometer that will measure the positions of and distances to a strategically chosen set of stars with several scientific goals in mind, including the measurement of the mass of the Milky Way galaxy. The SIM project has chosen Galactic clusters as the best tracer of the mass distribution of the Milky Way disk. We are conducting a project to provide SIM targets, using precision radial velocities to verify cluster membership for stars in Galactic clusters. As a result of this open cluster survey, we have found that the outer most open clusters have different properties from most clusters. With further investigation, we have found that these outer, old open clusters seem to lie in an orbital plane concurrent with a newly found stellar tidal stream, and may not be part of Galactic disk. We present the first results of the chemo-dynamics of these, possibly accreted, clusters which will allow us to determine two things: 1) what are the properties of this new galaxy's clusters system, and 2) what are the most distant open clusters that can be used reliably in the study of mass distribution in the Milky Way disk.

Characterization of InGaAs Linear Focal Plane Array for Applications to Remote Sensing
Christopher Garcia, Old Dominion University

An Indium Gallium Arsenide linear photodiode array in the 1.1-2.5 µm spectral range was characterized. The array has 1024X1 pixels with a 25 µm pitch and was manufactured by Sensors Unlimited, Inc. Characterization and analysis of the electrical and optical properties of a camera system were carried out at room temperature to obtain detector performance parameters. The signal and noise were measured while the array was uniformly illuminated at varying exposure levels. A photon transfer curve was generated by plotting noise as a function of average signal to obtain the camera gain constant. The spectral responsivity was also measured, and the quantum efficiency, read noise and full- well capacity were determined. This paper describes the characterization procedure, analyzes the experimental results, and discusses the applications of the InGaAs linear array to future earth and pla netary remote sensing mission.

Phase-Field Computer Model of Microstructure Evolution in a Ferromagnetic Shape Memory Alloy
Todd Heil, Virginia Tech

The phase-field method has been successfully employed during the past ten years to simulate a wide variety of microstructural evolution in materials. Phase-field models describe the microstructure of a material by using a set of field variables whose evolution is governed by thermodynamic functionals and kinetic continuum equations. A phasefield model to describe martensitic and magnetic domain features in ferromagnetic shape memory alloys is presented. The purpose of this model is to serve as a predictive tool to guide ferromagnetic shape memory alloy design. Free energy functionals are based on the phase-field microelasticity and micromagnetic theories; they account for energy contributions from composition, temperature, martensite variant boundaries, elastic strain, applied stress, magnetocrystalline anisotropy, magnetic domain walls, magnetostatic potential, and applied magnetic fields. The time-dependent Ginzburg-Landau and Landau-Lifshitz kinetic continuum equations are employed to track the microstructural and magnetic responses in ferromagnetic shape memory alloys to applied temperature, stress, and/or magnetic fields. The model successfully predicts the expected microstructural responses to these applied fields.

Gradient Based Spectral Peak Location For Noise Robust Speech Recognition
Penny Hix, Old Dominion University

In this paper a gradient-based algorithm for finding spectral peak locations is presented. The algorithm makes use of gradient and acceleration locations in the spectrogram for locating the peaks. Use of frequency gradients and accelerations locate peaks. The results are then interpolated to yield a smooth peak envelope. The method is evaluated in the aurora framework. A first pass locates all spectral peaks and automatically eliminates low magnitude, high frequency peaks that are likely to contain more noise than speech information. The second pass widens the spectral peaks with spectral information. This widening is expected to increase automatic speech recognition based on the peak envelope discrete cosine transformation feature representation.

Functional Analysis of the MicroMAPS Instrument Performance During Flights Onboard the Proteus Aircraft
Patrick Hopkins, University of Virginia

The scientific goal of the Microprocessor-based Measurement of Air Pollution from Satellites (MicroMAPS) project is to measure Carbon Monoxide (CO) mixing ratios in the middle troposphere from an airborne platform. During June through September 2004, MicroMAPS flew aboard the Proteus aircraft over the southern California coast, the Atlantic Ocean, and the Mediterranean Sea. In order to continue with retrieval of data from these flights, the flight conditions and instrument functionality must be examined. An engineering assessment of the MicroMAPS instrument performance based on data collected from both laboratory tests and airborne flights is presented. Information from this analysis is used to calculate the averaging kernel for the Proteus flight and MicroMAPS instrument conditions. The MicroMAPS averaging kernel is then applied to in situ data to produce simulated MicroMAPS total column CO mixing ratio data for flights over the Atlantic. Data retrieval calculations and methods are briefly discussed.

