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At least 307 records · Page 17

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NASA NTRS1991

Effects of shifts in the level of automation on operator performance

The results of two experiments examining the effects of shifts in the type and level of automation on operator performance are presented. The first examines the costs and benefits of adaptive-automation shifts on operator performance, while the second experiment examines the effects of variations in automation reliability on operator detection of automation failures. Performance consequences of complacency in system monitoring are shown to be related to characteristics of the monitoring task automation, i.e., automation reliability and consistency.

Parasuraman, Raja↗

NASA NTRS1991

Progress in speckle-shift strain measurement

The Instrumentation and Control Technology Division of the Lewis Research Center has been developing an in-house capability to make one dimensional and two dimensional optical strain measurements on high temperature test specimens. The measurements are based on a two-beam speckle-shift technique. The development of composite materials for use in high temperature applications is generating interest in using the speckle-shift technique to measure strains on small diameter fibers and wires of various compositions. The results of preliminary speckle correlation tests on wire and fiber specimens are covered, and the advanced system currently under development is described.

Lant, Christian T.↗

NASA NTRS1993

Air-mass flux measurement system using Doppler-shifted filtered Rayleigh scattering

An optical system has been investigated to measure mass flux distributions in the inlet of a high speed air-breathing propulsion system. Rayleigh scattered light from air is proportional to the number density of molecules and hence can be used to ascertain the gas density in a calibrated system. Velocity field measurements are achieved by spectrally filtering the elastically-scattered Doppler-shifted light with an absorbing molecular filter. A novel anamorphic optical collection system is used which allows optical rays from different scattering angles, that have different Doppler shifts, to be recorded separately. This is shown to obviate the need to tune the laser through the absorption to determine velocities, while retaining the ability to make spatially-resolved measurements along a line. By properly selecting the laser tuning and filter parameters, simultaneous density measurements can be made. These properties are discussed in the paper and experiments demonstrating the velocimetry capability are described.

Shirley, John A.↗

NASA NTRS1993

Rotational level-dependent collisional broadening and line shift of the A2Sigma(+)-X2Pi (1,0) band of OH in hydrogen-air combustion gases

Measurements of the collisional broadening and line shift of the (1,0) band of the A2Sigma(+)-X2Pi system of OH are reported in atmospheric pressure hydrogen-air combustion gases. The measurements were made using a single-mode, narrow linewidth, frequency-doubled ring dye laser operating near 283 nm. The OH was generated in the combustion gases of a flat flame H2-air burner. Collisional broadening parameters for equilibrium mixtures of H2, O2, H2O, and N2 were obtained spanning a range of fuel/air equivalence ratios from 0.6 to 1.6 and temperatures from 1500 to 2050 K. Measurements were obtained spanning rotational quantum numbers from 4.5 to 16.5. The collision induced frequency shift was determined to be 0.1 that of the collisional broadening.

Kessler, W. J.↗

NASA NTRS1993

Hydrogen broadening and collision-induced line shifts of methane at 4200/cm

Many of the lines of the nu1 + nu4 and nu3 + nu4 bands of methane in the vicinity of 4200/cm have been assigned and are reported in the HITRAN data-base which is commonly used for atmospheric transmission calculations in the IR. The collision-induced broadening coefficients of hydrogen for more than 200 of these lines are reported. Also, by using the water-vapor lines which occur in the spectra as calibration marks, the frequencies of the broadened lines are determined. This permitted the collision-induced line shifts to be measured for lines sufficiently isolated from interfering blends: all of the shifts which could be reliably determined in this way were negative.

Margolis, Jack S.↗

NASA NTRS1993

Air-, N2-, and O2-broadening and shift coefficients in the nu(3) spectral region of (C-12)H4

Results are presented of an analysis of 29 room-temperature laboratory absorption spectra of a dilute CH4 sample in dry air, N2, and O2 at total pressures ranging from 60 to 550 torr, yielding values of pressure-broadening and pressure-induced-shift coefficients for more than 450 vibration-rotation transitions in the nu(3), nu(2) + nu(4), and 2nu(2)-super-2 bands of (C-12)H4. Comparisons of the present results for the nu(3) and nu(2) + nu(4) bands with previous measurements on other bands and isotopes of CH4 show that, for a given transition, broadening by air and N2 are nearly equal, and broadening by O2 is smaller by less than 10 percent. It is also found that the pressure shift coefficients are more vibrational dependent than the pressure broadening coefficients.

