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Results for “relative phase angle”

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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Snow and glacier mapping with polarimetric SAR

The objective of this study was to examine the capability of mapping snow and glaciers in alpine regions using synthetic aperture radar (SAR) imagery when topographic information is not available. The topographic effects on the received power for a resolution cell can be explained by the change in illumination area and incidence angle in a slant-rante representation of SAR imagery. The specific polarization signatures and phase difference between HH and VV components are relatively independent of the illuminated are, and the incidence angle has only a small effect on these parameters. They provide a suitable measurement data set for snow and glacier mapping in a high-relief area. The results show that the C-band images of the enhancement factor, the phase difference between HH and VV scattering components, and the normalized cross product of VV scattering elements provide the capability to discriminate among snow with different wetnesses, glaciers, and rocky regions.

Shi, Jiancheng↗
NASA NTRS1988

Fast Synchronization With Burst-Mode Digital Signals

Oscillator quickly synchronized with data clock. Sampling clock synchronized with sinusoid by feedback technique. Signal is measure of phase-error angle theta and generated digitally by technique related to calculation of theta from periodic samples of sinusoid.

Lee, Lin-Nan↗
NASA NTRS1989

Photometric lightcurve observations and reduction techniques

Photoelectric light curves were used to determine the period of rotation, obtain the estimates of shape and pole orientation, and define the phase relation, or brightness as a function of solar phase angle, of asteroids. Methods for taking and reducing observations are described, with particular consideration given to the correction for atmospheric extinction, the use of Fourier analysis in constructing composite light curves, and the analysis of errors. Also discussed are computer programs that solve two principal problems: the determination of the time-variable extinction function for a night and the constuction of composite light curves.

Harris, A. W.↗
NASA NTRS1981

Saturn's rings - Azimuthal variations, phase curves, and radial profiles in four colors

Four-color photographic photometry, at effective wavelengths of 5900, 5350, 4150, and 3560 A, obtained during the 1977, 1978, and 1979 Saturn apparitions, were analyzed to determine the ring brightness as a function of wavelength, solar phase angle, ring particle orbital phase (the azimuthal effect), declination of the earth relative to the ring plane (tilt effect), and radial distance from Saturn. Data were obtained using the International Planetary Patrol network when the ring tilt angle B was approximately 16.5, 11.5, and 6 deg, respectively. From the approximately 40,000 original images, 364 were scanned and digitized, along with corresponding calibration exposures. The smearing correction technique used achieved better signal-to-noise by utilizing such constraints as the known width of Cassini's Division on the major axis. The most important observational results were summarized, and included the following: the azimuthal brightness variations for the brighter portion of ring A increased as the ring tilt decreased from B = 26 deg to less than 16 deg, reaching the order of + or 20% with respect to the ansae; they are not detectable for ring B or the outer portion of ring A.

Thompson, W. T.↗
NASA NTRS1994

Cardiovascular regulation in humans in response to oscillatory lower body negative pressure

The frequency response characteristics of human cardiovascular regulation during hypotensive stress have not been determined. We therefore exposed 10 male volunteers to seven frequencies (0.004-0.1 Hz) of oscillatory lower body negative pressure (OLBNP; 0-50 mmHg). Fourier spectra of arterial pressure (AP), central venous pressure (CVP), stroke volume (SV), cardiac output (CO), heart rate (HR), and total peripheral resistance (TPR) were determined and first harmonic mean, amplitude, and phase angles with respect to OLBNP are presented. AP was relatively well regulated as demonstrated by small oscillations in half amplitude (3.5 mmHg) that were independent of OLBNP frequency and similar to unstressed control spectra. Due to the biomechanics of the system, the magnitudes of oscillations in calf circumference (CC) and CVP decreased with increasing frequency; therefore, we normalized responses by these indexes of the fluid volume shifted. The ratios of oscillations in AP to oscillations in CC increased by an order of magnitude, whereas oscillations in CVP to oscillations in CC and oscillations in AP to oscillations in CVP both tripled between 0.004 and 0.1 Hz. Therefore, even though the amount of fluid shifted by OLBNP decreased with increasing frequency, the magnitude of both CVP and AP oscillations per volume of fluid shifted increased (peaking at 0.08 Hz). The phase relationships between variables, particularly the increasing lags in SV and TPR, but not CVP, indicated that efferent responses with lags of 5-6 s could account for the observed responses. We conclude that, at frequencies below 0.02 Hz, the neural system of humans functioned optimally in regulating AP; OLBNP-induced decreases in SV (by as much as 50%) were counteracted by appropriate oscillations in HR and TPR responses. As OLBNP frequency increased, SV, TPR, and HR oscillations increasingly lagged the input and became less optimally timed for AP regulation.