Development and Spectroscopic Characterizaiton of CR+2 Diffusion Doped ZnSe for Mid-Infrared Laser Applications
Ivy Jones, Hampton University

The preparation and optical spectroscopy of diffusion doped Cr:ZnSe and Cr:CdTe polycrystalline windows will be reported. Cr2+ doped II-VI semiconductors have recently emerged as a new class of room-temperature operated widely tunable (2-3 µm) midinfrared (MIR) solid-state lasers. The demonstration of efficient lasing from diffusion doped polycrystalline Cr:ZnSe windows provide an attractive method for producing MIR laser materials at low cost. For the advancement of current Cr2+ chalcogenide lasers, however, it is critical to gain a better understanding of the Cr2+ incorporation and infrared optical properties in II-VI host. In this work results of Cr diffusion experiments performed, will be presented on commercial ZnSe and CdTe windows. Compared to Cr:ZnSe, Cr:CdTe offers the advantage of an extended MIR emission with a larger emission cross-section beyond 3000nm. Cr doping was achieved in both window materials through a thermal diffusion process controlled by temperature (750-850°C) and time (0.25-6 days). Commercial CrSe powder (99.5% purity) was used as the dopant source. Various samples of Cr:ZnSe and Cr:CdTe were prepared with Cr2+ peak absorption coefficients ranging from ~1 cm-1 to 25 cm-1. The estimated Cr2+ concentrations ranged from ~5x1017cm-3 to ~3x1019cm-3 assuming absorption-cross sections of 1.1x10-18cm2 for Cr:ZnSe and 2.2x10-18cm2 for Cr:CdTe. For low Cr2+ concentrations (~1x1018cm-3) the room-temperature decay time varied between 5-6 µs for Cr:ZnSe and 2-3µs for Cr:CdTe. Based on low temperature (15K) lifetime data, the emission efficiencies were estimated to be ~75% for Cr:CdTe and ~95% for Cr:ZnSe. The effect of Cr concentration quenching on the MIR emission was observed for doping concentrations above ~1x1019cm3. A more detailed discussion of the absorption and MIR emission properties of Cr:ZnSe and Cr:CdTe windows as a function of Cr concentration will be presented at the conference.

Characterization of the Solvent-induced Nonlinear Response of Ionic Polymer Actuators
Curt Kothera, Virginia Tech

Ionic polymer transducers exhibit coupling between the electrical, chemical, and mechanical domains, allowing their use as both sensors and actuators. Because of their compliance, light weight, and low voltage operation, ionic polymers have received considerable attention, although their fundamental mechanisms are still open for debate. While most of the existing models provide linear, dynamic approximations of the response, nonlinear characteristics have been observed in the laboratory. Recent experimental results have shown that the solvent plays a significant role in the dynamic response of these actuators in the cantilever configuration. Given a single-frequency input voltage, the major difference from changing solvents was concluded to be a varying distortion, seen in both the actuation current and tip velocity measurements. This research looks to further explore this nonlinear distortion by incorporating a larger set of candidate solvent materials and investigating the impact of how changing properties affect the overall response. System identification techniques using the Volterra series are employed to aid in the characterization of the harmonic distortion. The knowledge gained in this study will provide useful information about the nature of the nonlinearity and some of the factors that affect its relative influence, which will assist physical model development.

Dual-Mode Scramjet Isolator Flow Studies
Daniel Le, University of Virginia

An experimental investigation of a dual-mode scramjet isolator is presented. A constant area isolator was fabricated and tested in conjunction with a Mach 2, hydrogenair combustor operating at a simulated Mach 5 flight enthalpy. Predicted isolator performance was validated through pressure measurements obtained via low frequency pressure taps. These measurements demonstrated that the maximum pressure ratio measured in the combustor approached the design, and normal shock, limit of 4.5. The measurements also indicated that scramjet operability was improved. Mode transition from supersonic to subsonic combustion, without isolator-inlet interaction, was achieved for an equivalence ratio (ö) range of 0.06-0.32, as opposed to 0.32-0.37 without the isolator. Shock train location repeatability was found to vary somewhat with ö. Timeresolved pressure fluctuations at steady-state ö were measured using high frequency pressure transducers in the isolator to estimate the level of shock train unsteadiness. The shock train was found to be relatively steady and the time-resolved measurements generally agreed with available low frequency pressure measurements to within one standard deviation. The time-resolved measurements were also obtained for rising and falling ö and these measurements indicated that large pressure fluctuations occurred near the leading edge of the shock train. These results suggest that shock train location and control may be achieved by monitoring the magnitude of such fluctuations. Other shock train leading edge detection methods were developed using 150% of the average pressure and pressure fluctuations upstream of the shock train. The results suggest that using 150% of the average pressure fluctuations upstream of the shock train provides the earliest indication of impending shock train leading edge. Power spectrum analyses were generated to study the relationship between dominant frequency components of the Fourier transform and the shock train leading edge.

