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At least 613 records · Page 34

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NASA NTRS1983

The GEMPAK Barnes interactive objective map analysis scheme

The analysis scheme and meteorological applications of the GEMPAK data analysis and display software system developed by NASA are described. The program was devised to permit objective, versatile, and practical analysis of satellite meteorological data using a minicomputer and a display system with graphics capability. A data area can be selected within the data file for the globe, and data-sparse regions can be avoided. Distances between observations and the nearest observation points are calculated in order to avoid errors when determining synoptic weather conditions. The Barnes (1973) successive correction method is employed to restore the amplitude of small yet resolvable wavelengths suppressed in an initial filtering pass. The rms deviation is then calculated in relation to available measured data. Examples are provided of treatment of VISSR data from the GOES satellite and a study of the impact of incorrect cloud height data on synoptic weather field analysis.

Koch, S. E.↗

NASA NTRS1983

Tibial changes in experimental disuse osteoporosis in the monkey

The mechanical properties and structural changes in the monkey tibia with disuse osteoporosis and during subsequent recovery are investigated. Bone mending stiffness is evaluated in relation to microscopic changes in cortical bone and Norland bone mineral analysis. Restraint in the semireclined position is found to produce regional losses of bone most obviously in the anterior-proximal tibiae. After six months of restraint, the greatest losses of bone mineral in the proximal tibiae range from 23 percent to 31 percent; the largest changes in bone stiffness range from 36 percent to 40 percent. Approximately eight and one-half months of recovery are required to restore the normal bending properties. Even after 15 months of recovery, however, the bone mineral content does not necessarily return to normal levels. Histologically, resorption cavities in cortical bone are seen within one month of restraint; by two and one-half months of restraint there are large resorption cavities subperiosteally, endosteally, and intracortically. After 15 months of recovery, the cortex consists mainly of first-generation haversian systems. After 40 months, the cortex appears normal, with numerous secondary and tertiary generations of haversian systems.

Young, D. R.↗

NASA NTRS1983

A simple example of a classical gauge transformation

Attention is given to the manner in which the interaction of a gravitational field with a diffusing gas is induced by a gauge transformation. Since the gas can be thought of as a field, the diffusion process may be represented by a Lagrangian density with the symmetry property of invariance under translation. While this property is lost when the field interacts with a static gravitational field, it is formally restored when an appropriate gauge transformation is performed. This ascription of field properties to a gas offers an illuminating illustration of the coupling of matter to a gauge field within the context of classical mechanics.

Whitten, R. C.↗

NASA NTRS1983

The Voyager 2 scan platform anomaly

The two Voyager spacecraft were launched in the summer of 1977, flew past Jupiter in 1979, and reached Saturn in 1980 and 1981. The Voyager Attitude and Articulation Control Subsystem (AACS) controls the positioning of a scan platform on which scientific instruments are mounted. On August 26, 1981, it was discovered that the azimuth axis of the scan platform of Voyager 2 had not completed the commanded slew. The profile of the failed slew command resembled a similar scan failure on Voyager 1 on February 23, 1979. In that case, contamination of the output gear mesh in the azimuth actuator was identified as the most probable cause of the failure. The problem was solved by cycling the azimuth actuator until the contaminant broke down and smooth operation was restored. A similar treatment applied to the Voyager 2 problem failed. Details of the Voyager 2 anomaly investigation are discussed.

Marchetto, C. A.↗

NASA NTRS1985

Reversing Optical Damage In LiNbO3 Switches

One symptom of optical damage in Ti-diffused LiNbO3 directional-coupler switch reversed by temporarily raising input illumination to higher-thannormal power level. Healing phenomenon used to restore normal operation, increase operating-power rating, and stabilize operating characteristics at lower powers. Higher operating power is tolerated after treatment.

