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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Phase Two of the Array Automated Assembly Task for the Low Cost Solar Array Project

Various top contact metal systems were studied. Only Ti Pd Cu approaches baseline (Ti Pd Ag) quality, but this system shows a lack of long term stability. Aluminum back surface field structures were fabricated and thicknesses of p superscript + material of up to 7.0 microns were achieved with open circuit voltages of 0.59V. A general purpose ultrasonic welder was purchased and tests using various metal foils are under way. During fabrication of the demonstration module, several cells became cracked. Due to redundancy of interconnections, the module was not open circuited but the efficiency was reduced to 8.8%. The broken cell was interconnected with a strap across the back and the efficiency was increased to 11.5%. A cost analysis was made and the results indicate a selling price of $0.56/watt peak (in 1986 with 1975 dollars).

Campbell, R. B.↗
NASA NTRS1981

Stability analysis of automobile driver steering control

In steering an automobile, the driver must basically control the direction of the car's trajectory (heading angle) and the lateral deviation of the car relative to a delineated pathway. A previously published linear control model of driver steering behavior which is analyzed from a stability point of view is considered. A simple approximate expression for a stability parameter, phase margin, is derived in terms of various driver and vehicle control parameters, and boundaries for stability are discussed. A field test study is reviewed that includes the measurement of driver steering control parameters. Phase margins derived for a range of vehicle characteristics are found to be generally consistent with known adaptive properties of the human operator. The implications of these results are discussed in terms of driver adaptive behavior.

Allen, R. W.↗
NASA NTRS1983

Efficient linear and nonlinear heat conduction with a quadrilateral element

A method is presented for performing efficient and stable finite element calculations of heat conduction with quadrilaterals using one-point quadrature. The stability in space is obtained by using a stabilization matrix which is orthogonal to all linear fields and its magnitude is determined by a stabilization parameter. It is shown that the accuracy is almost independent of the value of the stabilization parameter over a wide range of values; in fact, the values 3, 2, and 1 for the normalized stabilization parameter lead to the 5-point, 9-point finite difference, and fully integrated finite element operators, respectively, for rectangular meshes and have identical rates of convergence in the L2 norm. Eigenvalues of the element matrices, which are needed for stability limits, are also given. Numerical applications are used to show that the method yields accurate solutions with large increases in efficiency, particularly in nonlinear problems.

Liu, W. K.↗
NASA NTRS1984

Efficient linear and nonlinear heat conduction with a quadrilateral element

A method is presented for performing efficient and stable finite element calculations of heat conduction with quadrilaterals using one-point quadrature. The stability in space is obtained by using a stabilization matrix which is orthogonal to all linear fields and its magnitude is determined by a stabilization parameter. It is shown that the accuracy is almost independent of the value of the stabilization parameter over a wide range of values; in fact, the values 3, 2 and 1 for the normalized stabilization parameter lead to the 5-point finite difference, 9-point finite difference and fully integrated finite element operators, respectively, for rectangular meshes; numerical experiments reported here show that the three have identical rates of convergence in the L2 norm. Eigenvalues of the element matrices, which are needed for stability limits, are also given. Numerical applications are used to show that the method yields accurate solutions with large increases in efficiency, particularly in nonlinear problems.

Liu, W. K.↗
NASA NTRS1984

Cryogenic telescope on the Infrared Astronomical Satellite (IRAS)

The Infrared Astronomical Satellite (IRAS) has completed an unbiased all-sky survey at wavelengths from 10 to 100 microns. The design and performance of the focal plane array is described with emphasis on in-orbit measurements of the sensitivity and stability. In the four broad spectral bands centered at 12, 25, 60, and 100 microns, the system noise equivalent flux density (NEFD) values are in Jy/(Square root of Hz), 0.03, 0.025, 0.046, and 0.21, respectively (Jansky = 10 to the -26th W/sq m/Hz). For point sources, a single scan at the survey rate of 3.8 arcmin/s yields limiting flux densities at the 3-sigma confidence level of 0.36, 0.30, 0.39, and 1.2 Jy. The dc stability of the junction field effect transistor (JFET) amplifiers and the excellent off-axis rejection of the telescope permit total flux measurements of extended infrared emission at levels below 6,000,000 Jy/sr. Response of the extrinsic silicon and germanium photo-detectors to ionizing radiation is described.

