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NASA NTRS1988

Clustering correlations and limits on cosmological gravitational waves

A cosmological background of gravitational waves induces angular deviations in the propagation of light traversing it. All observed astrophysical sources might therefore have varying apparent positions, with the time dependence set by the wave period. Wavelengths greater than a kiloparsec are examined, so the positions are frozen but in general correlated. Comparison with observed galaxy-galaxy n-point correlation functions provide a spectrum-independent limit on the energy density of gravitational waves with wavelengths between a few tens of kiloparsecs and a few hundred megaparsecs of Omega(GW) less than 0.001.

Linder, Eric V.↗

NASA NTRS1988

Downstream energetic proton and alpha particles during quasi-parallel interplanetary shock events

This paper considers the energetic particle populations in the downstream region of three quasi-parallel interplanetary shock events, which was explored using the ISEE 3 Ultra Low Energy Charge Analyzer sensor, which unambiguously identifies protons and alpha particles using the electrostatic deflection versus residual energy technique. The downstream particles were found to exhibit anisotropies due largely to convection in the solar wind. The spectral indices of the proton and the alpha-particle distribution functions were found to be remarkably constant during the downstream period, being generally insensitive to changes in particle flux levels, magnetic field direction, and solar wind densities. In two of the three events, the proton and the alpha spectra were the same throughout the entire downstream period, supporting the prediction of diffusive shock acceleration theory.

Tan, L. C.↗

NASA NTRS1988

A new algorithm for modeling friction in dynamic mechanical systems

A method of modeling friction forces that impede the motion of parts of dynamic mechanical systems is described. Conventional methods in which the friction effect is assumed a constant force, or torque, in a direction opposite to the relative motion, are applicable only to those cases where applied forces are large in comparison to the friction, and where there is little interest in system behavior close to the times of transitions through zero velocity. An algorithm is described that provides accurate determination of friction forces over a wide range of applied force and velocity conditions. The method avoids the simulation errors resulting from a finite integration interval used in connection with a conventional friction model, as is the case in many digital computer-based simulations. The algorithm incorporates a predictive calculation based on initial conditions of motion, externally applied forces, inertia, and integration step size. The predictive calculation in connection with an external integration process provides an accurate determination of both static and Coulomb friction forces and resulting motions in dynamic simulations. Accuracy of the results is improved over that obtained with conventional methods and a relatively large integration step size is permitted. A function block for incorporation in a specific simulation program is described. The general form of the algorithm facilitates implementation with various programming languages such as FORTRAN or C, as well as with other simulation programs.

Hill, R. E.↗

NASA NTRS1988

On the long-tail solar wind electron velocity distribution

The role of the log-normal distribution in the description of the high-energy tail of the electron velocity distribution in the solar wind plasma is examined. Specifically, it is shown that the core-halo solar wind distribution function can be understood in terms of a simple phenomenological model of general applicability in which the core has a Maxwellian or normal distribution and the halo a log-normal distribution. In the presence of structures in the interplanetary medium capable of interacting with the electrons, the model predicts a transition at the highest velocities to a secondary halo distribution.

Shlesinger, Michael F.↗

NASA NTRS1989

Cloud-generated radiative heating and its generation of available potential energy

The generation of zonal available potential energy (APE) by cloud radiative heating is discussed. The APE concept was mathematically formulated by Lorenz (1955) as a measure of the maximum amount of total potential energy that is available for conversion by adiabatic processes to kinetic energy. The rate of change of APE is the rate of the generation of APE minus the rate of conversion between potential and kinetic energy. By radiative transfer calculations, a mean cloud-generated radiative heating for a well defined set of cloud classes is derived as a function of cloud optical thickness. The formulation is suitable for using a general cloud parameter data set and has the advantage of taking into account nonlinearities between the microphysical and macrophysical cloud properties and the related radiation field.

Stuhlmann, R.↗

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 NTRS1990

Computing maximum tracking error due to payload dynamics

The determination of maximum endpoint tracking error due to uncompensated inertial payload dynamics is investigated. The problem is formulated on the basis of well-known kinetic and kinematic relationships with constraints on maximum joint positions and velocities as well as the generalized force/speed constraint relationship for each actuator. An endpoint tracking error objective function is formed, and numerical optimization is used to determine the maximum. An example computation is presented to show the tracking error under progressively increasing payload using a PUMA 560 manipulator with its first three joints in motion.