Gee, C. M.↗

NASA NTRS1983

Control of the forebody vortex orientation by asymmetric air injection. Part A: Application to enhance departure/spin recovery of fighter aircraft and Part B: Details of the flow structure

A concept developed to provide powerful directional control effectiveness for a fighter aircraft at high angles of attack is described. The concept utilizes the energy concentrated in the strong forebody vortices (which form on slender bodies of high relative incidence) by controlling the lateral orientation of the vortices with respect to the body. The objective was to utilize the side force associated with asymmetric vortices, in a controlled manner, to enhance the ability of the fighter to recover from a departure from controlled flight. The results from water tunnel and wind tunnel experiments show that a small amount of tangential blowing along the forebody near the apex can effectively alter the forebody vortex system and generate large restoring yawing moments. Six degree of freedom digital simulation results show that this concept can substantially enhance recovery characteristics of fighter aircraft with long, slender forebodies. Also, the results of experiments which were conducted on a cone model are discussed where the principal test objective was to develop an understanding of the fluid mechanics involved in the process of vortex control. Knowledge gained in these more generic tests should allow the concept to be applied to a wider range of configurations.

Skow, A. M.↗

NASA NTRS1983

Modeling of transient disturbances in coronal-streamer configurations

Numerical simulations of the formation and propagation of mass ejection, loop transients in coronal streamers are discussed. The simulations are accomplished with numerical solutions of the single fluid, ideal MHD equations of motion in the meridional plane. The streamer is produced by simulating the relaxation of an initially radial hydrodynamic flow coupled with a dipole magnetic field. The simulated transient then results from an energy release at the base of the streamer. The legs of the loop transient produced remain essentially stationary while the loop expands mainly in the radial direction with velocities of 400 to 750 km s-1. Once the leading edge of the transient has passed out of the lower corona, the initial streamer configuration is restored after 15 to 24 hours. A second energy release 2 hours later than, and with an energy release identical to, the first does not produce a significant coronal disturbance.

Steinolfson, R. S.↗

NASA NTRS1983

Atomization and combustion performance of antimisting kerosene and jet fuel

Combustion performance of antimisting kerosene (AMK) containing FM-9 polymer was investigated at various levels of degradation (restoration of AMK for normal use in a gas turbine engine). To establish the relationship of degradation and atomization to performance in an aircraft gas turbine combustor, sprays formed by the nozzle of a JT8-D combustor with Jet A and AMK at 1 atmosphere (atm) (14.1 lb/square in absolute) pressure and 22 C at several degradation levels were analyzed. A new spray characterization technique based on digital image analysis of high resolution, wide field spray images formed under pulsed ruby laser sheet illumination was developed. Combustion tests were performed for these fuels in a JT8-D single can combustor facility to measure combustion efficiency and the lean extinction limit. Correlation of combustion performance under simulated engine operating conditions with nozzle spray Sauter mean diameter (SMD) measured at 1 atm and 22 C were observed. Fuel spray SMD and hence the combustion efficiency are strongly influenced by fuel degradation level. Use of even the most highly degraded AMK tested (filter ratio = 1.2) resulted in an increase in fuel consumption of 0.08% to 0.20% at engine cruise conditions.

Fleeter, R.↗

NASA NTRS1984

Ohmic Versus Rectifying Contacts of Au to N-gaas by Ion Sputtering

Results of investigations of argon ion sputtering of heavily doped n-GaAs are compared with those obtained from studies of Au/low doping density n-GaAs contacts. The Au contact on Si-doped GaAs was nearly ohmic when the surface contamination (carbon and oxides) was reduced prior to deposition by chemical cleaning. However, when ion sputtering was used in situ to clean the surface, rectifying contact was produced whose barrier height varied with the energy of the sputtering ion. It was found that ion sputtering of GaAs doped to more than 3 x 10 to the 18th power/cu may be used to change ohmic contact to rectifying contacts. The barrier height may be changed by changing the ion energy. The behavior results from the sputter creation of deep level acceptor states at the GaAs surface. Annealing after sputtering can restore the contact to nearly an ohmic character.