Low, F. J.↗
NASA NTRS1986

Determining Calibration Constants for Attitude Measurements

Algorithm based on method of least squares determines calibration constants of seismic instruments for precise attitude measurements. Algorithm programed and run successfully on commercially available desk-top computer. Simplifies determinations of accelerometer calibration constants, and used in field to verify accelerometer stability.

Tcheng, P.↗
NASA NTRS1984

Thermosolutal convection during directional solidification

During solidification of a binary alloy at constant velocity vertically upward, thermosolutal convection can occur if the solute rejected at the crystal-melt interface decreases the density of the melt. We assume that the crystal-melt interface remains planar and that the flow field is periodic in the horizontal direction. The time-dependent nonlinear differential equations for fluid flow, concentration, and temperature are solved numerically in two spatial dimensions for small Prandtl numbers and moderately large Schmidt numbers. For slow solidification velocities, the thermal field has an important stabilizing influence: near the onset of instability the flow is confined to the vicinity of the crystal-melt interface. Further, for slow velocities, as the concentration increases, the horizontal wavelength of the flow decreases rapidly - a phenomenon also indicated by linear stability analysis. The lateral inhomogeneity in solute concentration due to convection is obtained from the calculations. For a narrow range of solutal Rayleigh numbers and wavelengths, the flow is periodic in time.

Mcfadden, G. B.↗
NASA NTRS1989

MU radar observation of a mesospheric gravity wave breaking caused by convective instability

In recent measurements of mesospheric winds with the MU radar at Shigaraki (34.9 N, 136.1 E), Japan, a couple of wind velocity data was obtained showing that a monochromatic inertia-gravity wave was propagating vertically in the mesosphere. The data show that the velocity amplitude of the wave did not increase exponentially above a height and further show that the wave form had broken down at a level. Evaluating the changes of the atmospheric stability in the wave field from the measured wind data and from the estimated wave parameters, the breakdown of the wave was shown to be connected with the occurrence of convective instability in the wave field.

Muraoka, Y.↗
NASA NTRS1990

Free flow cell electrophoresis using zwitterionic buffer

Studies of a zwitterionic buffer formulated for cell electrophoresis were done using the McDonnell-Douglas Continuous Flow Electrophoresis System. Standard buffers were analyzed for their stability in the electrical field and the results showed that both buffers tested were inherently unstable. Further, titration studies showed that the standards buffers buffered poorly at the pH employed for electrophoresis. The zwitterionic buffer buffered well at its nominal pH and was shown to be stable in the electrical field. Comparative studies of the buffer with standard cell separation buffers using formalin fixed rabbit and goose red blood cells showed that the zwitterionic buffer gave better resolution of the fixed cells. Studies with viable hybridoma cells showed that buffer Q supported cell viability equal to Hank's Balanced Salt Solution and that hybridoma cells in different stages of the growth cycle demonstrated reproducible differences in electrophoretic mobility.

Rodkey, R. Scott↗
NASA NTRS1993

High speed transition prediction

The main objective of this work period was to develop, maintain and exercise state-of-the-art methods for transition prediction in supersonic flow fields. Basic state and stability codes, acquired during the last work period, were exercised and applied to calculate the properties of various flowfields. The development of a code for the prediction of transition location using a currently novel method (the PSE or Parabolized Stability Equation method), initiated during the last work period and continued during the present work period, was cancelled at mid-year for budgetary reasons. Other activities during this period included the presentation of a paper at the APS meeting in Tallahassee, Florida entitled 'Stability of Two-Dimensional Compressible Boundary Layers', as well as the initiation of a paper co-authored with H. Reed of the Arizona State University entitled 'Stability of Boundary Layers'.

Gasperas, Gediminis↗
NASA NTRS1994

Triple flames and flame stabilization

It is now well established that when turbulent jet flames are lifted, combustion begins, i.e., the flame is stabilized, at an axial station where the fuel and air are partially premixed. One might expect, therefore, that the beginning of the combustion zone would be a triple flame. Such flames have been described; however, other experiments provide data that are difficult to reconcile with the presence of triple flames. In particular, laser images of CH and OH, marking combustion zones, do not exhibit shapes typical of triple flames, and, more significantly, the lifted flame appears to have a propagation speed that is an order of magnitude higher than the laminar flame speed. The speed of triple flames studied thus far exceeds the laminar value by a factor less than two. The objective of the present task is the resolution of the apparent conflict between the experiments and the triple flame characteristics, and the clarification of the mechanisms controlling flame stability. Being investigated are the resolution achieved in the experiments, the flow field in the neighborhood of the stabilization point, propagation speeds of triple flames, laboratory flame unsteadiness, and the importance of flame ignition limits in the calculation of triple flames that resemble lifted flames.

