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At least 199 records · Page 11

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NASA NTRS2004

Theoretical Evaluation of Electroactive Polymer Based Micropump Diaphragm for Air Flow Control

An electroactive polymer (EAP), high energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) [P(VDFTrFE)] copolymer, based actuation micropump diaphragm (PAMPD) have been developed for air flow control. The displacement strokes and profiles as a function of amplifier and frequency of electric field have been characterized. The volume stroke rates (volume rate) as function of electric field, driving frequency have been theoretically evaluated, too. The PAMPD exhibits high volume rate. It is easily tuned with varying of either amplitude or frequency of the applied electric field. In addition, the performance of the diaphragms were modeled and the agreement between the modeling results and experimental data confirms that the response of the diaphragms follow the design parameters. The results demonstrated that the diaphragm can fit some future aerospace applications to replace the traditional complex mechanical systems, increase the control capability and reduce the weight of the future air dynamic control systems. KEYWORDS: Electroactive polymer (EAP), micropump, diaphragm, actuation, displacement, volume rate, pumping speed, clamping ratio.

Xu, Tian-Bing↗

NASA NTRS2004

Development of a Solid-Oxide Fuel Cell/Gas Turbine Hybrid System Model for Aerospace Applications

Recent interest in fuel cell-gas turbine hybrid applications for the aerospace industry has led to the need for accurate computer simulation models to aid in system design and performance evaluation. To meet this requirement, solid oxide fuel cell (SOFC) and fuel processor models have been developed and incorporated into the Numerical Propulsion Systems Simulation (NPSS) software package. The SOFC and reformer models solve systems of equations governing steady-state performance using common theoretical and semi-empirical terms. An example hybrid configuration is presented that demonstrates the new capability as well as the interaction with pre-existing gas turbine and heat exchanger models. Finally, a comparison of calculated SOFC performance with experimental data is presented to demonstrate model validity. Keywords: Solid Oxide Fuel Cell, Reformer, System Model, Aerospace, Hybrid System, NPSS

Freeh, Joshua E.↗

NASA NTRS2003

Nonlinear Flutter Aspects of the Flexible HSCT Semispan Model

The nonlinear aspects that lead to the flutter of an High-Speed Civil Transport (HSCT) Flexible Semispan Model are analyzed. A hierarchy of spectral moments was used to determine the characteristics of the aerodynamic loading and structural strains and motions. The results show that the frequency of the bending motion of the wing varied significantly as the Mach number was increased between 0.90 and 0.97. Examination of the pressure coefficients in terms of mean value and fluctuations showed that the flow characteristics over the wing changed significantly around a Mach number of 0.97. A strong shock was identified near the trailing edge. Nonlinear analysis of the pressure fluctuations, under these conditions, showed nonlinear coupling involving low-frequency components at pressure locations where the mean value was at a local minimum. This shows that the aerodynamic forces acting on the model had nonlinearly coupled frequency components. The results presented here show how nonlinear analysis tools can be used to identify nonlinear aspects of the flutter phenomenon which are needed in the validation of nonlinear computational methodologies. Keywords: Nonlinear aeroelasticity, Flutter, Bispectrum.

Hajj, Muhammad R.↗

NASA NTRS1999

A Deployable Primary Mirror for Space Telescopes

NASA Langley Research Center, Composite Optics, Inc., and Nyma/ADF have developed jointly a deployable primary mirror for space telescopes that combines over five years of research on deployment of optical-precision structures and over ten years of development of fabrication techniques for optical-precision composite mirror panels and structures. The deployable mirror is directly applicable to a broad class of non-imaging "lidar" (light direction a nd ranging) telescopes whose figure-error requirements are in the range of one to ten microns RMS. Furthermore, the mirror design can be readily modified to accommodate imaging-quality reflector panels and active panel-alignment control mechanisms for application to imaging telescopes. The present paper: 1) describes the deployable mirror concept; 2) explains the status of the mirror development; and 3) provides some technical specifications for a 2.55- m-diameter, proof-of-concept mirror. Keywords: precision deployment, hinge joint, latch joint, deployable structures, fabrication, space telescopes, optical instruments, microdynamics.

Lake, Mark S.↗

NASA NTRS1999

Point Response Characteristics for the CERES/EOS-PM, FM3 & FM4 instruments.