Wang, Y. X.↗

NASA NTRS1984

The role of cobalt on the creep of Waspaloy

Cobalt was systematically replaced with nickel in Waspaloy (which normally contains 13% Co) to determine the effects of cobalt on the creep behavior of this alloy. Effects of cobalt were found to be minimal on tensile strengths and microstructure. The creep resistance and the stress rupture resistance determined in the range from 704 to 760 C (1300 to 1400 C) were found to decrease as cobalt was removed from the standard alloy at all stresses and temperatures. Roughly a ten-fold drop in rupture life and a corresponding increase in minimum creep rate were found under all test conditions. Both the apparent creep activation energy and the matrix contribution to creep resistance were found to increase with cobalt. These creep effects are attributed to cobalt lowering the stacking fault energy of the alloy matrix. The creep resistance loss due to the removal of cobalt is shown to be restored by slightly increasing the gamma' volume fraction. Results are compared to a previous study on Udimet 700, a higher strength, higher gamma' volume fraction alloy with similar phase chemistry, in which cobalt did not affect creep resistance. An explanation for this difference in behavior based on interparticle spacing and cross-slip is presented.

Jarrett, R. N.↗

NASA NTRS1984

Simulation and assimilation of satellite altimeter data at the oceanic mesoscale

An improved "objective analysis' technique is used along with an altimeter signal statistical model, an altimeter noise statistical model, an orbital model, and synoptic surface current maps in the POLYMODE-SDE area, to evaluate the performance of various observational strategies in catching the mesoscale variability at mid-latitudes. In particular, simulated repetitive nominal orbits of ERS-1, TOPEX, and SPOT/POSEIDON are examined. Results show the critical importance of existence of a subcycle, scanning in either direction. Moreover, long repeat cycles ( 20 days) and short cross-track distances ( 300 km) seem preferable, since they match mesoscale statistics. Another goal of the study is to prepare and discuss sea-surface height (SSH) assimilation in quasigeostrophic models. Restored SSH maps are shown to meet that purpose, if an efficient extrapolation method or deep in-situ data (floats) are used on the vertical to start and update the model.

Demay, P.↗

NASA NTRS1984

Stability and Convergence of Underintegrated Finite Element Approximations

The effects of underintegration on the numerical stability and convergence characteristics of certain classes of finite element approximations were analyzed. Particular attention is given to hourglassing instabilities that arise from underintegrating the stiffness matrix entries and checkerboard instabilities that arise from underintegrating constrain terms such as those arising from incompressibility conditions. A fundamental result reported here is the proof that the fully integrated stiffness is restored in some cases through a post-processing operation.

Oden, J. T.↗

NASA NTRS1984

A Study of DSN Traveling Wave Maser System Reliability

Reliability and availability characteristics of the DSN traveling wave maser (TWM) Assemblies are reported for the years 1981 through 1983, the charcteristics determined are: mean time between failures (MTBF) - 1200 hours; mean time to restore service (MTTRS) - 2.5 hours; and availability - 99.83%. The TWM MTBF is very good as compared to other DSN subsystems and assemblies. The TWM MTTRS is currently about three times as long as the average of other DSN subsystems. The dominant cause of TWM failures is contamination of the helium gas in the closed cycle refrigerators. Station configurations that do not provide TWM redundancy are subject to reception outages for long periods of time. Recommendations are made to improve the TWM Assembly availability characteristics for future mission support operations.

Stevens, R.↗

NASA NTRS1984

Pipelined digital SAR azimuth correlator using hybrid FFT-transversal filter

A synthetic aperture radar system (SAR) having a range correlator is provided with a hybrid azimuth correlator which utilizes a block-pipe-lined fast Fourier transform (FFT). The correlator has a predetermined FFT transform size with delay elements for delaying SAR range correlated data so as to embed in the Fourier transform operation a corner-turning function as the range correlated SAR data is converted from the time domain to a frequency domain. The azimuth correlator is comprised of a transversal filter to receive the SAR data in the frequency domain, a generator for range migration compensation and azimuth reference functions, and an azimuth reference multiplier for correlation of the SAR data. Following the transversal filter is a block-pipelined inverse FFT used to restore azimuth correlated data in the frequency domain to the time domain for imaging.