Broadwell, James E.↗
NASA NTRS1996

Simulation and Modeling of the Elliptic Streamline Flow

Direct numerical simulation (DNS) was used to study homogeneous turbulence with a mean flow having elliptic streamlines. This flow combines the effects of rotation and strain on the turbulence. There are many important reasons for studying the elliptic streamline flow. This flow contains the effects of both rotation and strain and is therefore similar to the mean flow in a vortex strained in the plane perpendicular to its axis. Such flows provide insight into the fundamental vortical interactions within turbulence. A strained vortex also occurs in airplane wakes, in which each wingtip vortex induces a strain field on the other. The strain field can affect the stability of these vortices and thereby their turbulent structure downstream. The ability to understand and predict the turbulent structure of the vortices is important to the wake hazard problem which is of major concern for the safety of commercial aircraft.

Blaisdell, Gregory A.↗
NASA NTRS1996

Determination of Stability and Translation in a Boundary Layer

Reducing the infinite degrees of freedom inherent in fluid motion into a manageable number of modes to analyze fluid motion is presented. The concepts behind the center manifold technique are used. Study of the Blasius boundary layer and a precise description of stability within the flow field are discussed.

Crepeau, John↗
NASA NTRS1997

The SeaWiFS Quality Monitor: A Portable Field Calibration Light Source

A portable and stable source, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Quality Monitor, has been developed for use as a field instrument. The source can be used with either radiance- or irradiance-measuring sensors to transfer the laboratory calibration to the field so that the stability of the sensors can be monitored during the experiment. Temperature-controlled silicon photodiodes with colored glass filters are used to monitor the stability of the SeaWiFS Quality Monitor.

Shaw, Ping-Shine↗
NASA NTRS2001

Miniature Free-Flying Magnetometer Utilizing System-On-A-Chip Technology

Four Free-Flying Magnetometers (FFMs), developed at the Jet Propulsion Laboratory (JPL) for the Enstrophy mission, were successfully deployed from the payload of a sounding rocket launched from Poker Flats, Alaska on February 11, 1999. The FFMs functioned successfully by synchronously measuring the vector magnetic field at 4 points separate from the payload and at relative distances up to 3 km, and communicated their data, in bursts, to the ground. This is the first time synchronized in-situ multipoint measurements of the Earth's magnetic field utilizing miniature spin-stabilized "sensorcraft" have been performed. The data they provided have enabled, for the first time, the direct measure of field-aligned current density and are enabling new science by determining the fine-scale structure of the currents in the Earth's ionosphere involved in the production of aurora. These proof-of-concept "hockey puck" (80 mm diameter, 38 mm height, 250 gram mass) FFMs were built using off-the-shelf commercial, industrial, and military grade surface-mount electronic components. Radiation-hard electronics was not required for the Enstrophy mission's short sub-orbital flight. The successful design, implementation, and flight demonstration of this 1st generation FFM design has provided a solid base for further development of a 2nd generation FFM design for planetary science applications. A reliable ultra-miniature radiation-hard 2nd-generation FFM utilizing System-On-A-Chip (SOAC) technologies is proposed. This design would be targeted for long-term planetary missions to investigate magnetospheric field configurations in regions having small-scale structure and to separate spatial and temporal variations. A fleet of short-lived (expendable) FFMs would be deployed into a targeted region to gather multiprobe vector magnetic field data. The FFMs would be ejected from a parent spacecraft at a speed of a few m/sec and would cover spatial volumes of order tens of kilometers for times of order one hour. The parent spacecraft would carry a sufficient number of FFMs for multiple deployments. Additional information is contained in the original extended abstract.