CO2 Production in Water and Amorphous Carbon
Mark Loeffler, University of Virginia

Here we present laboratory studies where we measure, using infrared spectroscopy, the production of CO2 from amorphous carbon grains with a water ice cap that have been irradiated with 100 keV H+ ions. We find that CO2 is produced in both thin films where the ions hit the substrate and in thicker films where the ions stop in the ice film. Furthermore, we have found that we produce more CO2 at 16 K than we do at 120 K. Also after we desorb the water ice, we use infrared spectroscopy to detect semi-stable carbonaceous species left on the substrate. One of the species identified is carbonic acid, H2CO3, which shows that even with two of the most basic substances present in outer space, more complex molecules can be produced by radiation processing.

An Interference Temperature Model for Improving Spectrum Access
David Maldonado-Febus, Virginia Tech

In an effort to improve radio spectrum management and promote more efficient use of the spectrum, the Federal Communications Commission (FCC) is trying to adopt a new model to quantify interference. The objective of my research project is to develop an “Interference Temperature” (IT) model for this purpose. The IT model aims to create a reference interference level using real-time measurements and predictions based on the actual RF environment seen at a receiver. This resulting interference temperature would reflect the total amount of RF energy present at the receiver within the operating band at any given point in time. The transmitter would configure itself in response to this value. My presentation reviews some of the technical challenges involved in the implementation of such a model. It discusses several proposed approaches. The advantages, disadvantages and some possible applications for this metric will be investigated and analyzed. As an example, I discuss how the IT concept could be used in a proposed plan for frequency sharing plan between existing TV broadcast stations and new unlicensed services using Software Defined Cognitive Radios.

Splitter Vanes in Axial Flow Compressor Rotors
Jonathan McGlumphy, Virginia Tech

Splitter vanes are additional, smaller airfoils that are placed circumferentially between the main blades of a compressor rotor. They have been used for decades in centrifugal rotors, and have been shown to improve overall performance in terms of pressure ratio and efficiency. Wennerstrom (circa 1974) was the first to use the splitter concept in an axialflow rotor. His experiments indicated that in addition to the known benefits from centrifugal rotors, the splitters would also improve flow control in the axial flow when operating at off-design conditions. In spite of these potential benefits, there has been no known commercial application of the splittered axial rotor. The goal of this project is to determine if splitter vanes can be successfully utilized in a commercial gas turbine engine. If so, it would allow designers to use fewer stages in a compressor, thus reducing both manufacturing and operating costs of the engine. The first portion of the project will involve an extensive numerical study of various 2D geometries. Pertinent parameters include the shape and position of the splitter vane relative to the main rotor blades. 3D solvers will be used in the latter stages of the project.

Mobius, An Omni-Directional Robot Utilizing Mecanum Wheels and Fuzzy Logic Control
Sam Miller, Old Dominion University

This talk presents the results of a project to develop an omni-directional robotic system at NASA Langley’s Robotics and Intelligent Machines Lab. The robot, named Mobius, was created as part of an investigation into omni-directional motion (using four Mecanum wheels) and fuzzy-logic control. The robot uses a high-level processor running Linux to connect to wireless networks, process user-input data, relay camera imagery, and communicate with a low-level microcontroller. All the programs for user input and imagery viewing are cross-platform, Internet-enabled, client-server applications. When within range of a wide-area-network wireless access point, Mobius can be driven from an arbitrary location on the Internet. Low-level control of Mobius’ motors is through a simple microcontroller-based fuzzy-logic algorithm. The robot platform is capable of translation in any direction, bidirectional rotation, and simultaneous translation with rotation. Future work includes constructing a vehicle with three Mecanum wheels and autonomous algorithms. The algorithms will fuse sonar ranging with stereoscopic and panoramic imagery for autonomous robot navigation and topologic robot localization.