Benner, D. C.↗

NASA NTRS1993

A comparison between coherent and noncoherent mobile systems in large Doppler shift, delay spread, and C/I environment

The performance and implementation complexity of coherent and of noncoherent QPSK and GMSK modulation/demodulation techniques in a complex mobile satellite systems environment, including large Doppler shift, delay spread, and low C/I, are compared. We demonstrate that for large f(sub d)T(sub b) products, where f(sub d) is the Doppler shift and T(sub b) is the bit duration, noncoherent (discriminator detector or differential demodulation) systems have a lower BER floor than their coherent counterparts. For significant delay spreads, e.g., tau(sub rms) greater than 0.4 T(sub b), and low C/I, coherent systems outperform noncoherent systems. However, the synchronization time of coherent systems is longer than that of noncoherent systems. Spectral efficiency, overall capacity, and related hardware complexity issues of these systems are also analyzed. We demonstrate that coherent systems have a simpler overall architecture (IF filter implementation-cost versus carrier recovery) and are more robust in an RF frequency drift environment. Additionally, the prediction tools, computer simulations, and analysis of coherent systems is simpler. The threshold or capture effect in low C/I interference environment is critical for noncoherent discriminator based systems. We conclude with a comparison of hardware architectures of coherent and of noncoherent systems, including recent trends in commercial VLSI technology and direct baseband to RF transmit, RF to baseband (0-IF) receiver implementation strategies.

Feher, Kamilo↗

NASA NTRS1992

Venous compliance and fluid shift measurements on Spacelab IML-1

During the first few hours of a human spaceflight mission, a headward fluid shift out of the abdomen, pelvis, and legs initiates a number of adaptive cardiovascular responses, including a loss of intravascular and extravascular fluid volume. On return to earth, these cardiovascular changes may lead to debilitating symptoms of orthostatic intolerance in an unprotected astronaut. To test the hypothesis that an inflight increase in compliance of the leg veins may contribute to this condition, measurements of lower leg fluid shift and bulk venous compliance were collected from crew members during the eight-day First International Microgravity Laboratory shuttle mission. An ultrasonic limb plethysmograph, in conjunction with two compression cuffs encircling the calf and thigh, was used to determine bulk compliance of the underlying veins over a range of negative and positive transmural pressures. The data from inflight experiment sessions were compared to preflight and postflight sessions. The preliminary results indicate that the volume of the lower leg decreased by over 10 percent by the sixth day of flight, but there was no apparent change in venous compliance.

Leiski, D.↗

NASA NTRS1993

Using AVIRIS for in-flight calibration of the spectral shifts of SPOT-HRV and of AVHRR?

The response of a satellite sensor varies during its lifetime; internal calibration devices can be used to follow the sensor degradation or in-flight calibrations are conducted from estimates of the radiance at satellite level for well predictable situations. Changes in gain are evaluated assuming that the spectral response of the sensor is stable with time; i.e., that the filter response as well as the optics or the electronics are not modified since the prelaunch determinations. Nevertheless, there is some evidence that the SPOT interferometer filters are affected by outgassing effects during the launch. Tests in vacuum chambers indicated a narrowing of the filters with a shift of the upper side towards the blue of about 10 nm which is more over consistant with the loss of gain observed during the launch. Also, during the lifetime of SPOT, the relationship between the loss of sensitivity and the filter bandwidth may correspond to this effect. On the other hand, the inconsistancy of the NOAA7 calibration between two methods (desert and ocean) having a different spectral sensitivity may indicate a spectral problem with a shift of the central wavelength of -20 nm. The basic idea here is to take advantage of the good spectral definition of AVIRIS to monitor these potential spectral degradations with an experimental opportunity provided by a field campaign held in La Crau (S.E. of France) in June 1991 which associated ground-based measurements and AVIRIS, SPOT2, NOAA-11 overpasses over both the calibration site of La Crau and an agricultural area.