Kelkar, Atul G.↗

NASA NTRS1991

Far-ultraviolet mapping of the Cygnus Loop with the Voyager 2 Ultraviolet Spectrometer

FUV maps of the Cygnus Loop made using spectroscopic data from the Voyager 2 Ultraviolet Spectrometer are presented. Emission line features at about 980 and about 1035 A dominate the 500-1700 A spectra of the Cygnus Loop as observed with Voyager. Maps were generated in the light of these two features. The 980 and 1035 A maps are compared with X-ray and optical images of the Cygnus Loop that have been sampled in the same manner. From this comparison it is clear that the 980 A feature arises mainly from regions of bright optical emission, whereas the 1035 A emission more closely resembles the X-ray emission. This general impression can be confirmed by inspection of the spectra as a function of position. Spectra extracted from positions corresponding to the primary shock front show the 1035 A feature to be relatively strong, while the 980 A feature is brighter when substantial optical emission is present within the aperture.

Blair, William P.↗

NASA NTRS1991

The correlation function of galaxy ellipticities produced by gravitational lensing

The correlation of galaxy ellipticities produced by gravitational lensing is calculated as a function of the power spectrum of density fluctuations in the universe by generalizing an analytical method developed by Gunn (1967). The method is applied to a model where identical objects with spherically symmetric density profiles are randomly laid down in space, and to the cold dark matter model. The possibility of detecting this correlation is discussed. Although an ellipticity correlation can also be caused by an intrinsic alignment of the axes of galaxies belonging to a cluster or a supercluster, a method is suggested by which one type of correlation can be distinguished from another. The advantage of this ellipticity correlation is that it is one of the few astronomical observations that can directly probe large-scale mass fluctuations in the universe.

Miralda-Escude, Jordi↗

NASA NTRS1991

Lessons learned in control center technologies and non-technologies

Information is given in viewgraph form on the Solar Mesosphere Explorer (SME) Control Center and the Oculometer and Automated Space Interface System (OASIS). Topics covered include SME mission operations functions; technical and non-technical features of the SME control center; general tasks and objects within the Space Station Freedom (SSF) ground system nodes; OASIS-Real Time for the control and monitoring of of space systems and subsystems; and OASIS planning, scheduling, and PC architecture.

Hansen, Elaine R.↗

NASA NTRS1991

The role of the Consultative Committee on International Radio (CCIR) in time and frequency

The Consultative Committee on International Radio (CCIR) is a technical advisory group that, within the International Telecommunications Union (ITU), provides formal recommendations, technical advice, and technical information related to the allocation and use of the radio spectrum. The CCIR does its work through a number of separate study groups, each of which deals primarily with one or more radio based services recognized by the ITU. One of these, Study Group 7, is called 'Science Services' and deals with, among other things, time and frequency services, and related topics. This part of CCIR is probably best known for its development and implementation of the UTC time system in 1972. The U.S. National Administration develops proposed recommendations and provides other technical input to the CCIR through an organization of U.S. Study Groups that parallel those functioning internationally. Both the private and government sectors participate actively under the general oversight of the U.S. State Department and its U.S. CCIR National Committee. Current and projected future activities of U.S. and international Study Group 7 are described, including some examples of current recommendations, handbooks, and other documentation that might be useful for working with time and frequency applications.

Roger E. Beehler↗

NASA NTRS1990

Space Station Freedom biomedical monitoring and countermeasures: Biomedical facility hardware catalog

This hardware catalog covers that hardware proposed under the Biomedical Monitoring and Countermeasures Development Program supported by the Johnson Space Center. The hardware items are listed separately by item, and are in alphabetical order. Each hardware item specification consists of four pages. The first page describes background information with an illustration, definition and a history/design status. The second page identifies the general specifications, performance, rack interface requirements, problems, issues, concerns, physical description, and functional description. The level of hardware design reliability is also identified under the maintainability and reliability category. The third page specifies the mechanical design guidelines and assumptions. Described are the material types and weights, modules, and construction methods. Also described is an estimation of percentage of construction which utilizes a particular method, and the percentage of required new mechanical design is documented. The fourth page analyzes the electronics, the scope of design effort, and the software requirements. Electronics are described by percentages of component types and new design. The design effort, as well as, the software requirements are identified and categorized.

Source record↗

NASA NTRS1993

Advanced Transport Operating System (ATOPS) utility library software description

The individual software processes used in the flight computers on-board the Advanced Transport Operating System (ATOPS) aircraft have many common functional elements. A library of commonly used software modules was created for general uses among the processes. The library includes modules for mathematical computations, data formatting, system database interfacing, and condition handling. The modules available in the library and their associated calling requirements are described.

