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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

Validation of the Pulmonary Function System for Use on the International Space Station

Aerobic deconditioning occurs during long duration space flight despite the use of exercise countermeasures (Convertino, 1996). As a part of International Space Station (ISS) medical operations, periodic tests designed to estimate aerobic capacity are performed to track changes in aerobic fitness and to determine the effectiveness of exercise countermeasures. These tests are performed prior to, during, and after missions of greater than 30 days in duration. Crewmembers selected for missions aboard the ISS perform a graded exercise test on a cycle ergometer approximately 270 days prior to their scheduled launch date in order to measure peak oxygen consumption (VO2PK) and peak heart rate (HRpk). Approximately 30 to 45 days prior to launch, crewmembers perform a submaximal cycle ergometer test at work rates set to elicit 25, 50 and 75% of their pre-flight VO2PK. This test, known as the Periodic Fitness Evaluation (PFE), serves as a baseline measure to which subsequent in-and post-flight exercise tests are compared. While onboard the ISS, crewmembers are normally scheduled to perform the PFE beginning with flight day (FD) 14 and every 30 days thereafter. The PFE is also conducted 5 and 30 days following flight. Using PFE data, aerobic fitness is estimated by quantifying the VO2 vs. HR relationship using linear regression and calculating the VO2 that would occur at the crewmember s previously measured HRpk. Currently, for data collected during flight, this technique assumes that the pre- vs. in-flight oxygen consumption per given cycle workload is similar. However, the validity of this assumption is based upon a sparse amount of data collected during the Skylab era (Michel, et al. 1977). The method of using heart rate and cycle ergometer work rates has been used to estimate aerobic fitness in normal gravity (Astrand and Ryhming, 1954; Lee, 1993). Due to spaceflight induced physiological alterations, such as shifts in extracellular fluid (e.g. plasma) volume, this method may not be valid during space flight. In addition, the ergometer onboard ISS is vibration-isolated and moves with the astronaut s application of force into the pedals. The effect of this movement on the VO2 of cycle exercise on ISS has not been quantified.

McCleary, Frank A.↗
NASA NTRS1990

Jovian H2 dayglow emission (1978-1989)

The IUE data set accumulated through 10 years of Jovian equatorial observations is used to measure the long-term temporal variation of the H2 dayglow emission. The model that best fits the data indicates a possible correlation between long-term solar activity and the Jovian H2 emission in the region 1500-1700 A between 1978 and 1989, which spans the decline in solar activity for solar cycle 21 and the rise in solar activity accompanying solar cycle 22. The magnitude of the observed variation is closer to that of the solar Ly-alpha flux than the 10.7 cm radio flux. Short-wavelength H2 band emission intensity is inconsistent with the amount of long-wavelength emission but may be reconciled if relatively low-energy excitation or fluorescence of solar radiation is invoked. No persistent longitudinal feature analogous to the H I Ly-alpha can be identified.

Mcgrath, M. A.↗
NASA NTRS1981

A two-temperature plasma distribution in the magnetosheath at lunar distances

Least squares Maxwellian fits have been made to data from the Apollo 15 suprathermal ion detector experiment (SIDE) during the moon's passage through the dusk magnetosheath. It is found that the data are best fit by superimposing two co-moving proton populations whose temperatures differ radically: kT roughly 10 eV and kT roughly 100 eV. This two-temperature distribution cannot be explained by alpha particles. The higher temperature population is typical of that expected for the fully shocked magnetosheath at lunar distances. The colder distribution could arise from cold plasma from within the magnetosphere brought up to magnetosheath flow speeds, but it is more probably due to unshocked solar wind.

