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NASA NTRS2010

Algorithm for Lossless Compression of Calibrated Hyperspectral Imagery

A two-stage predictive method was developed for lossless compression of calibrated hyperspectral imagery. The first prediction stage uses a conventional linear predictor intended to exploit spatial and/or spectral dependencies in the data. The compressor tabulates counts of the past values of the difference between this initial prediction and the actual sample value. To form the ultimate predicted value, in the second stage, these counts are combined with an adaptively updated weight function intended to capture information about data regularities introduced by the calibration process. Finally, prediction residuals are losslessly encoded using adaptive arithmetic coding. Algorithms of this type are commonly tested on a readily available collection of images from the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) hyperspectral imager. On the standard calibrated AVIRIS hyperspectral images that are most widely used for compression benchmarking, the new compressor provides more than 0.5 bits/sample improvement over the previous best compression results. The algorithm has been implemented in Mathematica. The compression algorithm was demonstrated as beneficial on 12-bit calibrated AVIRIS images.

Kiely, Aaron B.↗

NASA NTRS1996

Improving the Performance of the Structure-Based Connectionist Network for Diagnosis of Helicopter Gearboxes

A diagnostic method is introduced for helicopter gearboxes that uses knowledge of the gear-box structure and characteristics of the 'features' of vibration to define the influences of faults on features. The 'structural influences' in this method are defined based on the root mean square value of vibration obtained from a simplified lumped-mass model of the gearbox. The structural influences are then converted to fuzzy variables, to account for the approximate nature of the lumped-mass model, and used as the weights of a connectionist network. Diagnosis in this Structure-Based Connectionist Network (SBCN) is performed by propagating the abnormal vibration features through the weights of SBCN to obtain fault possibility values for each component in the gearbox. Upon occurrence of misdiagnoses, the SBCN also has the ability to improve its diagnostic performance. For this, a supervised training method is presented which adapts the weights of SBCN to minimize the number of misdiagnoses. For experimental evaluation of the SBCN, vibration data from a OH-58A helicopter gearbox collected at NASA Lewis Research Center is used. Diagnostic results indicate that the SBCN is able to diagnose about 80% of the faults without training, and is able to improve its performance to nearly 100% after training.

Jammu, Vinay B.↗

NASA NTRS1990

The fundamentals of adaptive grid movement

Basic grid point movement schemes are studied. The schemes are referred to as adaptive grids. Weight functions and equidistribution in one dimension are treated. The specification of coefficients in the linear weight, attraction to a given grid or a curve, and evolutionary forces are considered. Curve by curve and finite volume methods are described. The temporal coupling of partial differential equations solvers and grid generators was discussed.

Eiseman, Peter R.↗

NASA NTRS1991

Towards practical control design using neural computation

The objective is to develop neural network based control design techniques which address the issue of performance/control effort tradeoff. Additionally, the control design needs to address the important issue if achieving adequate performance in the presence of actuator nonlinearities such as position and rate limits. These issues are discussed using the example of aircraft flight control. Given a set of pilot input commands, a feedforward net is trained to control the vehicle within the constraints imposed by the actuators. This is achieved by minimizing an objective function which is the sum of the tracking errors, control input rates and control input deflections. A tradeoff between tracking performance and control smoothness is obtained by varying, adaptively, the weights of the objective function. The neurocontroller performance is evaluated in the presence of actuator dynamics using a simulation of the vehicle. Appropriate selection of the different weights in the objective function resulted in the good tracking of the pilot commands and smooth neurocontrol. An extension of the neurocontroller design approach is proposed to enhance its practicality.

