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At least 883 records · Page 49

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NASA NTRS2001

Extending unbiased stereology of brain ultrastructure to three-dimensional volumes

OBJECTIVE: Analysis of brain ultrastructure is needed to reveal how neurons communicate with one another via synapses and how disease processes alter this communication. In the past, such analyses have usually been based on single or paired sections obtained by electron microscopy. Reconstruction from multiple serial sections provides a much needed, richer representation of the three-dimensional organization of the brain. This paper introduces a new reconstruction system and new methods for analyzing in three dimensions the location and ultrastructure of neuronal components, such as synapses, which are distributed non-randomly throughout the brain. DESIGN AND MEASUREMENTS: Volumes are reconstructed by defining transformations that align the entire area of adjacent sections. Whole-field alignment requires rotation, translation, skew, scaling, and second-order nonlinear deformations. Such transformations are implemented by a linear combination of bivariate polynomials. Computer software for generating transformations based on user input is described. Stereological techniques for assessing structural distributions in reconstructed volumes are the unbiased bricking, disector, unbiased ratio, and per-length counting techniques. A new general method, the fractional counter, is also described. This unbiased technique relies on the counting of fractions of objects contained in a test volume. A volume of brain tissue from stratum radiatum of hippocampal area CA1 is reconstructed and analyzed for synaptic density to demonstrate and compare the techniques. RESULTS AND CONCLUSIONS: Reconstruction makes practicable volume-oriented analysis of ultrastructure using such techniques as the unbiased bricking and fractional counter methods. These analysis methods are less sensitive to the section-to-section variations in counts and section thickness, factors that contribute to the inaccuracy of other stereological methods. In addition, volume reconstruction facilitates visualization and modeling of structures and analysis of three-dimensional relationships such as synaptic connectivity.

NASA Discipline Neuroscience↗

NASA NTRS1972

Monte Carlo investigation of transient acoustic fields in partially or completely bounded medium

A simple repetitive calculation was used to investigate what happens to the field in terms of the signal paths of disturbances originating from the energy source. The computation allowed the field to be reconstructed as a function of space and time on a statistical basis. The suggested Monte Carlo method is in response to the need for a numerical method to supplement analytical methods of solution which are only valid when the boundaries have simple shapes, rather than for a medium that is bounded. For the analysis, a suitable model was created from which was developed an algorithm for the estimation of acoustic pressure variations in the region under investigation. The validity of the technique was demonstrated by analysis of simple physical models with the aid of a digital computer. The Monte Carlo method is applicable to a medium which is homogeneous and is enclosed by either rectangular or curved boundaries.

Thanedar, B. D.↗

NASA NTRS2018

Reliability of the Danish Aerospace Corporation Portable Pulmonary Function System

Metabolic gas analysis is a critical component of investigations that measure cardio-pulmonary exercise responses during and after long-duration spaceflight. The primary purpose of the current study was to determine the reliability and intra-subject repeatability of a metabolic gas analysis device, the Portable Pulmonary Function System (PPFS), designed for use on the International Space Station (ISS). The second objective of this study was to directly compare PPFS measurements of expired oxygen and carbon dioxide (FEO2 and FECO2) to values obtained from a well-validated clinical metabolic gas analysis system (ParvoMedics TrueOne (c) [PM]). Eight subjects performed four peak cycle tests to maximal exertion. The first test was used to prescribe work rates for the subsequent test sessions. Metabolic gas analysis for this test was performed by the PM, but samples of FEO2 and FECO2 also were simultaneously collected for analysis by the PPFS. Subjects then performed three additional peak cycle tests, consisting of three 5-min stages designed to elicit 25%, 50%, and 75% maximal oxygen consumption (VO2max) followed by stepwise increases of 25 W/min until subjects reached volitional exhaustion. Metabolic gas analysis was performed using the PPFS for these tests. Intraclass correlation coefficients (ICC), within-subject standard deviations (WS SD), and coefficients of variation (CV%) were calculated for the repeated exercise tests. Mixed model regression analysis was used to compare paired FEO2 and FECO2 values obtained from the PPFS and the PM during the initial test. The ICC values for oxygen consumption (VO2), carbon dioxide production (VCO2), and ventilation (VE) indicate that the PPFS is highly reliable (0.79 to 0.99) for all exercise levels tested; however, ICCs for respiratory exchange ratio (RER) were low ( 0.11 - 0.51), indicating poor agreement between trials during submaximal and maximal exercise. Overall, CVs ranged from 1.6% to 6.7% for all measurements, a finding consistent with reported values that were obtained using other metabolic gas analysis techniques. The PPFS and PM produced comparable FEO2 data; however, there was less agreement between measures of FECO2 obtained from the two devices, particularly at lower CO2 concentrations. The PPFS appears, in practically all respects, to yield highly reliable metabolic gas analysis data. Lower reliability of RER measurements reported in the literature and likely is not a function of the PPFS device. Further examination of PPFS CO2 data is warranted to better understand the limitations of these PPFS measurements. Overall, the PPFS when used for repeated measures of cardio-pulmonary exercise should provide accurate and reliable data for studies of human adaptation to spaceflight.