Willart-Soufflet, Veronique↗

NASA NTRS1994

Atomic oxygen fluorescence excitation using a Raman-shifted, tunable ArF-excimer laser

A novel method for exciting the two-photon, 2p3 3p 3P left arrow 2p4 3P atomic oxygen transition is reported. The transition to the upper state is achieved through the combined absorption of photons from the second and third Stokes order pulses of an ArF-excimer laser that is wavelength-shifted by the use of deuterium Raman cell. All three transitions from the ground electronic state of the oxygen atom lie within the tuning range of the Raman-shifted ArF laser. The available pulse energy from this laser configuration is comparable to that of commercially available Nd:YAG-pumped dye laser systems operated at 226 nm.

Fletcher, D. G.↗

NASA NTRS1994

Temperature dependence of Lorentz air-broadening and pressure-shift coefficients of (12)CH4 lines in the 2.3-micron spectral region

High-resolution (0.01/cm) absorption spectra of lean mixtures of CH4 in dry air were recorded with the McMath-Pierce Fourier transform spectrometer (FTS) of the National Solar Observatory on Kitt Peak at various temperatures between 24 and -61 C. The spectra have been analyzed to determine the values at room temperature of pressure-broadened widths and pressure-induced shifts of more than 740 transitions. The temperature dependence of air-broadened widths and pressure-induced shifts was deduced for approx. 370 transitions in the nu(sub 1) + nu(sub 4), nu(sub 3) + nu(sub 4), and nu(sub 2) + nu(sub 3) bands of (12)CH4 located between 4118 and 4615/cm. These results were obtained by analyzing a total of 29 spectra simultaneously using a multi-spectral non-linear least-squares fitting technique. This new technique allowed the determination of correlated spectral line parameters (e.g. intensity and broadening coefficient) better than the procedure of averaging values obtained by fitting the spectra individually. This method also provided a direct determination of the uncertainties in the retrieved parameters due to random errors. For each band analysed in this study the dependence of the various spectral line parameters upon the tetrahedral symmetry species and the rotational quantum numbers of the transitions is also presented.

Devi, V. Malathy↗

NASA NTRS1995

Thermal Line Shift and Broadening of Ho(3+) in Y3AI5O12 and Lu3AIO12

The interaction between the active ion and the host lattice manifests itself in two distinct ways: the static interaction with the crystal field that causes the splitting of the free ion energy levels and the active interaction through the surrounding phonon system that produces temperature dependent characteristics in the optical spectrum of the ion (e.g. line broadening and line shift). The strength of the splitting depends heavily on the electronic configuration of the atom. The model give by McCumber and Sturge describes the thermal effects on line width and position above 77 K with Raman scattering of Debye model phonons. These processes predict a Lorentzian line shape. However, below 77 K the principal contributions are from crystal inhomogeneities that result in a Gaussian line shape. We have investigated the experimental Stark levels as well as the thermal effects on the line width and the position of trivalent holmium ions in both yttrium aluminum garnet, Y3Al5O12 (YAG) and lutetium aluminum garnet, Lu3Al5O12 (LuAG) crystals. We have compared the Stark levels of the (5)I(6) state, and the thermal line shift and broadening of an isolated transition (Z2 to X13) between the (5)I(8) and (5)I(6) stark levels in these crystals. This transition occurs in the near infrared region at approximately 1117 nm.

Snoke, Elizabeth R.↗

NASA NTRS1995

Frequency shifts of high frequency p-modes

Frequency shifts of high frequency p-modes during the solar cycle are calculated for a non-magnetic polytrope convection zone model. An isothermal chromospheric atmosphere threaded by a uniform horizontal magnetic field is correlated to this model. The relevant observations of such frequency changes are discussed. The calculated simultaneous changes in the field strength and chromospheric temperature result in the frequency shifts that are similar to those of the observations.

Jain, Rekha↗

NASA NTRS1995

Acute exposure to 2G phase shifts the rat circadian timing system

The circadian timing system (CTS) provides internal and external temporal coordination of an animal's physiology and behavior. In mammals, the generation and coordination of these circadian rhythms is controlled by a neural pacemaker, the suprachiasmatic nucleus (SCN), located within the hypothalamus. The pacemaker is synchronized to the 24 hour day by time cures (zeitgebers) such as the light/dark cycle. When an animal is exposed to an environment without time cues, the circadian rhythms maintain internal temporal coordination, but exhibit a 'free-running' condition in which the period length is determined by the internal pacemaker. Maintenance of internal and external temporal coordination are critical for normal physiological and psychological function in human and non-human primates. Exposure to altered gravitational environments has been shown to affect the amplitude, mean, and timing of circadian rhythms in species ranging from unicellular organisms to man. However, it has not been determined whether altered gravitational fields have a direct effect on the neural pacemaker, or affect peripheral parameters. In previous studies, the ability of a stimulus to phase shift circadian rhythms was used to determine whether a stimulus has a direct effect on the neural pacemaker. The present experiment was performed in order to determine whether acute exposure to a hyperdynamic field could phase shift circadian rhythms.