NASA Discipline Cardiopulmonary↗
NASA NTRS1979

Airborne Electronically Steerable Phased Array (AESPA) program

The basic concept and design of a flatplate-fed transmission array are described and system performance requirements are summarized. Particular emphasis is given to the design of the aperture, the radiating element, the phase shifter, the flatplate feed, and the mechanical support structure. Fabrication and testing techniques are considered. Of the three major parameters of interest in demonstrating the performance capabilities of the transmissive array, beamwidth was shown to be the least sensitive to system amplitude and phase errors. Beam pointing angle was also shown to be relatively insensitive to errors. Close agreement between measured and calculated values was found for array gain. The greatest difference was found for array sidelone level.

Source record↗
NASA NTRS2002

Dynamical Models of the Solar System Formation and Evolution

Mark Lewis has extended his them is work by completing a series of N-body simulations of a narrow ring that: is in the location of Saturn's F-ring and is perturbed by a single satellite comparable to Prometheus, but on a circular orbit. We had previously shown how the satellite perturbations can cause a broadly distributed sparse population of ring particles to become concentrated into narrow rings that can be maintained outside of any resonance location. For low optical depths, the collisions between ring particles are highly localized in the peaks of the satellite wakes. The inelastic collisions therefore occur at a particular orbital phase angle so as to damp the azimuthal component of the relative velocities. Since particle positions are not changed by collisions, the semimajor axes of the particles are shifted toward the actual particle positions where the collisions occur. Thus, negative radial diffusion can occur while conserving orbital angular momentum so long as the forced eccentricity is continually re-excited by the satellite. We speculated that the separation between the final ringlets was largely determined by the magnitude of the forced eccentricities induced by the satellite at closest approach. We carried out a series of simulations with a variety of different satellite masses in order to vary the magnitude of the forced eccentricity. We found that indeed the final spacing of the ringlets does increase with the magnitude of the forced eccentricity (Lewis and Stewart 2002). This occurs because neighboring eccentric ringlets drift out of phase with one another due to Keplerian shear and eventually collide with one another, leading to a smaller number of more widely spaced ringlets, The time scale required to form narrow ringlets in these simulations is much shorter than one would expect from standard theories based upon the orbit-averaged torque produced by multiple passes by the satellite. We find that the initial ringlets form in less than two synodic periods and the final state is typically reached in 10 to 20 synodic periods. These studies move us closer to understanding the significantly more complex system of Saturn's F ring, where the perturbation magnitude varies over short temporal and spatial time scales due to the orbital eccentricities of the perturbing satellite. We are currently extending the simulation to allow for an eccentric orbit of the satellite.

Stewart, Glen R.↗
DOE OSTI2022

Fluid – Fluid Interfacial Area and Its Impact on Relative Permeability - A Pore Network Modeling Study