Troudet, Terry↗

NASA NTRS1999

Time course of myosin heavy chain transitions in neonatal rats: importance of innervation and thyroid state

During the postnatal period, rat limb muscles adapt to weight bearing via the replacement of embryonic (Emb) and neonatal (Neo) myosin heavy chains (MHCs) by the adult isoforms. Our aim was to characterize this transition in terms of the six MHC isoforms expressed in skeletal muscle and to determine the importance of innervation and thyroid hormone status on the attainment of the adult MHC phenotype. Neonatal rats were made hypothyroid via propylthiouracil (PTU) injection. In normal and PTU subgroups, leg muscles were unilaterally denervated at 15 days of age. The MHC profiles of plantaris (PLN) and soleus (Sol) muscles were determined at 7, 14, 23, and 30 days postpartum. At day 7, the Sol MHC profile was 55% type I, 30% Emb, and 10% Neo; in the PLN, the pattern was 60% Neo and 25% Emb. By day 30 the Sol and PLN had essentially attained an adult MHC profile in the controls. PTU augmented slow MHC expression in the Sol, whereas in the PLN it markedly repressed IIb MHC by retaining neonatal MHC expression. Denervation blunted the upregulation of IIb in the PLN and of Type I in the Sol and shifted the pattern to greater expression of IIa and IIx MHCs in both muscles. In contrast to previous observations, these findings collectively suggest that both an intact thyroid and innervation state are obligatory for the attainment of the adult MHC phenotype, particularly in fast-twitch muscles.

Non-NASA Center↗

NASA NTRS2004

Investigation of Injector Slot Geometry on Curved-Diffuser Aerodynamic Performance

The Compressor Branch vision is to be recognized as world-class leaders in research for fluid mechanics of compressors. Its mission is to conduct research and develop technology to advance the state of the art of compressors and transfer new technology to U.S. industries. Maintain partnerships with U.S. industries, universities, and other government organizations. Maintain a balance between customers focused and long range research. Flow control comprises enabling technologies to meet compression system performance requirements driven by emissions and fuel reduction goals (e.g., in UEET), missions (e.g., access-to-space), aerodynamically aggressive vehicle configurations (e.g., UAV and future blended wing body configurations with highly distorted inlets), and cost goals (e.g., in VAATE). The compression system requirements include increased efficiency, power-to-weight, and adaptability (i.e., robustness in terms of wide operability, distortion tolerance, and engine system health and reliability). The compressor flow control task comprises efforts to develop, demonstrate, and transfer adaptive flow control technology to industry to increase aerodynamic loading at current blade row loss levels, to enable adaptive1 y wide operability, and to develop plant models for adaptive compression systems. In this context, flow control is the controlled modification of a flow field by a deliberate means beyond the natural (uncontrolled) shaping of the solid surfaces that define the principal flow path. The objective of the compressor flow control task is to develop and apply techniques that control circulation, aerodynamic blockage, and entropy production in order to enhance the performance and operability of compression systems for advanced aero-propulsion applications. This summer I would be working with a curved-diffuser because it simulates what happens with flow in the stator blades in the compressor. With this experiment I will be doing some data analysis and parametric study of the injector slot geometries to get the best aerodynamic performance of it. This includes some data reduction, redesign and fast prototyping of the injector nozzle.

Silva, Odlanier↗

NASA NTRS2009

Pixelized Device Control Actuators for Large Adaptive Optics

A fully integrated, compact, adaptive space optic mirror assembly has been developed, incorporating new advances in ultralight, high-performance composite mirrors. The composite mirrors use Q-switch matrix architecture-based pixelized control (PMN-PT) actuators, which achieve high-performance, large adaptive optic capability, while reducing the weight of present adaptive optic systems. The self-contained, fully assembled, 11x11x4-in. (approx.= 28x28x10-cm) unit integrates a very-high-performance 8-in. (approx.=20-cm) optic, and has 8-kHz true bandwidth. The assembled unit weighs less than 15 pounds (=6.8 kg), including all mechanical assemblies, power electronics, control electronics, drive electronics, face sheet, wiring, and cabling. It requires just three wires to be attached (power, ground, and signal) for full-function systems integration, and uses a steel-frame and epoxied electronics. The three main innovations are: 1. Ultralightweight composite optics: A new replication method for fabrication of very thin composite 20-cm-diameter laminate face sheets with good as-fabricated optical figure was developed. The approach is a new mandrel resin surface deposition onto previously fabricated thin composite laminates. 2. Matrix (regenerative) power topology: Waveform correction can be achieved across an entire face sheet at 6 kHz, even for large actuator counts. In practice, it was found to be better to develop a quadrant drive, that is, four quadrants of 169 actuators behind the face sheet. Each quadrant has a single, small, regenerative power supply driving all 169 actuators at 8 kHz in effective parallel. 3. Q-switch drive architecture: The Q-switch innovation is at the heart of the matrix architecture, and allows for a very fast current draw into a desired actuator element in 120 counts of a MHz clock without any actuator coupling.