Clinedinst, Winston C.↗

NASA NTRS1993

A Hubble Space Telescope planetary camera view of giant H II regions - The Wolf-Rayet content of NGC 595 and NGC 604 in M33

We present images of NGC 595 and NGC 604, the most massive giant H II regions in M33, obtained with the Planetary Camera aboard the HST in order to study their WR population. Fourteen WR and/or Of candidates are detected in NGC 604, and eleven in NGC 595. All previously claimed 'superluminous' WR stars are found to be tight (diameter less than 3 pc) stellar aggregates containing one (or sometimes more) normal WR star. As suspected from ground-based data, the WR/O number ratio is significantly higher in NGC 595 (about 0.3) than in NGC 604 (about 0.1). The WR stars may be major contributors to the output of mechanical power and energy into the interstellar medium in both clusters. Over the observable initial mass range, the initial mass functions (IMFs) have similar slopes. These IMFs are somewhat flatter than those generally derived for massive stars in the Galaxy or the Magellanic Clouds.

Drissen, Laurent↗

NASA NTRS1923

Wind tunnel tests of five strut sections in yaw

In the first series of wind tunnel tests, the drag and cross wing force of all the struts were measured at a wind speed of 30 mph and at angles of yaw from 0 degrees to 20 degrees. To determine the magnitude of the VL effect, each strut was tested at zero yaw and at a series of speeds ranging from 15 to 38 mph. Although designed as fairings for cables, part of these sections gave such high crosswind forces that they seemed to have possibilities as airfoils. Therefore, the lift (identical with the crosswind force) and drag coefficients were recalculated for four sections on the basis of broadside area to make them comparable with wing coefficients. The general conclusion that the best fineness ratio for a strut is a function of the Reynolds number, decreasing steadily as that quality increases, has of course been reached many times, both by theory and experiment. It was confirmed here once more, and the effect of form on sensitiveness to VL is also strikingly shown. It seems probable that this effect of form is largely due to interaction between the nose and tail, and to the influence which the form of the nose exerts over the whole flow around the strut.

PROPELLERS, METAL↗

NASA NTRS1937

Cooling of Airplane Engines at Low Air Speeds

Report presents the results of a comprehensive experimental study carried out at full scale in the NACA 20-foot wind tunnel, the general purpose of which is to furnish information in regard to the functioning of the power plant and propeller unit under different conditions. This report deals particularly with the problem of the cooling of an airplane engines on the ground. The influence of different nose forms, skirts, flaps, propellers, spinners, and special blowers has been investigated.

Theodorsen, Theodore↗

NASA NTRS1995

The space-time solution element method: A new numerical approach for the Navier-Stokes equations

This paper is one of a series of papers describing the development of a new numerical method for the Navier-Stokes equations. Unlike conventional numerical methods, the current method concentrates on the discrete simulation of both the integral and differential forms of the Navier-Stokes equations. Conservation of mass, momentum, and energy in space-time is explicitly provided for through a rigorous enforcement of both the integral and differential forms of the governing conservation laws. Using local polynomial expansions to represent the discrete primitive variables on each cell, fluxes at cell interfaces are evaluated and balanced using exact functional expressions. No interpolation or flux limiters are required. Because of the generality of the current method, it applies equally to the steady and unsteady Navier-Stokes equations. In this paper, we generalize and extend the authors' 2-D, steady state implicit scheme. A general closure methodology is presented so that all terms up through a given order in the local expansions may be retained. The scheme is also extended to nonorthogonal Cartesian grids. Numerous flow fields are computed and results are compared with known solutions. The high accuracy of the scheme is demonstrated through its ability to accurately resolve developing boundary layers on coarse grids. Finally, we discuss applications of the current method to the unsteady Navier-Stokes equations.

Scott, James R.↗

NASA NTRS1995

Bringing the cross-correlation method up to date

The cross-correlation (XC) method of Tonry & Davis (1979, AJ, 84, 1511) is generalized to arbitrary parametrized line profiles. In the new algorithm the correlation function itself, rather than the observed galaxy spectrum, is fitted by the model line profile: this removes much of the complication in the error analysis caused by template mismatch. Like the Fourier correlation quotient (FCQ) method of Bender (1990, A&A, 229, 441), the inferred line profiles are, up to a normalization constant, independent of template mismatch as long as there are no blended lines. The standard reduced chi(exp 2) is a good measure of the fit of the inferred velocity distribution, largely decoupled from the fit of the spectral template. The updated XC method performs as well as other recently developed methods, with the added virtue of conceptual simplicity.

Statler, Thomas↗