Portable Pulmonary Function System (PPFS)↗

NASA NTRSDate not supplied

TPSAS-NF1676L-17943-DND

SAGE II used the solar occultation technique to measure atmospheric ozone for 21 years between 1984 and 2005 and has continued to play a key role in numerous international assessments. Traditionally, the determination of trends in ozone using SAGE II data has been done via time series analysis of monthly mean data within specific latitude bands. However, given the sparse sampling of SAGE II data, this will introduce temporal and/or spatial biases, particularly in the period after late 2000 when the instrument operated at half-duty cycle. Herein we present a new method for performing time series analysis of unevenly sampled data (in particular SAGE II); namely, we utilize the daily mean data and perform a simultaneous temporal and spatial analysis, making use of a Fourier series to constrain latitudinal variation. This methodology is applied to both the previous (v6.2) and current (v7.0) versions of the SAGE II data. Results are discussed that show the improvements to the data between versions 6.2 and 7.0 that make time series analysis produce reduced residuals as well as the preliminary results of the time series itself, which reveal some of the limitations in currently used proxies for the regression.

Robert P Damadeo↗

NASA NTRSDate not supplied

Solar Migrating Diurnal Tide in the Upper Mesosphere and Lower Thermosphere from SD-WACCM-X, Aura/MLS, and TIMED/SABER

Solar heating on the rotating Earth is a fundamental forcing of atmospheric tidal waves. The migrating diurnal tide, propagating from the troposphere to the upper mesosphere and lower thermosphere, is a large global disturbance that drives most of the daily variations in dynamics, thermal structures, chemistry, as well as atmospheric compositions. In this study, we present a comprehensive analysis of the (1,1) propagating diurnal tides derived from multi-year MLS and SABER observations, to characterize and better understand interannual and long-term tidal variability in the upper atmosphere. Although the (1,1) tide is driven by the solar heating, its interannual variations are largely determined by the internal variability of Earth’s climate system. The tidal amplitudes derived from MLS and SABER data agree well with each other in terms of monthly climatology and interannual variations, showing a consistent seasonal cycle and modulations from the Quasi Biennial Oscillation (QBO). The Ensemble Empirical Mode Decomposition (EEMD) analysis, employed to extract the low frequency variations, also reveals an ENSO-like (42 months) influence on tidal amplitudes in the upper mesosphere. While their (1,1) tidal amplitudes are less affected by the solar cycle, the mean mixing ratio of carbon monoxide (CO) and ozone (O3) is significantly modulated by the 11-year solar cycle due to their UV-dependent photochemistry.

mesosphere↗

NASA NTRS1988

An analysis for high speed propeller-nacelle aerodynamic performance prediction. Volume 1: Theory and application

A computer program, the Propeller Nacelle Aerodynamic Performance Prediction Analysis (PANPER), was developed for the prediction and analysis of the performance and airflow of propeller-nacelle configurations operating over a forward speed range inclusive of high speed flight typical of recent propfan designs. A propeller lifting line, wake program was combined with a compressible, viscous center body interaction program, originally developed for diffusers, to compute the propeller-nacelle flow field, blade loading distribution, propeller performance, and the nacelle forebody pressure and viscous drag distributions. The computer analysis is applicable to single and coaxial counterrotating propellers. The blade geometries can include spanwise variations in sweep, droop, taper, thickness, and airfoil section type. In the coaxial mode of operation the analysis can treat both equal and unequal blade number and rotational speeds on the propeller disks. The nacelle portion of the analysis can treat both free air and tunnel wall configurations including wall bleed. The analysis was applied to many different sets of flight conditions using selected aerodynamic modeling options. The influence of different propeller nacelle-tunnel wall configurations was studied. Comparisons with available test data for both single and coaxial propeller configurations are presented along with a discussion of the results.