Design, Control, and Experimental Modeling of a Morphing Aircraft Configuration
David Neal, Virginia Tech

This work describes the design, control, and Phase One wind-tunnel testing of the XAPV, an experimental adaptive planform vehicle. The XAPV is an experimental testbed designed at Virginia Tech for aerodynamic modeling and flight control testing. The model is capable of large-scale planform changes for multi-mission flight as well as smooth contour changes for low-drag, high-authority maneuvering. The vehicle’s uniqueness is the combination of several ‘morphing’ control parameters on a single platform. The XAPV has independent control of wing span, sweep, twist, and horizontal stabilizer location. The tailboom also contains a flow-vectoring nozzle which provides independent yaw control. The vehicle is capable of respective increases in span and aspect ratio of 60 and 150 percent. The design layout and actuation system is described including trajectory control of the pneumatic actuators that drive the system. Experimental testing is conducted in Virginia Tech’s Stability Tunnel to identify static aerodynamic parameters. The aerodynamics are first modeled as quasi-steady functions of the configuration. This work is the first step towards developing a comprehensive model of the XAPV suitable for morphing flight control design.

Modeling and Control of Thin Strip Membranes
Eric Ruggiero, Virginia Tech

Ultra-lightweight, ultra-large and deployable satellite technology is at the forefront of research efforts for future on-orbit reconnaissance missions. The minimal mass and stowage volume associated with the technology are attractive traits for getting larger bandwidth satellites on-orbit. One of the key components for such a satellite is the membrane lens or aperture for optical or radar applications, and understanding the membrane’s dynamics is critical for mission success. As either an optical reflector or radar antenna, the vibration levels of the membrane must be minimized and eliminated. This work examines the possibility of integrating a PZT bimorph near the boundary of a strip sample to eliminate detrimental vibration. By starting with a 1-D model, the dominant governing phenomena of the system dynamics can be established and used to build more complex models with confidence. A physics-based finite element (FE) model of a thin strip of Kapton HN material with a monolithic PZT bimorph bonded near a boundary is developed in a MatLab environment and verified experimentally. The membrane strip under tension is modeled as a beam under axial load. In doing so, the FE model is able to capture the relevant transverse dynamics of the experimental setup. Having verified the FE model, an LQR controller is developed and simulated to demonstrate effective control over the transverse dynamics of the membrane sample. In addition, insight into the optimal placement of sensors is garnered through the careful mathematical development of the distributed parameter problem.

Mechanics of Multiwall Carbon Nanotubes
Aaron Sears, Virginia Tech

To realize the incredible structural applications potential of carbon nanotubes, it is important to characterize their material response. Molecular simulations offer advantages over physical testing due to their cost effectiveness, versatility and precision. Two continuum models for single wall nanotubes (SWNT) were previously developed based on the results from molecular simulations using two different potentials. The continuum models have been found to predict both global and local responses for buckling well. Radial expansion and contraction simulations of double wall nanotubes confirmed that the assumption of isotropy of a nanotube wall response is accurate. The SWNT continuum models were used as the basis to model multi-wall nanotubes (MWNT). In continuum mechanics, the equivalence to the van der Waals forces is pressure. Using the results from the expansion/contraction simulations the pressure between two walls was defined as a function of the wall separation. A continuum model for MWNTs was developed using finite element (FE) analysis with shell elements for the walls and truss elements to substitute for pressure. The predictions from the FE models are compared to molecular simulations. Preliminary work on nanotube/polymer composite material is also presented.

Ultrafast Pump-probe Experiments of Exchange Biased Bilayers
Keoki Seu, The College of William and Mary

We have excited and detected coherent spin waves in exchange-biased IrMn/Co systems by ultrafast laser pump-probe magneto-optical Kerr effect (MOKE). Such ultrafast measurements provide opportunity to study the ultimate time scale for these processes as well as determination of fundamental parameters such as anisotropy and damping. This is in analogy with ferromagnetic resonance (FMR), but with the benefit of direct access to the time domain, sub-micron spatial resolution and straightforward in-situ application. These exchange biased IrMn/Co systems are frequently used in magnetic sensors for disk based storage and magnetic random access memory devices (MRAM) for non-volatile storage. The coherent spin waves detected are single frequency, with a frequency which depends strongly on applied magnetic field. The spin waves exist in all orientations, applied fields, and exchange biased field strengths tested. The frequencies were fit to FMR theory using terms for the exchange biasing and demagnetization fields.