Knowles, Gareth J.↗

NASA NTRS1917

Thermodynamic efficiency of present types of internal combustion engines for aircraft

Report presents requirements of internal combustion engines suitable for aircraft. Topics include: (1) service requirements for aeronautic engines - power versus weight, reliability, and adaptability factors, (2) general characteristics of present aero engines, (3) aero engine processes and functions of parts versus power-weight ratio, reliability, and adaptability factors, and (4) general arrangement, form, proportions, and materials of aero parts - power-weight ratio, reliability, and adaptability.

Lucke, Charles E↗

NASA NTRS1984

Mass discrimination during prolonged weightlessness

Thresholds for mass discrimination under zero gravity in flight were found to be higher by a factor of about 1.8 than those for weight discrimination before flight. This suggests that humans are not as sensitive to inertial mass as they are to weight, and that adaptation can only partially compensate for loss of gravity. Weight discrimination thresholds were raised for 2 or 3 days after flight, suggesting an aftereffect of adaptation to weightlessness.

Ross, H.↗

NASA NTRS1990

A three-dimensional dynamic solution-adaptive mesh algorithm

A solution-adaptive grid algorithm has been developed for use in two and three dimensions. The algorithm uses a transformation from the cartesian coordinate system to a general coordinate space, which will be defined as a parallelepiped. A weighting function for adaption of the grid is developed that will allow adaption to the gradients of any combination of dependent variables in the flow. The adaption is carried out in the parametric space and a simple inverse mapping to return the new parametric space to the physical space is derived. The concept used to relocate the grid-points in the parametric space is based on the center of mass of distributed weights. Solution-adaptive results are presented for various laminar flows in two dimensions and for mathematical weighting functions in three dimensions.

Benson, Rusty A.↗

NASA NTRS1985

Multiple-User Adaptive-Array Communication System

Weights for K-beam system computed K/6 times faster. In single-frequency adaptive-array communication system in whick K mobile users communicate with central station equipped with n-antenna array. Each K signal recoverable by taking specific weighted sum of n complex antenna voltages.

Zohar, S.↗

NASA NTRS2002

Metallic Thermal Protection System Technology Development: Concepts, Requirements and Assessment Overview

A technology development program was conducted to evolve an earlier metallic thermal protection system (TPS) panel design, with the goals of: improving operations features, increasing adaptability (ease of attaching to a variety of tank shapes and structural concepts), and reducing weight. The resulting Adaptable Robust Metallic Operable Reusable (ARMOR) TPS system incorporates a high degree of design flexibility (allowing weight and operability to be traded and balanced) and can also be easily integrated with a large variety of tank shapes, airframe structural arrangements and airframe structure/material concepts. An initial attempt has been made to establish a set of performance based TPS design requirements. A set of general (FARtype) requirements have been proposed, focusing on defining categories that must be included for a comprehensive design. Load cases required for TPS design must reflect the full flight envelope, including a comprehensive set of limit loads, However, including additional loads. such as ascent abort trajectories, as ultimate load cases, and on-orbit debris/micro-meteoroid hypervelocity impact, as one of the discrete -source -damage load cases, will have a significant impact on system design and resulting performance, reliability and operability. Although these load cases have not been established, they are of paramount importance for reusable vehicles, and until properly included, all sizing results and assessments of reliability and operability must be considered optimistic at a minimum.

Dorsey, John T.↗

NASA NTRS1992

Changes in skeletal muscle gene expression consequent to altered weight bearing

Skeletal muscle is a dynamic organ that adapts to alterations in weight bearing. This brief review examines changes in muscle gene expression resulting from the removal of weight bearing by hindlimb suspension and from increased weight bearing due to eccentric exercise. Acute (less than or equal to 2 days) non-weight bearing of adult rat soleus muscle alters only the translational control of muscle gene expression, while chronic (greater than or equal to 7 days) removal of weight bearing appears to influence pretranslational, translational, and posttranslational mechanisms of control. Acute and chronic eccentric exercise are associated with alterations of translational and posttranslational control, while chronic eccentric training also alters the pretranslational control of muscle gene expression. Thus alterations in weight bearing influence multiple sites of gene regulation.