Egolf, T. Alan↗

NASA NTRS2009

Stability and Control Analysis of the F-15B Quiet SpikeTM Aircraft

The primary purpose of the Quiet Spike(TradeMark) flight research program was to analyze the aerodynamic, structural, and mechanical proof-of-concept of a large multi-stage telescoping nose spike installed on the National Aeronautics and Space Administration Dryden Flight Research Center (Edwards, California) F-15B airplane. This report describes the preflight stability and control analysis performed to assess the effect of the spike on the stability, controllability, and handling qualities of the airplane; and to develop an envelope expansion approach to maintain safety of flight. The overall flight test objective was to collect flight data to validate the spike structural dynamics and loads model up to Mach 1.8. Other objectives included validating the mechanical feasibility of a morphing fuselage at operational conditions and determining the near-field shock wave characterization. The two main issues relevant to the stability and control objectives were the effects of the spike-influenced aerodynamics on the F-15B airplane flight dynamics, and the air data and angle-of-attack sensors. The analysis covered the sensitivity of the stability margins, and the handling qualities due to aerodynamic variation and the maneuvering limitations of the F-15B Quiet Spike configuration. The results of the analysis and the implications for the flight test program are also presented.

McWherter, Shaun C.↗

NASA NTRS1990

Prediction of the noise from a propeller at angle of attack

An analysis is presented to predict the noise of a propeller at angle of attack. The analysis is an extension of that reported by Mani (1990) which predicted the change in noise due to angle of attack due to both unsteady loading and to azimuthal variation of the radiation efficiency of steady noise sources. Mani's analysis, however, was limited to small angles of attack. The analysis reported herein removes this small angle limitation. Results from the analysis are compared with the data of Woodward (1987, 1988), for a single rotation propeller and for a counter rotating propeller. The comparison shows that including the effect of angle of attack on the steady noise sources significantly improves the agreement with data. Including higher order effects of angle of attack, while changing the predicted noise at far forward and aft angles, has little effect near the propeller plane.

Krejsa, Eugene A.↗

NASA NTRS1994

Wavelets, period-doubling, and time-frequency localization with application to organization of convection over the tropical western Pacific

In this paper, preliminary results in using orthogonal and continuous wavelet transform (WT) to identify period doubling and time-frequency localization in both synthetic and real data are presented. First, the Haar WT is applied to synthetic time series derived from a simple nonlinear dynamical system- a first-order quadratic difference equation. Second, the complex Morlet WT is used to study the time-frequency localization of tropical convection based on a high-resolution Japanese Geostationary Meteorological Satellite infrared (IR) radiance dataset. The Haar WT of the synthetic time series indicates the presence and distinct separation of multiple frequencies in a period-doubling sequence. The period-doubling process generates a multiplicity of intermediate frequencies, which are manifested in the nonuniformity in time with respect to the phase of oscillations in the lower frequencies. Wavelet transform also enables the detection of extremely weak signals in high-order subharmonics resulting from the period-doubling bifurcations. These signals are either undetected or considered statistically insignificant by traditional Fourier analysis. The Morlet WT of the IR radiance dataset indicates the presence of multiple timescales, which are localized in both frequency and time. There are two regimes in the variation of IR radiance, corresponding to the wet and dry periods. Multiple timescales, ranging from semidiurnal, diurnal, synoptic, to intraseasonal with embedding structures, are active in the wet regime. In particular, synoptic variability is more prominent during the wet phase of an intensive intraseasonal cycle. These are not only consistent with, but also show more details than, previous findings by using other techniques. The phase-locking relationships among the oscillations with different time-scales suggest that both synoptic and intraseasonal variations may be mixed oscillations due to the interaction of self-excited oscillations in the tropical atmosphere and external forcings such as annual and diurnal solar radiation variations. Both examples show that WT is a powerful tool for analysis of phenomena involving multiscale interactions that exhibit localization in both frequency and time. A discussion on the caveats in the use of WT in geophysical data analysis is also presented.

Weng, Hengyi↗

NASA NTRS1964

Dynamocardiography

Analysis of cardiac activity by center of gravity variations in human thorax - dynamocardiograph

CARDIOGRAPHY↗

NASA NTRS1974

Determination of the radial gradient in the region 0.81-1.0 AU using both high- and low-energy /more than 10-GeV and more than 52-MeV/ detectors for the 1-AU monitor

A determination of the radial gradient for alpha particles (31-46 MeV/nuc) and protons with energies above 7.5 MeV and 44-77 MeV in the region 1.0-0.81 AU is presented for the solar-quiet year 1966. The determinations are based on data from the Pioneer 6 space probe. Two different detectors are used: the Deep River neutron monitor and measurements of low energy protons made on the IMP-C satellite. The average energy response of the Deep River monitor is 16 GeV, whereas the IMP-C data is for protons with energies above 50 MeV. The resulting radial gradient is found to be nearly zero for the alpha particles and slightly negative for the protons. The same qualitative results were found using the IMP-C data and the Deep River neutron monitor to measure the temporal variation in the cosmic ray intensity. The present analysis indicates that detectors over a wide range of energies are suitable for measuring the radial gradient, providing sufficient statistical precision is obtained to evaluate short-term modulation and the azimuthal separation of the detectors is not great.

