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At least 793 records · Page 44

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NASA NTRS1976

Validation of a model for investigating red cell mass changes during weightlessness

The model, both the conceptual model and simulation model, provided a convenient framework on which to demonstrate the commonality between such diverse stresses as descent from altitude, red cell infusions, bed rest, and weightlessness. The results suggest that all of these stresses induce an increased blood hematocrit leading to tissue hyperoxia and eventual inhibition of the erythyocyte producing circuit until the hyperoxic condition is relieved. The erythropoietic system was acting, in these situations, as if it were an hematocrit sensor and regulator. In these terms the decreases in red cell mass during Skylab may be explained in terms of normal feedback regulation of the erythropoietic system in the face of sustained decreases in plasma colume.

Leonard, J. I.↗

NASA NTRS1980

Stability of large horizontal-axis axisymmetric wind turbines

The stability of large horizontal-axis, axisymmetric, power producing wind turbines is examined within the framework of an analytical model which includes dynamic coupling of the rotor, tower, and power generating system. The aerodynamic loading is derived from blade element theory. Stability is determined by the eigenvalues of a set of linearized constant-coefficient differential equations. All results presented are based on a 3-bladed, 300-ft diameter, 2.0-MW wind turbine. It is shown that unstable or weakly stable behavior can be caused by aerodynamic forces due to motion of the rotor blades and tower in the plane of rotation or by mechanical coupling between the rotor system and the tower.

Hirschbein, M. S.↗

NASA NTRS1982

Nucleosynthesis in novae - A source of Ne-E and Al-26

It is shown upon computation of the nucleosynthesis products of explosive hydrogen burning, in the framework of recent nova models, that nova condensates will probably contain isotopic anomalies in Ne-22, from Na-22 decay, and Mg-26, from Al-26 decay. It is found, for all the models considered, that while too much Ne-20 and -21 is produced relative to Ne-22 to explain the presumably almost pure Ne-22 meteoritic Ne-E component, the Na-22 abundance is high enough to explain Ne-E as its decay product if nova condensates are preserved in Ne samples. It is also determined that while Al-26 is coproduced with Na-22, its total amount strongly depends on the uncertain, Si-27(p, gamma)P-28 reaction rate. The abundances of all nuclides, up to Ar, are computed and found to be clearly nonsolar in many cases.

Hillebrandt, W.↗

NASA NTRS1982

The prediction of long term viscoelastic properties of fiber reinforced plastics

A method for the experimental and analytical accelerated characterization of long term viscoelastic properties is presented. The time-temperature-stress superposition principle (TTSSP) is shown to serve as the basis for determining long term compliance data from short term creep test results. Nonlinear viscoelastic theories are discussed to provide the framework for the mathematically modeling of such a process. A time dependent Tsai-Hill-Zhurkov failure theory is used to determine long term failure properties from short term data. Compliance and failure data are incorporated in an incremental lamination theory to make long term laminate predictions. Comparisons are made between theory and experiment.

Brinson, H. F.↗

NASA NTRS1983

A model-based investigation of manipulator characteristics and pilot/vehicle performance

Hess (1978, 1981) has introduced and discussed a structural model of the human pilot in which proprioceptive feedback plays a fundamental role in determining pilot equalization characteristics. It is pointed out that, on account of the feedback structure, this model may provide more insight into the effects of certain manipulator characteristics upon pilot equalization than would other modeling approaches. The model is briefly discussed, and an outline is presented concerning some of the implications of the model structure regarding the manipulator characteristics. Attention is given to some specific empirical examples of manipulator effects involving glide slope tracking in STOL aircraft, taking into account an employment of the model as a theoretical framework.