Abstract Relative permeability (kr) is commonly modeled as an empirical function of phase saturation. Although current empirical models can provide a good match of one or two measured relative permeabilities using saturation alone, they are unable to predict relative permeabilities well when there is hysteresis or when physical properties such as wettability change. Further, current models often result in relative permeability discontinuities that can cause convergence and accuracy problems in simulation. To overcome these problems, recent research has modeled relative permeability as a state function of both saturation (S) and phase connectivity (X). Pore network modeling (PNM) data, however, shows small differences in relative permeability for the same S-X value when approached from a different flow direction. This paper examines the impact of one additional Minkowski parameter (Mecke and Arns, 2005), the fluid-fluid interfacial area, on relative permeability to identify if that satisfactorily explains this discrepancy. We calculate the total fluid-fluid interfacial areas (IA) during two-phase (oil/water) flow in porous media using pore network modeling. The area is calculated from PNM simulations using the areas associated with corners and throats in pore elements of different shapes. The pore network is modeled after a Bentheimer sandstone, using square, triangular, and circular pore shapes. Simulations were conducted for numerous primary drainage and imbibition cycles at a constant contact angle of 0° for the wetting phase. Simultaneous measurements of capillary pressure, relative permeability, saturation, and phase connectivity are made for each displacement. Fluid-fluid interfacial area is calculated from the PNM capillary pressure, the fluid location in the pore elements, and the pore element dimensional data. The results show that differences in the relative permeability at the same (S,X) point is explained well by differences in the fluid-fluid interfacial area (IA). That is, for a larger change in IA at these intersection points, the permeability difference is greater. That difference in relative permeability approaches zero as the difference in IA approaches zero. This confirms that relative permeability can be modeled better as a unique function of S, X, and IA. The results also show that an increase in IA restricts flow decreasing the nonwetting (oil) phase permeability. This decrease is caused by an increase in the throat area fraction compared to the corner area as the total area IA increases. The wetting phase relative permeability, however, shows the inverse trend, in that its relative permeability is greater when IA becomes larger owing to a greater fraction of the total area associated with the corners. The area IA, however, impacts the nonwetting phase relative permeability more than the wetting phase relative permeability. Corner flow improves the wetting phase relative permeability because the wetting phase is continuous there. Finally, a sensitivity analysis shows that relative permeability a is more sensitive to change in S than they are for IA for the case studied implying that if only two parameters are used to model relative permeability it is better to choose S and X.

Engineering↗
NASA NTRS1988

Fluctuations and massive separation in three-dimensional shock-wave/boundary-layer interactions

Shock-wave unsteadiness was observed in rapidly compressed supersonic turbulent boundary layer flows with significant separation. A Mach 2.85 shock-wave/turbulent boundary layer flow was set up over a series of cylinder-flare bodies in the High Reynolds Number Channel 1. The transition from fully attached to fully separated flow was studied using axisymmetric flares with increasing compression angles. In the second phase, the 30 deg flare was inclined relative to the cylinder axis, so that the effect on a separated flow of increasing 3 dimensionality could be observed. Two 3-D separated cases are examined. A simple conditional sampling technique is applied to the data to group them according to an associated shock position. Mean velocities and turbulent kinetic energies, computed from the conditionally samples data, are compared to those from the unsorted data and to computed values. Three basic questions were addressed: can conditional sampling be used to provide snapshots of the flow; are averaged turbulence quantities dominated by the bimodal nature of the interaction; and is the shock unsteadiness really important to computational accuracy.

Kussoy, M. I.↗
NASA NTRS1988

Table mountain observatory support to other programs

The Table Mountain Observatory (TMO) facilities include well equipped 24 inch and 16 inch telescopes with a 40 inch telescope (owned by Pomona College) due for completion during FY 89. This proposal is to provide operational support (equipment maintenance, setup, and observing assistnce) at TMO to other programs. The program currently most heavily supported by this grant is the asteroid photometry program directed by A. W. Harris. During 1987, about 20 asteroids were observed, including a near-earth asteroid, 1951 Midas. The photometric observations are used to derive rotation periods, estimate shapes and pole orientations, and to define the phase relations of asteroids. The E class asteroid 64 Angelina was observed, and showed the same opposition spike observed of 44 Jysa, last year. Comet observations are made with the narrow band camera system of David Rees, University College London. Observational support and training was provided to students and faculty from Claremont Colleges for variable star observing programs. Researchers propose to continue the asteroid program, with emphasis on measuring phase relations of low and high albedo asteroids at very low phase angles, and supporting collaborative studies of asteroid shapes.

Harris, Alan W.↗
NASA NTRS1988

Fluctuations and massive separation in three-dimensional shock-wave/boundary-layer interactions

Shock-wave unsteadiness was observed in rapidly compressed supersonic turbulent boundary layer flows with significant separation. A Mach 2.85 shock-wave/turbulent boundary layer flow was set up over a series of cylinder-flare bodies in the High Reynolds Number Channel 1. The transition from fully attached to fully separated flow was studied using axisymmetric flares with increasing compression angles. In the second phase, the 30-deg flare was inclined relative to the cylinder axis, so that the effect on a separated flow of increasing three-dimensionality could be observed. Two 3-D separated cases are examined. A simple conditional sampling technique is applied to the data to group them according to an associated shock position. Mean velocities and turbulent kinetic energies, computed from the conditionally sampled data, are compared to those from the unsorted data and to computed values. Three basic questions were addressed: can conditional sampling be used to provide snapshots of the flow; are averaged turbulence quantities dominated by the bimodal nature of the interaction; and is the shock unsteadiness really important to computational accuracy.