This paper describes the point source functions (PSF s) of the Clouds and the Earth s Radiant Energy System (CERES,) Earth Observing System (EOS,) afternoon platform (PM,) Flight Model 3 (FM3,) and Flight Model 4 (FM4) scanning instruments. The PSF (also known as the Point Response Function, or PRF) is vital to the accurate geo-location of the remotely sensed radiance measurements acquired by the instrument. This paper compares the characteristics of the FM3 and FM4 instruments with the earlier Proto Flight Model (PFM) on the Tropical Rainfall Measuring Mission (TRMM) platform, and the FM1 and FM2 Models on the EOS morning orbiting (AM) platform, which has recently been renamed "Terra". All of the PSF s were found to be quite comparable, and the previously noted "spreading" characteristic of the window (water vapor) channel PSF is analyzed Keywords: PSF, PRF, CERES, TRMM, EOS, Earth Radiation Budget

Paden, Jack↗

NASA NTRS2004

Digital Archive Issues from the Perspective of an Earth Science Data Producer

Contents include the following: Introduction. A Producer Perspective on Earth Science Data. Data Producers as Members of a Scientific Community. Some Unique Characteristics of Scientific Data. Spatial and Temporal Sampling for Earth (or Space) Science Data. The Influence of the Data Production System Architecture. The Spatial and Temporal Structures Underlying Earth Science Data. Earth Science Data File (or Relation) Schemas. Data Producer Configuration Management Complexities. The Topology of Earth Science Data Inventories. Some Thoughts on the User Perspective. Science Data User Communities. Spatial and Temporal Structure Needs of Different Users. User Spatial Objects. Data Search Services. Inventory Search. Parameter (Keyword) Search. Metadata Searches. Documentation Search. Secondary Index Search. Print Technology and Hypertext. Inter-Data Collection Configuration Management Issues. An Archive View. Producer Data Ingest and Production. User Data Searching and Distribution. Subsetting and Supersetting. Semantic Requirements for Data Interchange. Tentative Conclusions. An Object Oriented View of Archive Information Evolution. Scientific Data Archival Issues. A Perspective on the Future of Digital Archives for Scientific Data. References Index for this paper.

Barkstrom, Bruce R.↗

NASA NTRS1998

Overview of Active Flow Control at NASA Langley Research Center

The paper summarizes Active Flow Control projects currently underway at the NASA Langley Research Center. Technology development is being pursued within a multidisciplinary, cooperative approach, involving the classical disciplines of fluid mechanics, structural mechanics, material science, acoustics, and stability and control theory. Complementing the companion papers in this session, the present paper will focus on projects that have the goal of extending the state-of-the-art in the measurement, prediction, and control of unsteady, nonlinear aerodynamics. Toward this goal, innovative actuators, micro and macro sensors, and control strategies are considered for high payoff flow control applications. The target payoffs are outlined within each section below. Validation of the approaches range from bench-top experiments to wind-tunnel experiments to flight tests. Obtaining correlations for future actuator and sensor designs are implicit in the discussion. The products of the demonstration projects and design tool development from the fundamental NASA R&D level technology will then be transferred to the Applied Research components within NASA, DOD, and US Industry. Keywords: active flow control, separation control, MEMS, review

Pack, L. G.↗

NASA NTRS1995

Interferometric Tomographic Measurement of an Instataneous Flow Field Under Adverse Environments

Measurement of an instantaneous flow field by interferometric tomography, that is, reconstruction of a three-dimensional refractive-index field from multi-directional projection data, has been conducted. In order to simulate the expected experimental arrangement at a wind tunnel, reconstructions are made from a restricted view angle less than 40 degrees and incomplete projections. In addition, appreciable ambient air and experimental setup disturbances are present. A new phase-stepping technique, based on a generalized phase-stepping approach of a four-bucket model, is applied for expeditious and accurate phase information extraction from projection interferograms under the harsh environments. Phase errors caused by the various disturbances, which can include ambient refractive-index change, optical component disturbance, hologram repositioning error, etc., are partially compensated with a linear corrective model. A new computational tomographic technique based on a series expansion approach was also utilized to efficiently deal with arbitrary boundary shapes and the continuous flow fields in reconstruction. The results of the preliminary investigation are encouraging; however, the technique needs to be further developed in the future through refinement of the approaches reported here and through hybridization with previously developed techniques. Keywords: interferometry, tomography, phase stepping

Yu, En-Xi↗

NASA NTRS2004

New Evidence for the Presence of Indigenous Microfossils in Carbonaceous Chondrites