Deep Chandra & Hubble Observations of NGC 4697, the Nearest Optically Luminous, X-ray Faint Elliptical Galaxy
Gregory Sivakoff, University of Virginia

With NASA's Chandra X-ray Observatory, we have accumulated over two days of data from NGC 4697, the nearest optically luminous, X-ray faint elliptical galaxy. These observations provide one of the deepest views of low-mass X-ray binaries (LMXBs; binary stars, with one normal star with M.MSun and either a neutron star or black hole, which emit profuse amounts of X-rays) in an elliptical galaxy. In addition to detecting lower luminosity LMXBs, these observations allow us to probe the variability behavior of the brighter LMXBs. We derive the timescales over which LMXBs may be transient and discover aring behavior with no clear analog in our own Galaxy. With our Hubble Space Telescope observations, which reveal the population of globular clusters (GCs; dense, spherical concentrations of millions of stars), we _nd that approximately one-third of the LMXBs are in GCs and that approximately one-tenth of the GCs contain LMXBs. We explore various aspects of the LMXB-GC connection. These explorations, when combined with data from other galaxies, will allow us to answer questions about the formation and evolution of LMXBs, GCs, and elliptical galaxies.

Discovery of Nitrogen in Saturn's Inner Magnetosphere
H. Todd Smith, University of Virginia

We have discovered N+ in Saturn’s inner magnetosphere by using a combination of modeling and analysis of Cassini Plasma Science (CAPS) instrument data. The presence of N+ in Saturn’s magnetosphere has been a source of much debate since Voyager’s detection of unresolved mass/charge 14-16 amu ions in this region. Two principal nitrogen sources have been suggested: Titan’s atmosphere and nitrogen compounds trapped in Saturn’s icy satellite surfaces (Sittler et al 2004a, b). The latter may contain primordial nitrogen, likely as NH3 in ice (Stevenson 1982; Squyers et al. 1983) or N+ that has been implanted in the surface (Delitsky and Lane 2002). Here I present the initial nitrogen cloud modeling generated from Titan’s atmosphere as well as our detection of N+ in Saturn’s magnetosphere in the range L~3.5 to ~9.5 using data collected by the CAPS during Saturn Orbit Insertion and the following orbit (Rev A). In addition to our nitrogen detection results, I present an initial examination of possible sources of these ions. This work is supported by the Virginia Space Grant Consortium Graduate Research Fellowship, NASA Planetary Atmospheres, NASA Graduate Student Research, and CAPS Cassini instrument team programs.

Effect of Long Length Scale Roughness on Giant Magnetoresistive Films
Shannon Watson, The College of William and Mary

Increasing interfacial roughness effects giant magnetoresistance through enhanced interfacial and spin-dependent scattering, or through a change in magnetic coupling. Recent work has explored the effects of roughness on GMR and modeling has shown that such roughness may cause the GMR to increase or decrease depending on several parameters such as roughness amplitude, period and electron mean free path. Experimentally, an increase in GMR connected to increased scattering at the interfaces has been shown to be directly related to vertical and lateral roughness amplitude. However, in previous studies, the roughness was only varied through a change in sputtering parameters and produced lateral variations < 10 nm and rms roughness less than 5 nm. We are exploring roughness on a larger length scale (lateral period > 10 nm, rms amplitudes > 5 nm), introduced through the substrate. Our investigation shows that large scale interface roughness produces either a small increase in magnetoresistance or has little effect. These results are important for applications in which GMR multilayers are deposited on non-standard substrates and buffer layers, such as flexible media, where the roughness is greater than traditional materials.