Sanders, G. D.↗
NASA NTRS1984

The Shuttle Orbiter high resolution accelerometer package experiment - Preliminary flight results

A description of the High Resolution Accelerometer Package (HiRAP) experiment, designed to measure rarefied flow aerodynamic accelerations, is given. The ground test calibration factors, as well as post-flight data processing techniques to extract aerodynamic accelerations, are discussed and applied to the recorded reentry data of the recent STS-6 Shuttle Orbiter flight. The ratio of the measured normal-to-axial aerodynamic accelerations during reentry is used to obtain the first flight measurement of the lift-to-drag ratio (L/D) of a winged entry vehicle in the rarefied flow flight regime. The preliminary result for the free-molecule flow L/D is 0.10 + or - 0.03. The initial flight results on L/D are compared with current predictions which are based upon theoretical and empirical considerations. The measured free-molecule flow L/D value is higher than predicted by a factor of about three, indicating that surface reflection is not completely diffuse as currently assumed. In the rarefied flow transition regime, the Shuttle data book-bridging formula fits the flight data adequately. Upper altitude density profiles are also deduced from the measurements and presented. The density profiles show a wave phenomena with amplitude of about 60 percent, relative to a standard model.

Blanchard, R. C.↗
NASA NTRS1989

A voice-actuated wind tunnel model leak checking system

A computer program has been developed that improves the efficiency of wind tunnel model leak checking. The program uses a voice recognition unit to relay a technician's commands to the computer. The computer, after receiving a command, can respond to the technician via a voice response unit. Information about the model pressure orifice being checked is displayed on a gas-plasma terminal. On command, the program records up to 30 seconds of pressure data. After the recording is complete, the raw data and a straight line fit of the data are plotted on the terminal. This allows the technician to make a decision on the integrity of the orifice being checked. All results of the leak check program are stored in a database file that can be listed on the line printer for record keeping purposes or displayed on the terminal to help the technician find unchecked orifices. This program allows one technician to check a model for leaks instead of the two or three previously required.

Larson, William E.↗
NASA NTRS1994

Mirages and the nature of Pluto's atmosphere

We present model occultation lightcurves demonstrating that a strong thermal inversion layer at the base of Pluto's stratosphere can reproduce the minimum flux measured by the Kuiper Airborne Observatory (KAO) during the 1988 occultation of a star by Pluto. The inversion layer also forms the occultation equivalent of a mirage at a radius of 1198 km, which is capable of hiding tropospheres of significant depth. Pluto's surface lies below 1198 km, its radius depending on the depth of the troposphere. We begin by computing plausible temperature structures for Pluto's lower atmosphere, constrained by a calculation of the temperature of the atmosphere near the surface. We then trace rays from the occulted star through the model atmosphere, computing the resultant bending of the ray. Model light curves are obtained by summing the contribution of individual rays within the shadow of Pluto on Earth. We find that we can reproduce the KAO lightcurve using model atmospheres with a temperature inversion and no haze. We have explored models with tropospheres as deep as 40 km (implying a Pluto radius of 1158 km) that reproduce the suite of occultation data. Deeper tropospheres can be fitted to the data, but the mutual event radius of 1150 km probably provides a lower bound. If Pluto has a shallow or nonexistent troposphere, its density is consistent with formation in the solar nebula with modest water loss due to impact ejection. If the troposhere is relatively deep, implying a smaller radius and larger density, significant amounts of water loss are required.

Stansberry, J. A.↗
NASA NTRS1997

Response properties of pigeon otolith afferents to linear acceleration

In the present study, the sensitivity to sinusoidal linear accelerations in the plane of the utricular macula was tested in afferents. The head orientation relative to the translation axis was varied in order to determine the head position that elicited the maximal and minimal responses for each afferent. The response gain and phase values obtained to 0.5-Hz and 2-Hz linear acceleration stimuli were then plotted as a function of head orientation and a modified cosine function was fit to the data. From the best-fit cosine function, the predicted head orientations that would produce the maximal and minimal response gains were estimated. The estimated maximum response gains to linear acceleration in the utricular plane for the afferents varied between 75 and 1420 spikes s-1 g-1. The mean maximal gains for all afferents to 0.5-Hz and 2-Hz sinusoidal linear acceleration stimuli were 282 and 367 spikes s-1 g-1, respectively. The minimal response gains were essentially zero for most units. The response phases always led linear acceleration and remained constant for each afferent, regardless of head orientation. These response characteristics indicate that otolith afferents are cosine tuned and behave as one-dimensional linear accelerometers. The directions of maximal sensitivity to linear acceleration for the afferents varied throughout the plane of the utricle; however, most vectors were directed out of the opposite ear near the interaural axis. The response dynamics of the afferents were tested using stimulus frequencies ranging between 0.25 Hz and 10 Hz (0.1 g peak acceleration). Across stimulus frequencies, most afferents had increasing gains and constant phase values. These dynamic properties for individual afferents were fit with a simple transfer function that included three parameters: a mechanical time constant, a gain constant, and a fractional order distributed adaptation operator.