We present additional evidence for the presence of indigenous microfossils in carbonaceous meteorites scanning electron micrograph studies of freshly fractured interior surfaces of pristine samples of the Murchison CM2 carbonaceous meteorite have revealed forms in-situ that are recognizable as biofilms as well as complex and highly structured forms similar to calcareous and siliceous microfossils. Some of the forms encountered are very well-preserved and exhibit complex associated microstructures similar to bacterial flagella. New images will be presented of forms recently encountered in carbonaceous meteorites and they will be compared with those of known microbial extremophiles. KEYWORDS: carbonaceous chondrites, Murchison, microfossils, extremophiles

Hoover, Richard B.↗

NASA NTRS2004

Biologically Derived Nanoparticle Arrays via a Site-Specific Reconstitution of Ferritin and their Electrochemistry

Nanoparticle arrays biologically derived from an electrochemically-controlled site-specific biomineralization were fabricated on a gold substrate through the immobilization process of biomolecules. The work reported herein includes the immobilization of ferritin with various surface modifications, the electrochemical biomineralization of ferritins with different inorganic cores, the fabrication of self-assembled arrays with the immobilized ferritin, and the electrochemical characterization of various core materials. Protein immobilization on the substrate is achieved by anchoring ferritins with dithiobis-N-succinimidyl propionate (DTSP). A reconstitution process of electrochemical site-specific biomineralization with a protein cage loads ferritins with different core materials such as Pt, Co, Mn, and Ni. The ferritin acts as a nano-scale template, a biocompatible cage, and a separator between the nanoparticles. The nano-sized metalcored ferritins on a gold substrate displayed a good electrochemical activity for the electron transport and storage, which is suitable for bioelectronics applications such as biofuel cell, bionanobattery, biosensors, etc. Keywords: Ferritin, immobilization, site-specific reconstitution, biomineralization, and bioelectronics

Kim, Jae-Woo↗

NASA NTRS2004

Comparison of Measured Galactic Background Radiation at L-Band with Model

Radiation from the celestial sky in the spectral window at 1.413 GHz is strong and an accurate accounting of this background radiation is needed for calibration and retrieval algorithms. Modern radio astronomy measurements in this window have been converted into a brightness temperature map of the celestial sky at L-band suitable for such applications. This paper presents a comparison of the background predicted by this map with the measurements of several modern L-band remote sensing radiometer Keywords-Galactic background, microwave radiometry; remote sensing;

LeVine, David M.↗

NASA NTRS2004

Microshutter Arrays for James Webb Space Telescope

Two-dimensional MEMS microshutter arrays are being developed at NASA Goddard Space Flight Center for use in the near-infrared region on the James Webb Space Telescope (JWST). The microshutter arrays are designed for the selective transmission of light with high efficiency and high contrast. The JWST environment requires cryogenic operation at 35K. Microshutter arrays are fabricated out of silicon-oxide-insulated (SOI) silicon wafers. Arrays are close-packed silicon nitride membranes with a pixel size of 100x200 p. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with a minimized mechanical stress concentration. The mechanical shutter arrays are fabricated using MEMS technologies. The processing includes a multi- layer metal deposition and patterning of shutter electrodes and magnetic pads, reactive ion etching (NE) of the front side to form shutters out of the nitride membrane, an anisotropic back-etch for wafer thinning, followed by a deep RIE (DRIE) back-etch down to the nitride shutter membrane to form W e s and relieve shutters from the silicon substrate. An additional metal deposition and patterning is used to form back electrodes. Shutters are actuated using a magnetic force and latched using an electrostatic force. . . . KEYWORDS: microshutter, MEMS, RIE, DRIE, micro-optics, near inbred, space telescope

Li, Mary J.↗

NASA NTRS2001

Delivering Faster Congestion Feedback with the Mark-Front Strategy

Computer networks use congestion feedback from the routers and destinations to control the transmission load. Delivering timely congestion feedback is essential to the performance of networks. Reaction to the congestion can be more effective if faster feedback is provided. Current TCP/IP networks use timeout, duplicate Acknowledgement Packets (ACKs) and explicit congestion notification (ECN) to deliver the congestion feedback, each provides a faster feedback than the previous method. In this paper, we propose a markfront strategy that delivers an even faster congestion feedback. With analytical and simulation results, we show that mark-front strategy reduces buffer size requirement, improves link efficiency and provides better fairness among users. Keywords: Explicit Congestion Notification, mark-front, congestion control, buffer size requirement, fairness.