Electromagnetic Propagation Prediction Inside Airport Terminals
Mennatoallah Youssef, Old Dominion University

Airport terminals across the globe will eventually be equipped with wireless networks to provide information access and services to passengers. However, airport terminals as well as airplanes are vulnerable to electromagnetic attack. Therefore, electromagnetic propagation models for signal strength prediction within airport terminals are essential for evaluating and designing wireless communication systems; it will also assess the effectiveness of radio frequency (RF) attack inside airport terminals. The focus of this effort is to evaluate the effectiveness of using commercial grade software - intended for electromagnetic predictions within office buildings- to develop models to analyze propagation inside airplane fuselages and airport terminals. The project goal is to verify that the Wireless XGTD and Insite software can accurately predict power propagation within airport terminals and airplane fuselages. Additionally, electromagnetic coupling between the interior and the exterior of an airport terminal, adjacent buildings and objects will be examined. Previous propagation models tested proved to be accurate predictors inside empty airplane fuselages. Current work uses fuselage models which containing additional internal components. The methodology used for airplanes will be extended to airport terminals. Results from airport terminals currently being examined are expected by the end of the semester.

Self-Sustained Acoustic Response of Counterflow Methane-Air Premixed Flames
Andrea Zambon, University of Virginia

Thermo-acoustic instabilities represent a major technical problem in many combustion applications and are generally manifested as large-amplitude pressure oscillations coupled with unsteadiness in the combustion processes. In the present analysis, the interaction of acoustic waves with planar counterflow methane-air premixed flames is investigated numerically for a range of flow strain rates and flame locations, and employing a detailed and one-step global finite-rate kinetic models. It is found that one-step global models with large activation energy always promote the amplification of acoustic pressure fluctuations in counter-flow premixed flames, whereas the detailed kinetic model exhibit thermo-acoustic instabilities for specific locations of the flame. While previous unsteady counterflow work required external perturbations, the resonant unsteady phenomena predicted in this study are self-sustained under favorable boundary conditions. A detailed analysis of the characteristic time-scales associated with convection, diffusion, chemistry and acoustics is accompanied by an analysis of the heat release rate and of the effects of flame location in order to provide a better understanding of the fundamental coupling mechanisms driving the instability, namely chemical kinetic-acoustic coupling and acoustically-induced fluctuations in the mass flux of reactants into the flame.

Monitoring Available Bandwidth of Underlying Grid Networks
Marcia Zangrilli, The College of William and Mary

Harnessing the complete power of grids depends, in part, on an application’s ability to adapt to changing network conditions. To this end, we are interested in monitoring available bandwidth of the underlying grid networks in the most accurate and least obtrusive way. Available bandwidth is either measured by actively injecting data probes into the network or by passively monitoring existing traffic, but there is a definite trade-off between the active approach, which is invasive, and the passive approach, which is rendered ineffective during periods of network idleness. Our solution is to develop the Wren bandwidth monitoring tool, which uses a hybrid approach to network monitoring that combines elements of passive and active techniques to offer accurate, timely available bandwidth measurements while limiting the invasiveness of probes. We have completed a packet trace facility, designed new passive bandwidth algorithms to measure the available bandwidth, and evaluated the effectiveness of these new algorithms in diverse environments. Our results indicate that a low overhead, passive monitoring system supplemented with active measurements can be built to obtain a complete picture of the network’s performance.

Aerospace Undergraduate Research Scholars

Characterization of Strain Rate Dependence in the Mechanical Behavior of Gold Thin Films
Colin P. Bateson, University of Virginia

The effect of strain rate on the mechanical behavior of gold thin-films for RF-MEMS applications was examined. Microscale, free-standing, dog bone shaped specimens were subjected to uniaxial tension tests at strain rates ranging between 10-6 s-1 and 10-3 s-1 via a custom built testing apparatus. The specimens, fabricated using e-beam evaporation, had gage sections 1000 µm long and 200 µm wide, with thickness varying between 500 and 650 nm. The specimens were fabricated as 200 nm multi-layers with 100 nm average grain size. Force and displacement data were collected and used to construct stress-strain curves. The specimens exhibited elastic-nearly perfectly plastic behavior at all strain rates excluding the slowest (10-6 s-1) where local stress peaks were observed. Material yield strength and peak stress, ranging from 120-300 MPa and 140-365 MPa respectively, both increased as the strain rate increased. For high strain rates the ductility was measured to be about 1.9%, increasing to 4.5% for the lowest strain rate. These values were found to be consistent with those published in literature. In general, the material exhibited qualitative trends as expected for the variation in strain rate except, as mentioned before, at the slowest strain rates.