Non-NASA Center↗
NASA NTRS1976

Absolute rate parameters for the reaction of atomic hydrogen with hydrazine

Absolute rate parameters for the reaction of atomic hydrogen with hydrazine H + N2H4 yields H2 + N2H3 have been determined in a direct manner using flash photolysis of dilute mixtures of hydrazine in helium and time dependent observation of H via resonance fluorescence. By measuring the H-atom decay under pseudo-first-order conditions, the bimolecular rate constant K sub 1 was obtained over the temperature range 228-400 K. The data were fitted with good linearity to the Arrhenius expression K sub 1 = (9.87 plus or minus 1.17) x 10 to the -12th exp(-2380 plus or minus 100/RT) cu cm/molecule/s. The data were shown to be free of any contributions from secondary reactions involving H as a reactant or product.

Stief, L. J.↗
NASA NTRS1998

Application of Parametrized Post-Newtonian Methods to the Gravitational IS of Satellite Energy Exchange Data

Project Satellite Energy Exchange (SEE) is a free-flying, high altitude satellite that utilizes space to construct a passive, low-temperature, nano-g environment in order to accurately measure the poorly known gravitational constant G plus other gravitational parameters that are difficult to measure in an earth-based laboratory. Eventually data received from SEE must be analyzed using a model of the gravitational interaction including parameters that describe deviations from general relativity and experiment. One model that can be used to fit tile data is the Parametrized post- Newtonian (PPN) approximation of general relativity (GR) which introduces ten parameters which have specified values in (GR). It is the lowest-order, consistent approximation that contains non linear terms. General relativity predicts that the Robertson parameters, gamma (light deflection), and beta (advance of the perihelion), are both 1 in GR. Another eight parameters, alpha(sub k), k=1,2,3 and zeta(sub k), k=1,2,3,4 and Xi are all zero in GR. Non zero values for alpha(sub k) parameters predict preferred frame effects; for zeta(sub k) violations of globally conserved quantities such as mass, momentum and angular momentum; and for Xi a contribution from the Whitehead theory of gravitation, once thought to be equivalent to GR. In addition, there is the possibility that there may be a preferred frame for the universe. If such a frame exists, then all observers must measure the velocity omega of their motion with respect to this universal rest frame. Such a frame is somewhat reminiscent of the concept of the ether which was supposedly the frame in which the velocity of light took the value c predicted by special relativity. The SEE mission can also look for deviations from the r(exp -2) law of Newtonian gravity, adding parameters alpha and lamda for non Newtonian behavior that describe the magnitude and range of the r(exp -2) deviations respectively. The foundations of the GR supposedly agree with Newtonian gravity to first order so that the parameters alpha and lamda are zero in GR. More important, however, GR subsequently depends on this Newtonian approximation to build up the non linear higher-order terms which forms the basis of the PPN frame work.

Smalley, Larry L.↗
NASA NTRS2000

Role of muscle pulleys in producing eye position-dependence in the angular vestibuloocular reflex: a model-based study