Liu, Chunlei↗

NASA NTRS2004

Verifying Multi-Agent Systems via Unbounded Model Checking

We present an approach to the problem of verification of epistemic properties in multi-agent systems by means of symbolic model checking. In particular, it is shown how to extend the technique of unbounded model checking from a purely temporal setting to a temporal-epistemic one. In order to achieve this, we base our discussion on interpreted systems semantics, a popular semantics used in multi-agent systems literature. We give details of the technique and show how it can be applied to the well known train, gate and controller problem. Keywords: model checking, unbounded model checking, multi-agent systems

Kacprzak, M.↗

NASA NTRS2003

EU Accession and Civil Aviation Regimes: Malta and Cyprus as a Case Study

Aviation deregulation is usually a challenging and demanding task and accession to the European Union requires that all candidate states should harmonize their legislation in the context of the European Common Aviation Area. Malta and Cyprus, the small Mediterranean island-states to join the EU in 2004, will have to abandon any protectionist policies in favour of their flag-carriers and let them survive in a liberal framework. The paper discusses the implications of this regime change for civil aviation in Malta and Cyprus and in addition to the airline industry, it examines the impacts on the complementary tourism sector. Unless carrying capacity limits are understood, the islands may become victims of successful airline liberalisation. The paper concludes by stressing the need for sustainable development and active policy making. Keywords: carrying capacity, Cyprus, air transport deregulation, Malta, tourism

Papatheodorou, Andreas↗

NASA NTRS2003

Using Simulations to Investigate Decision Making in Airline Operations

This paper examines a range of methods to collect data for the investigation of decision-making in airline Operations Control Centres (OCCs). A study was conducted of 52 controllers in five OCCs of both domestic and international airlines in the Asia-Pacific region. A range of methods was used including: surveys, interviews, observations, simulations, and think-aloud protocol. The paper compares and evaluates the suitability of these techniques for gathering data and provides recommendations on the application of simulations. Keywords Data Collection, Decision-Making, Research Methods, Simulation, Think-Aloud Protocol.

Bruce, Peter J.↗

NASA NTRS2003

Major Impact of Fleet Renewal Over Airports Located in the Most Important Region of Brazil

The present article discusses and analyses the major impacts of the Brazilian carriers fleet renewal regarding Brazilian airport infrastructure in the most important region of the country, the Southeast (SE). A brief historical overview of the country's airline fleet will be presented, demonstrating the need for its renewal (m fact, Brazilian carriers started a major fleet renewal program m the last five years), while analyzing the periods in which a new breed of aircraft was put into service by the major carriers operating in the SE region. The trend of operating the classic regional jets plus the forthcoming entry into service of the "large regional jets" (LRJ, 70-115 seaters) in several point-to-point routes are presented along with the country's carriers" reality of operating these former aircraft in several high-capacity and medium-range routes. The article will focus on the ability of four of the major Southeast's airports to cope with the fleet modernization, mainly due to the fact that the region studied is the most socioeconomic developed, by far, with the largest demand for air transportation, thus making the impacts much more perceptible for the communities and the airport management involved. With the emergence of these impacts, several new projects and investments are being discussed and pushed forward, despite budgetary constrains being a reality in almost every Brazilian city, even in the SE region. In view of this, the paper presents how the general planning could be carried out in order to adapt the airports' infrastructures in function of the proposed (and in some cases, necessary) fleet renewal. Ultimately, we will present the present picture and two future scenarios m order to determine the level of service in the existent passenger terminal facilities in the wake of the possible operation of several new aircraft. Keywords: Airline fleet planning, Airport planning, Regional development, Regional Jets.

Maters, Rafael Waltz↗

NASA NTRS2003

Effects of the Deregulation on the Concentration of the Brazilian Air Transportation Industry

This paper addresses the effects of the deregulation of the Brazilian air transportation industry in terms of the concentration of the market. We will show some metrics that are commonly used to study the concentration of the industry. This paper uses the Herfindhal- Hirschman Index. This index tends to zero in the competitive scenario, with a large number of small firms, and to one in case of a monopolistic scenario. The paper analyses the dynamics of the concentration of the Brazilian domestic air transportation market, in order to evaluate the effects of deregulation. We conclude that the Brazilian market presents oligopoly characteristics and aspects in its current structure that maintain the market concentrated in spite of the Deregulation measures adopted by the aeronautical authority. Keywords: Herfindhal-Hirschman Index, concentration, Deregulation

Guterres, Marcelo Xavier↗