Morphing Structure Technology and Its Application to Flight Control
Thomas Bliss, University of Virginia

The common goal of all aerospace advancements is safe, efficient air transportation. The current method of achieving directional stability – control surfaces such as flaps and ailerons – is heavy and inefficient. If these bulky mechanisms are replaced with an ultra-lightweight morphing structure, efficiency can be increased by cutting drag and weight. In this project, a wing section comprising trusses lining the inner lower skin is designed. Actuators replace passive members in this structure to achieve shape change. Project goals include modeling, constructing, deflection analysis, and finite element analysis of a morphing wing system. The system is built using a rapid
prototype-milling machine at the University of Virginia. A deflection analysis adapted from Lu et al’s Optimal Design of a Flexural Actuator is developed and tested to illustrate the constructed system’s performance abilities, proving that morphing structures are capable of replacing modern control systems.

Computational Studies of the Virginia Tech Hypersonic Wind Tunnel
Rui Chen, Virginia Tech

My poster presentation will display Computational Fluid Dynamics (CFD) predictions of the flowfields inside the Virginia Tech Hypersonic Wind Tunnel (VT HST) shown in Figure 1. The CFD predictions will be compared with available experimental data. The purposes of my research are to assess the quality of the flowfield inside the VT HST and to improve the understanding of its working characteristics. Both steady-state (viscous) and time-accurate (inviscid) CFD calculations were performed using AeroSoft’s GASP 4.2.1. I found that the pressure ratios (the total pressure in the settling chamber divided by the back pressure at the diffuser exit) required to start the VT HST in steady-state calculations are much higher than those required to start the real tunnel. Since wind tunnel flow is inherently a time-dependent phenomenon, I ran 2nd order time-accurate calculations for the VT HST with a Mach 4 nozzle. Although the calculations are still in progress, it seems that the VT HST can start at the correct pressure ratio in time-accurate calculations. In addition to the steady-state flowfields, I will also be able study the wind tunnel starting process once my time-accurate calculations are complete.

Space Communications and High Altitude Earth Observation
Stargel Doane, Old Dominion University

The principles surrounding space communications and high altitude earth observation are both fascinating and complex. To better understand this topic, a satellite ground station was constructed on the campus of Old Dominion University. It has the ability to automatically track, record, and decode NOAA weather satellite transmissions and communicate with other parts of the world via amateur radio satellites. The satellite ground station has been assembled from individual electronic components, each with an intended purpose. The collection of weather satellite images has been taking place over the past ten months, and all data is accessible through a searchable database on the world wide web. Since the satellite ground station is only one aspect of a space communications system, a simple remote sensing vehicle is currently being constructed. This vehicle is in fact a high altitude balloon, which when completed, will have the ability to record temperature and pressure variations in the earth’s atmosphere and take high altitude earth images. This balloon is projected to reach altitudes of approximately 90,000 feet. All of the collected data will be continuously transmitted to the satellite ground station, thus illustrating a simple but complete space communications system.

Quantification Of Phenomena Observed During A Single Event Upset Test On A Recoverable Flight Control Computer
Matthew Ferguson, Old Dominion University

This paper quantifies the phenomena observed during a Single Event Upset (SEU) test performed on a recoverable flight control computer (FCC) at Los Alamos Neutron Scattering Science Center (LANSCE). The FCC unit consisted of an Airplane Information Management System (AIMS) connected to a prototype roll-back recovery system. Both of these units were part of a larger closed-loop system controlled by a B737 flight emulator. Because of the high neutron flux at LANSCE, a very accelerated life test of the system was performed with a neutron energy spectrum
similar to that which an operational aircraft would encounter during flight. The phenomena that were observed during the test included rollback recoveries, operating system reboots, CPU idle periods with no I/O and loss of data synchronization within the computer. It is presumed that these phenomena were induced by the neutrons.

Sensible Heat Flux
Randy Scott, Hampton University

For my research project, my objective is to estimate sensible heat flux amounts in the Hampton Roads area. My research will demonstrate the basic concepts of Sensible Heat Flux, the amount of heat transferred into the atmosphere, per unit of time through a unit area. Heat Flux - is the process by which the air gets warmer every day. In order to estimate the heat flux amounts in the area, I have been using data from the Modis Aqua and Terra satellites. The atmospheric data that I am using to make estimates are Surface Temperature, Solar Radiation, Wind Speed, Air Temperature, and Leaf Area Index. For this particular research project, I will show results for sensible heat flux patterns in the Hampton Roads Area. The study that I am conducting is for the summer of 2003, thus I will make a plot that represents the sensible heat flux patterns for each month of the summer. Once required data have been gathered, the Analytical Land-Atmosphere Radiometric Model (ALARM) will be used to convert radiometric land surface temperature to isothermal surface temperature to successfully evaluate heat flux in each particular area.