Hess, R. A.↗

NASA NTRS1985

Shock tube study of the fuel structure effects on the chemical kinetic mechanisms responsible for soot formation, part 2

Soot formation in oxidation of allene, 1,3-butadiene, vinylacetylene and chlorobenzene and in pyrolysis of ethylene, vinylacetylene, 1-butene, chlorobenzene, acetylen-hydrogen, benzene-acetylene, benzene-butadiene and chlorobenzene-acetylene argon-diluted mixtures was studied behind reflected shock waves. The results are rationalized within the framework of the conceptual models. It is shown that vinylacetylene is much less sooty than allene, which indicates that conjugation by itself is not a sufficient factor for determining the sooting tendency of a molecule. Structural reactivity in the context of the chemical kinetics is the dominant factor in soot formation. Detailed chemical kinetic modeling of soot formation in pyrolysis of acetylene is reported. The main mass growth was found to proceed through a single dominant route composed of conventional radical reactions. The practically irreversible formation reactions of the fused polycyclic aromatics and the overshoot by hydrogen atom over its equilibrium concentration are the g-driving kinetic forces for soot formation.

Frenklach, M.↗

NASA NTRS1983

Experimental philosophy leading to a small scale digital data base of the conterminous United States for designing experiments with remotely sensed data

Research using satellite remotely sensed data, even within any single scientific discipline, often lacked a unifying principle or strategy with which to plan or integrate studies conducted over an area so large that exhaustive examination is infeasible, e.g., the U.S.A. However, such a series of studies would seem to be at the heart of what makes satellite remote sensing unique, that is the ability to select for study from among remotely sensed data sets distributed widely over the U.S., over time, where the resources do not exist to examine all of them. Using this philosophical underpinning and the concept of a unifying principle, an operational procedure for developing a sampling strategy and formal testable hypotheses was constructed. The procedure is applicable across disciplines, when the investigator restates the research question in symbolic form, i.e., quantifies it. The procedure is set within the statistical framework of general linear models. The dependent variable is any arbitrary function of remotely sensed data and the independent variables are values or levels of factors which represent regional climatic conditions and/or properties of the Earth's surface. These factors are operationally defined as maps from the U.S. National Atlas (U.S.G.S., 1970). Eighty-five maps from the National Atlas, representing climatic and surface attributes, were automated by point counting at an effective resolution of one observation every 17.6 km (11 miles) yielding 22,505 observations per map. The maps were registered to one another in a two step procedure producing a coarse, then fine scale registration. After registration, the maps were iteratively checked for errors using manual and automated procedures. The error free maps were annotated with identification and legend information and then stored as card images, one map to a file. A sampling design will be accomplished through a regionalization analysis of the National Atlas data base (presently being conducted). From this analysis a map of homogeneous regions of the U.S.A. will be created and samples (LANDSAT scenes) assigned by region.

Labovitz, M. L.↗

NASA NTRS1984

The E ring of Saturn and satellite Enceladus

Photographic imagery from Pioneer and Voyager flyby satellites has been used to study the microphysical properties of Saturn's outermost E-ring, and to determine the physical relationship between the E-ring and the satellite Enceladus. The optical and infrared characteristics of the E-ring are explained in terms of Mie scattering of ice spheres with an effective diameter of 2 to 2.25 microns and an effective variance of 0.1 to 1.5. It is suggested that the E-ring is continuously replenished by volcanic eruptions on Enceladus, and recent tectonic evidence is cited in support of this hypothesis. A number of similarities in the relationship between the E-ring and Enceladus and Io and its torus are discussed, within the framework of a general model of outer solar system volcanism and planetary ring interaction.

Pang, K. D.↗

NASA NTRS1984

Results from the transition region camera

Three series of high resolution ultra-violet pictures of the sun have been obtained during the three flights of rocket experiment T.R.C. Transition Region Camera) which took place on 3 July 1979, 23 September 1980 and 13 July 1982. These pictures reveal many structures in Ly alpha and ultraviolet continua at 160 nm and 220 nm. The scientific objectives, instrumentation, flight conditions and campaigns of simultaneous observations are described. The contribution of T.R.C. to solar physics is discussed in the framework of chromospheric multicomponent models, magnetic flux tubes, local heating and periodic structures in the chromosphere.