Eyre, F. B.↗
NASA NTRS2001

EIT and SXT Observations of a Quiet Region Filament Ejection: First Eruption, Then Reconnection

We observe a slow-onset quiet-region filament eruption with the EUV Imaging Telescope (EIT) on SOHO, and the Soft X-ray Telescope (SXT) on Yohkoh. This event occurred on 1999 April 18, and was likely the origin of a coronal mass ejection (CME) detected by SOHO at 08:30 UT on that day. In EIT, one-half of the filament shows two stages of evolution: Stage I is a slow, roughly constant upward movement at approx. 1 km per second lasting approximately 6.5 hours, and Stage 2 is a rapid upward eruption at approximately 16 kilometers per second occurring just before the filament disappears into interplanetary space. The other half of the filament shows little motion along the line-of-sight during the time of Stage 1, but erupts along with the rest of the filament during Stage 2. There is no obvious emission from the filament in SXT until Stage 2; at that time an arcade of EUV and soft X-ray loops forms first at the central location of the filament, and then expands outward along the length of the filament channel. A plot of EUV intensity versus time of the central portion of the filament (where the postflare loops initially form) shows a flat profile during Stage 1, and a rapid upturn after the start of Stage 2. This lightcurve is delayed from what would be expected if "tether-cutting" reconnection in the core of the erupting region were responsible for the initiation of the eruption. Rather, these observations suggest that a loss of stability of the magnetic field holding the filament initiates the eruption, with reconnection in the core region occurring only as a byproduct.

Sterling, Alphonse C.↗
NASA NTRS2001

EIT And SXT Observations of a Quiet-Region Filament Ejection: First Eruption, Then Reconnection

We observe a slow-onset quiet-region filament eruption with the Extreme Ultraviolet Imaging Telescope (EIT) on the Solar Heliospheric Observatory (SOHO) and the Soft X-ray Telescope (SXT) on Yohkoh. This event occurred on 1999 April 18 and was likely the origin of a coronal mass ejection detected by SOHO at 08:30 UT on that day. In the EIT observation, one-half of the filament shows two stages of evolution: stage 1 is a slow, roughly constant upward movement at approximately 1 km/s lasting approximately 0.5 hr, and stage 2 is a rapid upward eruption at approximately 16 km/s occurring just before the filament disappears into interplanetary space. The other half of the filament shows little motion along the line of sight during the time of stage 1 but erupts along with the rest of the filament during stage 2. There is no obvious emission from the filament in the SXT observation until stage 2; at that time, an arcade of EUV and soft X-ray loops forms first at the central location of the filament and then expands outward along the length of the filament channel. A plot of EUV intensity versus time of the central portion of the filament (where the postflare loops initially form) shows a flat profile during stage 1 and a rapid upturn after the start of stage 2. This light curve is delayed from what would be expected if 'tether-cutting' reconnection in the core of the erupting region were responsible for the initiation of the eruption. Rather, these observations suggest that a loss of stability of the magnetic field holding the filament initiates the eruption, with reconnection in the core region occurring only as a by-product.

Sterling, Alphonse C.↗
NASA NTRS2006

Solar Wind Helium Abundance as a Function of Speed and Heliographic Latitude: Variation through a Solar Cycle

We present a study of the variation of the relative abundance of helium to hydrogen in the solar wind as a function of solar wind speed and heliographic latitude over the previous solar cycle. The average values of A(sub He), the ratio of helium to hydrogen number densities, are calculated in 25 speed intervals over 27-day Carrington rotations using Faraday Cup observations from the Wind spacecraft between 1995 and 2005. The higher speed and time resolution of this study compared to an earlier work with the Wind observations has led to the discovery of three new aspects of A(sub He), modulation during solar minimum from mid-1995 to mid-1997. First, we find that for solar wind speeds between 350 and 415 km/s, A(sub He), varies with a clear six-month periodicity, with a minimum value at the heliographic equatorial plane and a typical gradient of 0.01 per degree in latitude. For the slow wind this is a 30% effect. We suggest that the latitudinal gradient may be due to an additional dependence of coronal proton flux on coronal field strength or the stability of coronal loops. Second, once the gradient is subtracted, we find that A(sub He), is a remarkably linear function of solar wind speed. Finally, we identify a vanishing speed, at which A(sub He), is zero, is 259 km/s and note that this speed corresponds to the minimum solar wind speed observed at one AU. The vanishing speed may be related to previous theoretical work in which enhancements of coronal helium lead to stagnation of the escaping proton flux. During solar maximum the A(sub He), dependences on speed and latitude disappear, and we interpret this as evidence of two source regions for slow solar wind in the ecliptic plane, one being the solar minimum streamer belt and the other likely being active regions.

Kasper, J. C.↗