Rotor Design For An Unmanned Helicopter For Use On Mars
Timothy Streett, Virginia Tech

This project is a detailed investigation on rotors in rarefied atmosphere. It focuses on an analytical determination of the optimum configuration to lift a 100 kg payload effectively in Martian atmosphere. A simplified actuator disc model was used to get a ballpark power requirement to determining the overall feasibility of the concept. A more detailed blade element analysis will be used to determine the overall capability of the system. Using highly idealized equations as a starting point for velocities at selected control points, more detailed analyses determine the theoretical capabilities of various selected airfoil designs for each rotor configuration. Airfoils will be selected based on published performance characteristics. The design constraints for size will be taken from the dimensions of the current Martian lander aero shells. The aerodynamic design will focus on keeping the tip-speed subsonic to avoid shock problems. After the single rotor is defined, it will be examined in a co-axial configuration to show the benefits of that design choice over other options.

MicroMAPS Modeling and Data Reduction
Steven Tangen, University of Virginia

MicroMAPS (Microprocessor-based Measurement of Air Pollution from Satellite) is a second-generation gas filter correlation radiometer that measures carbon monoxide levels in the troposphere. Previous work centered on the construction of a theoretical model to predict instrument behavior at a given instrument state with prescribed atmospheric conditions. This paper details the refinement of that model with a focus on instrument test flights on board the Proteus high altitude research aircraft during Summer 2004. Several modifications including temperature shifts were made that improved accuracy and increased relevancy to the test flights. Also outlined is the theory behind the averaging kernel sensitivity tool. The averaging kernel is calculated and validated against previous in situ readings taken during flights of the precursor MAPS instrument. Compared to the weighted vertical profiles produced by MAPS, the MicroMAPS averaging kernel differed by approximately 3% thus proving its effectiveness as a data reduction tool.

Mechanical Characterization Of Gold Thin Films For Rf-Mems
Katherine Timpano, University of Virginia

Evaporated and electroplated freestanding gold films have been tested to determine their mechanical properties, specifically yield strength, ultimate strength, and ductility. The evaporated specimens were fabricated at two thicknesses, 0.5 and 0.65 microns, on a silicon substrate, and the electroplated specimens were deposited 2.5 microns thick on a quartz substrate. The films were loaded in a uniaxial microtensile tester at varying strain rates (10-2 - 10-6 s-1) until failure. A finite element model of the specimen was used in conjunction with the displacement data to determine the strain imposed on the film, and these values were used to derive stress-strain curves. The electroplated specimens demonstrated a much higher ductility for the same strain rate than the evaporated specimens, with the ductility for the evaporated films varying from 2.0-4.7% for strain rates from 10-3-10-6 s-1 and the electroplated from 5.6-10.6% ductility for similar strain rates. Yield and ultimate strength values were similar for the two fabrication techniques, and ultimate strength increased substantially with thickness for evaporated specimens. These films have applications in radio-frequency MEMS devices for use in space systems.

Pressure-Sensitive Paint: Practical Application In Wind Tunnels
Errol Yuksek, Old Dominion University

The use of Pressure Sensitive Paint (PSP) is one of the most effective methods of pressure measurement. Effective both on simple and complex surfaces, PSP can produce global surface pressure maps with exceptional spatial resolution. However, there are practical issues that hinder its accuracy. Surface preparation and paint application is tedious, expensive, and time consuming. Sensitivity to temperature is also an issue since it affects luminescent molecules and their transitions. Research has focused on developing self-adhesive tape or decals, pre-coated with PSP material. One advantage to this approach would be quick and easy application to areas of interest during experimentation. This would not only minimize cost and surface preparation time but, at the same time, unveil a solution to the issue of PSP degradation. Should the PSP degrade from use or handling, one would need only to quickly remove and re-apply a new strip of PSP coated tape. Due to the more controlled conditions under which the tapes would be prepared, it would also be possible to apply dual coatings. An example would be to have a stripe of PSP along with a parallel stripe of Temperature Sensitive Paint. This would grant the ability to determine relative temperature and pressure measurements on a given surface, and adjust pressure measurements accordingly.