Wu, C.↗

NASA NTRS1984

MHD stability of compressible coronal loops with radiative energy loss

The effect of radiative energy loss on the stability of compressible plasma in coronal loops is studied. By taking the limit as poloidal wavenumber m approaches infinity, stability conditions for local modes are derived. It was found that the radiation effect can trigger MHD instabilities of coronal loops which are in ideally marginally stable states. Compressibility is a stabilizing effect for ideal MHD local modes because the compression of magnetic field lines exerts a restoring force by increasing magnetic pressure. Compression of plasma induces two modes in a radiatively unstable plasma, magnetosonic and condensation modes. Compressibility affects the stability of ideally stable (or unstable) coronal plasmas through magnetosonic modes, which are a stabilizing (destabilizing) effect for ideally stable (unstable) plasmas. For coronal plasmas in ideally marginally stable states, condensation as well as magnetosonic modes can trigger MHD instability. Because of these two modes, the effect of radiation on compressible coronal plasmas is more destabilizing than it is on incompressible plasmas when the plasmas are in ideal MHD unstable or marginally stable states.

An, C.-H.↗

NASA NTRS1983

The effects of immobilization on cortical bone in monkeys (M. nemestrina)

Rhesus and pigtail monkeys were restrained for up to seven months in a hypogravic-hypodynamic environment for the purpose of studying the osteoporotic process and its reversibility, particularly in relation to humans. In vivo bending, radiography and tomography are among the techniques that were used. Bone deterioration within one month was detectable only in histological preparation, where resorption and subsequent cavity formation were demonstrated in addition to demineralization of the remaining hard tissue. Norland bone mineral analysis showed the greatest bone demineralization in the proximal tibia (23 percent to 31 percent after six months restraint), recovery did not even necessarily occur after 15 months. The largest bone stiffness decrease was 36 to 40 percent after a six months restraint; normal bending properties but not mineral content were restored after 8-1/2 months. Contrary to earlier studies, it is concluded that bone recovery, though a lengthy process, is possible: cortical bone in the tibia required 40 months.

Niklowitz, W. J.↗

NASA NTRS1984

Heating experiments for flowability improvement of near-freezing aviation fuel

An experimental jet fuel with a -33 C freezing point was chilled in a wing tank simulator with superimposed fuel heating to improve low temperature flowability. Heating consisted of circulating a portion of the fuel to an external heat exchanger and returning the heated fuel to the tank. Flowability was determined by the mass percent of unpumpable fuel (holdup) left in the simulator upon withdrawal of fuel at the conclusion of testing. The study demonstrated that fuel heating is feasible and improves flowability as compared to that of baseline, unheated tests. Delayed heating with initiation when the fuel reaches a prescribed low temperature limit, showed promise of being more efficient than continuous heating. Regardless of the mode or rate of heating, complete flowability (zero holdup) could not be restored by fuel heating. The severe, extreme-day environment imposed by the test caused a very small amount of subfreezing fuel to be retained near the tank surfaces even at high rates of heating. Correlations of flowability established for unheated fuel tests also could be applied to the heated test results if based on boundary-layer temperature or a solid index (subfreezing point) characteristic of the fuel. Previously announced in STAR as N82-26483

Friedman, R.↗

NASA NTRS1986

Dent-Removing Tool

Small dents in metal parts and structures evened out quickly with aid of simple tool. User first tack welds tip of slide rod to dent. Next, user slides hammer away from dent so hammer strikes flange at end of rod. Impact of hammer pulls out dent. Hammering repeated until dented metal even with surrounding surface. Slide rod unwelded, and surface finish restored.

Leipham, T.↗