It is well established that the head and eye velocity axes do not always align during compensatory vestibular slow phases. It has been shown that the eye velocity axis systematically tilts away from the head velocity axis in a manner that is dependent on eye-in-head position. The mechanisms responsible for producing these axis tilts are unclear. In this model-based study, we aimed to determine whether muscle pulleys could be involved in bringing about these phenomena. The model presented incorporates semicircular canals, central vestibular pathways, and an ocular motor plant with pulleys. The pulleys were modeled so that they brought about a rotation of the torque axes of the extraocular muscles that was a fraction of the angle of eye deviation from primary position. The degree to which the pulleys rotated the torque axes was altered by means of a pulley coefficient. Model input was head velocity and initial eye position data from passive and active yaw head impulses with fixation at 0 degrees, 20 degrees up and 20 degrees down, obtained from a previous experiment. The optimal pulley coefficient required to fit the data was determined by calculating the mean square error between data and model predictions of torsional eye velocity. For active head impulses, the optimal pulley coefficient varied considerably between subjects. The median optimal pulley coefficient was found to be 0.5, the pulley coefficient required for producing saccades that perfectly obey Listing's law when using a two-dimensional saccadic pulse signal. The model predicted the direction of the axis tilts observed in response to passive head impulses from 50 ms after onset. During passive head impulses, the median optimal pulley coefficient was found to be 0.21, when roll gain was fixed at 0.7. The model did not accurately predict the alignment of the eye and head velocity axes that was observed early in the response to passive head impulses. We found that this alignment could be well predicted if the roll gain of the angular vestibuloocular reflex was modified during the initial period of the response, while pulley coefficient was maintained at 0.5. Hence a roll gain modification allows stabilization of the retinal image without requiring a change in the pulley effect. Our results therefore indicate that the eye position-dependent velocity axis tilts could arise due to the effects of the pulleys and that a roll gain modification in the central vestibular structures may be responsible for countering the pulley effect.

NASA Discipline Neuroscience↗
NASA NTRS2019

The First Swift Intensive AGN Accretion Disk Reverberation Mapping Survey

Swift intensive accretion disk reverberation mapping of four AGN yielded light curves sampled ∼200–350 times in 0.3–10 keV X-ray and six UV/optical bands. Uniform reduction and cross-correlation analysis of these data sets yields three main results: (1) The X-ray/UV correlations are much weaker than those within the UV/optical, posing severe problems for the lamp-post reprocessing model in which variations in a central X-ray corona drive and power those in the surrounding accretion disk. (2) The UV/optical interband lags are generally consistent with t μ l4 3 as predicted by the centrally illuminated thin accretion disk model. While the average interband lags are somewhat larger than predicted, these results alone are not inconsistent with the thin disk model given the large systematic uncertainties involved. (3) The one exception is the U band lags, which are on average a factor of ∼2.2 larger than predicted from the surrounding band data and fits. This excess appears to be due to diffuse continuum emission from the broad-line region (BLR). The precise mixing of disk and BLR components cannot be determined from these data alone. The lags in different AGN appear to scale with mass or luminosity. We also find that there are systematic differences between the uncertainties derived by JAVELIN versus more standard lag measurement techniques, with JAVELIN reporting smaller uncertainties by a factor of 2.5 on average. In order to be conservative only standard techniques were used in the analyses reported herein.

R. Edelson↗
NASA NTRS1979

The interstellar oxygen edge in the X-ray spectrum of the Crab Nebula

Measurement of the X-ray spectrum of the Crab Nebula by the HEAO 1 A-2 low-energy (0.15-3 keV) detectors is reported. The spectral restoration techniques described by Blissett and Cruise (1979) and Kahn and Blissett (1979) are used to demonstrate explicitly the existence of a 'negative' feature near 0.5 keV that is consistent with the edge expected due to absorption by interstellar oxygen. For a simple power-law model with photon index -2.08, the data require a column density of 3.0 + or - 0.1 x 10 to the 21st per sq cm and an oxygen abundance of 1.0 + or - 0.1 times the Brown and Gould (1970) value. Satisfactory fits can also be achieved with the more sophisticated Fireman (1974) models, but no model can be adjusted to fit the data without the inclusion of interstellar oxygen.

Charles, P. A.↗
NASA NTRS1993

The warped disk of Centaurus A in the near-infrared

We present infrared images of Cen A (NGC 5128) in the J, H, and K bands. The infrared morphology is primarily determined by the presence of a thin absorptive warped disk. By integrating the light of the underlying prolate galaxy through such a disk, we construct models which we compare with infrared and X-ray data. The geometry of the warped disk needed to fit the IR data is consistent with a warped disk which has evolved as a result of differential precession in a prolate potential. The disk has an inclination, with respect to the principal axis of the underlying elliptical galaxy, that is higher at larger radii than in the inner region. A scenario is proposed where a small gas-rich galaxy infalling under the force of dynamical friction is tidally stripped. Stripping occurs at different times during its infall. The orientation of the resulting gas disk depends upon the angular momentum of the infalling galaxy. We find that the resulting precession angle of the disk is well described by the precession model, but that the inclination angle may vary as a function of radius. We propose an orbit for the infalling galaxy that is consistent with the geometry of the warped disk needed to fit our infrared data, and rotation observed in the outer part of the galaxy.