Hoban-Higgins, T. M.↗

NASA NTRS1996

Two-Color Laser Speckle Shift Strain Measurement System

A two color laser speckle shift strain measurement system based on the technique of Yamaguchi was designed. The dual wavelength light output from an Argon Ion laser was coupled into two separate single-mode optical fibers (patchcords). The output of the patchcords is incident on the test specimen (here a structural fiber). Strain on the fiber, in one direction, is produced using an Instron 4502. Shifting interference patterns or speckle patterns will be detected at real-time rates using 2 CCD cameras with image processing performed by a hardware correlator. Strain detected in fibers with diameters from 21 microns to 143 microns is expected to be resolved to 15 mu epsilon. This system was designed to be compact and robust and does not require surface preparation of the structural fibers.

Tuma, Margaret L.↗

NASA NTRS1996

Application of Phase Shifted, Laser Feedback Interferometry to Fluid Physics

We have combined the principles of phase-shifting interferometry (PSI) and laser-feedback interferometry (LFI) to produce a new instrument that can measure both optical path length (OPL) changes and discern sample reflectivity variations. In LFI, coherent feedback of the incident light either reflected directly from a surface or reflected after transmission through a region of interest will modulate the output intensity of the laser. LFI can yield a high signal-to-noise ratio even for low reflectivity samples. By combining PSI and LFI, we have produced a robust instrument, based upon a HeNe laser, with high dynamic range that can be used to measure either static (dc) or oscillatory changes along the optical path. As with other forms of interferometry, large changes in OPL require phase unwrapping. Conversely, small phase changes are limited by the fraction of a fringe that can be measured. We introduce the phase shifts with an electro-optic modulator (EOM) and use either the Carre or Hariharan algorithms to determine the phase and visibility. We have determined the accuracy and precision of our technique by measuring both the bending of a cantilevered piezoelectric bimorph and linear ramps to the EOM. Using PSI, sub-nanometer displacements can be measured. We have combined our interferometer with a commercial microscope and scanning piezoelectric stage and have measured the variation in OPL and visibility for drops of PDMS (silicone oil) on coated single crystal silicon. Our measurement of the static contact angle agrees with the value of 68 deg stated in the literature.

Ovryn, Ben↗

NASA NTRS1990

A Shifted Block Lanczos Algorithm 1: The Block Recurrence

In this paper we describe a block Lanczos algorithm that is used as the key building block of a software package for the extraction of eigenvalues and eigenvectors of large sparse symmetric generalized eigenproblems. The software package comprises: a version of the block Lanczos algorithm specialized for spectrally transformed eigenproblems; an adaptive strategy for choosing shifts, and efficient codes for factoring large sparse symmetric indefinite matrices. This paper describes the algorithmic details of our block Lanczos recurrence. This uses a novel combination of block generalizations of several features that have only been investigated independently in the past. In particular new forms of partial reorthogonalization, selective reorthogonalization and local reorthogonalization are used, as is a new algorithm for obtaining the M-orthogonal factorization of a matrix. The heuristic shifting strategy, the integration with sparse linear equation solvers and numerical experience with the code are described in a companion paper.

Grimes, Roger G.↗

NASA NTRS1995

Collisional Shift and Broadening of Iodine Spectral Lines in Air Near 543 nm

The collisional processes that influence the absorption of monochromatic light by iodine in air have been investigated. Measurements were made in both a static cell and an underexpanded jet flow over the range of properties encountered in typical compressible-flow aerodynamic applications. Experimentally measured values of the collisional shift and broadening coefficients were 0.058 +/- 0.004 and 0.53 +/- 0.010 GHz K(exp 0.7)/torr, respectively. The measured shift value showed reasonable agreement with theoretical calculations based on Lindholm-Foley collisional theory for a simple dispersive potential. The measured collisional broadening showed less favorable agreement with the calculated value.

Fletcher, D. G.↗