Sheldon, W. R.↗

NASA NTRS1976

Discovery of intense X-ray bursts from the globular cluster NGC 6624

A new type of time variation of cosmic X-ray sources has been found from the Astronomical Netherlands Satellite (ANS) observations of the source 3U 1820-30, associated with the globular cluster NGC 6624. Two bursts in the 1-30 keV X-ray intensity of this source are reported. Each displayed a rapid rise in flux (no more than 1 s) by a factor of 20-30 followed by an approximately 8-s exponential decay. These bursts appear to be qualitatively different from short time variations previously reported for X-ray sources. Analysis for further source variability, energy spectra, and position is presented. The characteristics of these events may imply the existence of a collapsed core in the globular cluster.

Grindlay, J.↗

NASA NTRS1977

Design of rotors for improved structural life

Major rotor design criteria are discussed with particular emphasis on those aspects of rotor design that ensure long life component integrity. Dynamic considerations, that necessitate tuning of bladed disk and seal assemblies to avoid excessive vibratory stress at both design and off-design conditions are reviewed as well as low cycle fatigue considerations, which have resulted in detailed analysis procedures to establish part temperature and stress variation throughout an operating cycle and extensive specimen and component fatigue testing to establish safe cyclic operating limits. The frequency, size, and behavior of intrinsic material defects were investigated. Manufacturing process improvements, including the application of increasingly sophisticated inspection techniques and quality control procedures are reviewed in light of their impact on component durability.

Hill, J. T.↗

NASA NTRS1978

Frequency selection and calibration of a water vapor radiometer

The calibration coefficients of existing water vapor radiometers are dependent upon meteorology profiles. This is shown to be due mainly to incorrect frequency pairs. By properly selecting an optimum frequency pair, the dependency can be reduced to a relatively small amount which can be handily adjusted by surface measurement alone. Hence, a universal calibration equation is applicable to all environmental conditions - site, seasonal and diurnal variations. Optimum frequency pairs are systematically searched. Error analysis indicates that calibration for the water vapor phase delay accurate to less than 2 cm is possible at all elevation angles greater than 15 degrees.

Wu, S. C.↗

NASA NTRS1978

An improved analytical model of the separation region on boattail nozzles at subsonic speeds

A practical engineering calculation was developed to model the viscous effects of a separated, reverse flow region on afterbody pressures and drag. This viscous calculation was iteratively coupled with an inviscid flow calculation by means of an aerodynamic interface. A standard boundary layer displacement thickness was used to modify the afterbody shape where the flow was attached. A discriminating streamline calculation was developed to account for displacement effects of the reverse flow in separated regions with and without a flowing jet. The viscous flow calculation was coupled with a potential flow calculation. The analysis accurately predicted afterbody pressures and drag with variations in Reynolds number, Mach number, and afterbody shape.

Presz, W. M., Jr.↗

NASA NTRS1978

Investigations of simulated aircraft flight through thunderstorm outflows

The effects of wind shear on aircraft flying through thunderstorm gust fronts were investigated. A computer program was developed to solve the two dimensional, nonlinear equations of aircraft motion, including wind shear. The procedure described and documented accounts for spatial and temporal variations of the aircraft within the flow regime. Analysis of flight paths and control inputs necessary to maintain specified trajectories for aircraft having characteristics of DC-8, B-747, augmentor wing STOL, and DHC-6 aircraft was recorded. From the analysis an attempt was made to find criteria for reduction of the hazards associated with landing through thunderstorm gust fronts.

Frost, W.↗

NASA NTRS1978

Chemical analysis of positive and negative plates, a survey

Regular arrays of 1 inch discs cut from chemically impregnated positive and negative plates were sent to various contractors and government organizations for chemical analysis in order to determine whether there is consistency in analysis. Techniques used included NASA procedures as specified, variations, wet chemical techniques, and atomic absorption. The weight, thickness of disc, and active material quantity as measured by four respondents are discussed.

Halpert, G.↗

NASA NTRS1981

Effects of temperature fluctuations of IUE data quality

Analysis of IUE calibration lamp images shows that variation in the temperature of the scientific instrument causes shifts in the location of the spectral format with respect to the reseau grid on the detector and in the location of the reseaux themselves. In high dispersion, a camera head amplifier temperature difference of 6C corresponds to a shift of 4 pixels in the spectral format for LWR and 2 pixels for SWP along the dispersion direction. Shifts perpendicular to the disperson (for the same temperature difference) are less than one pixel for both cameras. In low dispersion spectra, the shifts are similar but orthogonal to those described above with the larger motion lying in the direction perpendicular to the dispersion. In both dispersion modes, the observed shifts are apparently independent of wavelength. In high dispersion, the constant pixel shift mimics a constant velocity error.

Thompson, R. W.↗