Quillen, A. C.↗
NASA NTRS1972

Analysis of flight test transition and turbulent heating data. Part 2: Turbulent heating results

The results of three turbulent heating predictions (Van Driest II, Spalding-Chi, and Walker Eckert reference enthalpy) have been compared to the data of several re-entry vehicles. Details and comparisons of each technique with the data are presented. The data analyzed cover a range of local Mach numbers of 3.3 to 15.2, wall to boundary layer edge temperature ratio of 0.46 to 2.6 and local Reynolds number of 7 times 10 to the 6th power to 5.3 times 10 to the 8th power. Data were transformed to an incompressible plane, using the prediction methods above, and compared with the Colburn and von Karman forms of the Reynolds analogy. The results indicate that the reference enthalpy technique best fits the data when the Colburn analogy was used; whereas, the Van Driest II method agrees with both forms of the Reynolds analogy. The Spalding-Chi method tends to under predict the data. Finally, there does not appear to be any significant difference when comparing the incompressible Stanton number as a function of Renolds number based on either wetted length or momentum thickness.

Laganelli, A. L.↗
NASA NTRS1975

Polynomial coefficients of thermochemical data for the C-H-O-N system

Thermodynamic data are required input for the finite kinetics and equilibrium computer programs needed for modeling the combustion of hydrocarbons in the fields of energy and pollution research. Least squares determined coefficients of the curve-fitted thermodynamic data for 193 species in the C-H-O-N system are presented in card image form and are of suitable format for use by common computer programs.

Wakelyn, N. T.↗
NASA NTRS1981

Mars - Hellas Planitia gravity analysis

Doppler radio tracking data from Viking Orbiter 1 has provided new detailed observations of gravity variations over Hellas Planitia. Line-of-sight Bouguer gravity definitely indicates that isostatic adjustment has occurred. Two theoretical models were tested to obtain fits to the gravity data. Results for a surface deficit model, and a model with a surface deficit and a mass excess at depth are displayed. The mass-at-depth model produced very marked improvement in the data fit as compared to the surface deficit model. The optimum depth for the mass excess is 130 km.

Sjogren, W. L.↗
NASA NTRS1990

Threshold altitude resulting in decompression sickness

A review of case reports, hypobaric chamber training data, and experimental evidence indicated that the threshold for incidence of altitude decompression sickness (DCS) was influenced by various factors such as prior denitrogenation, exercise or rest, and period of exposure, in addition to individual susceptibility. Fitting these data with appropriate statistical models makes it possible to examine the influence of various factors on the threshold for DCS. This approach was illustrated by logistic regression analysis on the incidence of DCS below 9144 m. Estimations using these regressions showed that, under a noprebreathe, 6-h exposure, simulated EVA profile, the threshold for symptoms occurred at approximately 3353 m; while under a noprebreathe, 2-h exposure profile with knee-bends exercise, the threshold occurred at 7925 m.

Kumar, K. V.↗
NASA NTRS1987

Experimental data correlations for the effects of rotation on impingement cooling of turbine blades

The effects of rotation on impingement cooling have been experimentally studied under simulated gas turbine operating conditions. A large scale model of a blade is spun in vacuum. External heating is simulated by resistve dissipation in the thin wall of the model, which is impingement cooled. The local internal Nu is measured by an IR radiometric technique with high spatial resolution. At low rotational speeds the data agree well with published measurements taken under stationary conditions. At higher speeds, a decrease in the average Nu by up to 20-30 percent is observed. Severe gradients are generated near the hub region. Empirical correlations, which fit the data well and render it more useful for design purposes, are presented. Measurements and correlations suggest that rotational effects are very important and can cause premature blade failure.

Kreatsoulas, J. C.↗