NASA Discipline Musculoskeletal↗

NASA NTRS1985

Analysis of adaptive algorithms for an integrated communication network

Techniques were examined that trade communication bandwidth for decreased transmission delays. When the network is lightly used, these schemes attempt to use additional network resources to decrease communication delays. As the network utilization rises, the schemes degrade gracefully, still providing service but with minimal use of the network. Because the schemes use a combination of circuit and packet switching, they should respond to variations in the types and amounts of network traffic. Also, a combination of circuit and packet switching to support the widely varying traffic demands imposed on an integrated network was investigated. The packet switched component is best suited to bursty traffic where some delays in delivery are acceptable. The circuit switched component is reserved for traffic that must meet real time constraints. Selected packet routing algorithms that might be used in an integrated network were simulated. An integrated traffic places widely varying workload demands on a network. Adaptive algorithms were identified, ones that respond to both the transient and evolutionary changes that arise in integrated networks. A new algorithm was developed, hybrid weighted routing, that adapts to workload changes.

Reed, Daniel A.↗

NASA NTRS1991

An experimental SMI adaptive antenna array simulator for weak interfering signals

An experimental sample matrix inversion (SMI) adaptive antenna array for suppressing weak interfering signals is described. The experimental adaptive array uses a modified SMI algorithm to increase the interference suppression. In the modified SMI algorithm, the sample covariance matrix is redefined to reduce the effect of thermal noise on the weights of an adaptive array. This is accomplished by subtracting a fraction of the smallest eigenvalue of the original covariance matrix from its diagonal entries. The test results obtained using the experimental system are compared with theoretical results. The two show a good agreement.

Dilsavor, Ronald S.↗

NASA NTRS2004

Fabrication and Testing of Active and Adaptive Cyanate Ester Composite Mirrors

The objective of the NASA/Bennett Optical Research Inc. (BOR) NAS8-02008 Phase II Program, which also incorporated ideas developed under the earlier NASA NAS8-01035 Phase 1 Program, was to develop a large mirror fabrication and test facility with emphasis on producing large, light weight active and adaptive optics. A principle objective was to develop mandrels on which to make large composite graphite-filled cyanate ester mirrors, Deliverables were two of these superpolished lightweight active/adaptive optic composite mirrors, one 12" (approx.1/3 meter) in diameter and one 22" (approx.1/2 meter) in diameter. In addition optical superpolishers for mandrels up to 1.2 meters in diameter, test instruments for determining optical figure and scattered light, novel design actuators for making the composite mirrors both active and adaptive, and passive and active means for measuring actuator performance were developed at BOR. We are now installing a superpolisher capable of producing 3 meter diameter mirror/mandrels. All polishers utilize the principle of centrifugal elutriation and produce superpolished mandrels with surface microroughnesses under 1 nm rms.

Bennett, H. E.↗

NASA NTRS1988

Adaptive Control For Space-Station Joints

Input gain weighting added to existing adaptive-control algorithm. Report discusses concept for adaptive control of rotations of various appended structures about joints on space station, with suppression of vibrations in both station and appendages. Concept relevant to such terrestrial applications as control of aircraft, suppression of vibrations in large buildings, and robotics.

Ih, Che-Hang Charles↗

NASA NTRS2007

Thin, nearly wireless adaptive optical device

A thin, nearly wireless adaptive optical device capable of dynamically modulating the shape of a mirror in real time to compensate for atmospheric distortions and/or variations along an optical material is provided. The device includes an optical layer, a substrate, at least one electronic circuit layer with nearly wireless architecture, an array of actuators, power electronic switches, a reactive force element, and a digital controller. Actuators are aligned so that each axis of expansion and contraction intersects both substrate and reactive force element. Electronics layer with nearly wireless architecture, power electronic switches, and digital controller are provided within a thin-film substrate. The size and weight of the adaptive optical device is solely dominated by the size of the actuator elements rather than by the power distribution system.

Knowles, Gareth↗