Foing, B. H.↗

NASA NTRS1986

Input impedance of a probe-fed circular microstrip antenna with thick substrate

A method of computing the input impedance for the probe fed circular microstrip antenna with thick dielectric substrate is presented. Utilizing the framework of the cavity model, the fields under the microstrip patch are expanded in a set of modes satisfying the boundary conditions on the eccentrically located probe, as well as on the cavity magnetic wall. A mode-matching technique is used to solve for the electric field at the junction between the cavity and the coaxial feed cable. The reflection coefficient of the transverse electromagnetic (TEM) mode incident in the coaxial cable is determined, from which the input impedance of the antenna is computed. Measured data are presented to verify the theoretical calculations. Results of the computation of various losses for the circular printed antenna as a function of substrate thickness are also included.

Davidovitz, M.↗

NASA NTRS1987

Six reasons why thermospheric measurements and models disagree

The differences between thermospheric measurements and models are discussed. Sometimes the model is in error and at other times the measurements are, but it also is possible for both to be correct, yet have the comparison result in an apparent disagreement. These reasons are collected for disagreement, and, whenever possible, methods of reducing or eliminating them are suggested. The six causes of disagreement discussed are: actual errors caused by the limited knowledge of gas-surface interactions and by in-track winds; limitations of the thermospheric general circulation models due to incomplete knowledge of the energy sources and sinks as well as incompleteness of the parameterization which must be employed; and limitations imposed on the empirical models by the conceptual framework and the transient waves.

Moe, Kenneth↗

NASA NTRS1987

On the generation of field-aligned plasma flow at the boundary of the plasma sheet

A possible cause of the large plasma flow velocities parallel to the magnetic field (which were observed in spacecraft experiments) near the boundary of the plasma sheet in the earth's magnetotail is considered in the framework of a magnetohydrodynamic model. It is shown for steady-state configurations that high parallel flow velocities can be expected to exist on field lines connecting to a region of weak magnetic field. The physical mechanism causing large values of the parallel velocity component can be visualized as a strong imbalance of perpendicular mass flux into and out of magnetic flux tubes passing through regions where the magnetic field is weak and inhomogeneous. The value of the parallel velocity component is evaluated, and it is found that it can substantially exceed the perpendicular velocity (by as much as a factor of 40). The results are applied to the earth's magnetotail; it is found that this mechanism is able to explain the parallel flow velocities near the boundary of the plasma sheet in the range of several hundreds of km/s.

Schindler, K.↗

NASA NTRS1988

Object oriented studies into artificial space debris

A prototype simulation is being developed under contract to the Royal Aerospace Establishment (RAE), Farnborough, England, to assist in the discrimination of artificial space objects/debris. The methodology undertaken has been to link Object Oriented programming, intelligent knowledge based system (IKBS) techniques and advanced computer technology with numeric analysis to provide a graphical, symbolic simulation. The objective is to provide an additional layer of understanding on top of conventional classification methods. Use is being made of object and rule based knowledge representation, multiple reasoning, truth maintenance and uncertainty. Software tools being used include Knowledge Engineering Environment (KEE) and SymTactics for knowledge representation. Hooks are being developed within the SymTactics framework to incorporate mathematical models describing orbital motion and fragmentation. Penetration and structural analysis can also be incorporated. SymTactics is an Object Oriented discrete event simulation tool built as a domain specific extension to the KEE environment. The tool provides facilities for building, debugging and monitoring dynamic (military) simulations.

Adamson, J. M.↗

NASA NTRS1991

Expert decision-making strategies

A recognition-primed decisions (RPD) model is employed as a framework to investigate crew decision-making processes. The quality of information transfer, a critical component of the team RPD model and an indicator of the team's 'collective consciouness', is measured and analyzed with repect to crew performance. As indicated by the RPD model, timing and patterns of information search transfer were expected to reflect extensive and continual situation assessment, and serial evaluation of alternative states of the world or decision response options.

Mosier, Kathleen L.↗

NASA NTRS1992

An integrated development of the equations of motion for elastic hypersonic flight vehicles

An integrated, consistent analytical framework is developed for modeling the dynamics of elastic hypersonic flight vehicles. A Lagrangian approach is used in order to capture the dynamics of rigid-body motion, elastic deformation, fluid flow, rotating machinery, wind, and a spherical rotating earth model, and to account for their interactions with each other. A vector form of the force, moment and elastic-deformation equations is developed from Lagrange's equation; a useable scalar form of these equations is also presented. The appropriate kinematic equations are developed, and are presented in a useable form. A preliminary study of the significance of selected terms in the equations of motion is conducted. Using generic data for a single-stage-to-orbit vehicle, it was found that the Coriolis force can reach values of up to 6 percent of the vehicle weight, and that the forces and moments attributable to fluid-flow terms can be significant.

Bilimoria, Karl D.↗

NASA NTRS1992

ROSAT all-sky survey on the Einstein EMSS sample

The cosmological evolution and the luminosity function (XLF) of X ray selected Active Galactic Nuclei (AGN's) are discussed. The sample used is extracted from the Einstein Observatory Extended Medium Sensitivity Surveys (EMSS) and consists of more than 420 objects. Preliminary results from the ROSAT All-Sky Survey data confirm the correctness of the optical identification of the EMSS sources, thus giving confidence to the results obtained from the analysis of the AGN's sample. The XLF observed at different redshifts (up to z approx. 2) gives direct evidence of cosmological evolution. Data have been analyzed within the framework of luminosity evolution models and the two most common evolutionary forms, L sub x(Z) = L sub x(0) x e(sup Cr) and L sub x(Z) = L sub x(0) x (1 + z)(exp C), have been considered. Luminosity dependent evolution is required if the evolution function has the exponential form, whereas the simpler pure luminosity evolution model is still acceptable if the evolution function has the power law form. Using the whole sample of objects the number-counts and the de-evolved (z = 0) XLF have been derived. A comparison of the EMSS data with preliminary ROSAT results presented at this meeting indicates an overall agreement.

Maccacaro, Tomasso↗

NASA NTRS1992

The evolution of AGN's at x ray wavelengths

The cosmological evolution and the Luminosity Function (LF) of x-ray selected Active Galactic Nuclei (AGN) are discussed. The sample used is extracted from the Einstein Observatory Extended Medium Sensitivity Survey (EMSS) and consists of more than 420 objects. Preliminary results from the Rosat all sky survey data confirm the correctness of the optical identification of the EMSS sources, thus giving confidence to the results obtained from the analysis of the AGN sample. The XLF observed at different redshifts gives direct evidence of cosmological evolution. Data were analyzed within the framework of luminosity evolution models and the two most common evolutionary forms were considered. Luminosity dependent evolution is required if the evolution function has the exponential form, whereas the simpler pure luminosity evolution model is still acceptable if the evolution function has the power law form. Using the whole sample of objects the number counts and the devolved XLF were derived. A comparison of the EMSS Data with preliminary Rosat results indicates an overall agreement.

Maccacaro, Tommaso↗

NASA NTRS1993

An autonomous satellite architecture integrating deliberative reasoning and behavioural intelligence

This paper describes a method for the design of autonomous spacecraft, based upon behavioral approaches to intelligent robotics. First, a number of previous spacecraft automation projects are reviewed. A methodology for the design of autonomous spacecraft is then presented, drawing upon both the European Space Agency technological center (ESTEC) automation and robotics methodology and the subsumption architecture for autonomous robots. A layered competency model for autonomous orbital spacecraft is proposed. A simple example of low level competencies and their interaction is presented in order to illustrate the methodology. Finally, the general principles adopted for the control hardware design of the AUSTRALIS-1 spacecraft are described. This system will provide an orbital experimental platform for spacecraft autonomy studies, supporting the exploration of different logical control models, different computational metaphors within the behavioral control framework, and different mappings from the logical control model to its physical implementation.

Lindley, Craig A.↗