Kussoy, M. I.↗
NASA NTRS1999

IMF Length Scales and Predictability: The Two Length Scale Medium

We present preliminary results from a systematic study using simultaneous data from three spacecraft, Wind, IMP 8 (Interplanetary Monitoring Platform) and Geotail to examine interplanetary length scales and their implications on predictability for magnetic field parcels in the typical solar wind. Time periods were selected when the plane formed by the three spacecraft included the GSE (Ground Support Equipment) x-direction so that if the parcel fronts were strictly planar, the two adjacent spacecraft pairs would determine the same phase front angles. After correcting for the motion of the Earth relative to the interplanetary medium and deviations in the solar wind flow from radial, we used differences in the measured front angle between the two spacecraft pairs to determine structure radius of curvature. Results indicate that the typical radius of curvature for these IMF parcels is of the order of 100 R (Sub E). This implies that there are two important IMF (Interplanetary Magnetic Field) scale lengths relevant to predictability: (1) the well-established scale length over which correlations observed by two spacecraft decay along a given IMF parcel, of the order of a few tens of Earth radii and (2) the scale length over which two spacecraft are unlikely to even observe the same parcel because of its curvature, of the order of a hundred Earth radii.

Collier, Michael R.↗
DOE OSTI2026

Topological shaping of vortex neutron beams using forked phase gratings

Beams of light or matter that carry well-defined states of orbital angular momentum (OAM) are promising probes of topological and textured condensed matter systems such as magnetic skyrmions. Using spin-echo small-angle neutron scattering, a phase-sensitive technique that allows for a relatively low intensity beam, we demonstrate the production of vortex neutron beams from forked phase gratings of various topological charges. This type of interferometric verification of OAM we present here could be further extended to other platforms using probes that are similarly limited by the coherence and strength of the currently available sources.

Cold atoms & matter waves↗
NASA NTRS1987

Titania's opposition effect - Analysis of Voyager observations

Voyager 2 obtained images of Titania over phase angles ranging from 0.8 to 150 deg and at sufficient resolution to investigate the photometric behavior of different surface units. The large, relatively narrow opposition surge detected from earth was confirmed and can be successfully modeled with Hapke's (1986) photometric theory. Opposition effects do not vary greatly between bright areas (craters and ejecta) and dark areas, but the brightness of the brighter areas decreases more slowly with increasing phase angle than that of the dark areas. Thus the fresher craters and their ejecta become less prominent in relation to the background as opposition is approached. This effect is best explained by a modest difference in single-scattering albedo.

Thomas, P. C.↗
NASA NTRS2010

Phase-Array Approach to Optical Whispering Gallery Modulators

This technology leverages the well-defined orbital number of a whispering gallery modulator (WGM) to expand the range of applications for such resonators. This property rigidly connects the phase variation of the field in this mode with the azimuthal angle between the coupling locations. A WGM with orbital momentum L has exactly L instant nodes around the circumference of the WGM resonator supporting such a mode. Therefore, in two locations separated by the arc alpha, the phase difference of such a field will be equal to phi= alpha L. Coupling the field out of such locations, and into a balanced interferometer, once can observe a complete constructive or distractive interference (or have any situation in between) depending on the angle alpha. Similarly, a mode L + delta L will pick up the phase phi + alpha delta L. In all applications of a WGM resonator as a modulator, the orbital numbers for the carrier and sidebands are different, and their differences delta L are known (usually, but not necessarily, delta L = 1). Therefore, the choice of the angle alpha, and of the interferometer arms difference, allows one to control the relative phase between different modes and to perform the conversion, separation, and filtering tasks necessary.

Strekalov, Dmitry↗
NASA NTRS2005

The Atmospheres of Saturn and Titan in the Near-Infrared: First Results of Cassini/VIMS

The wide spectral coverage and extensive spatial, temporal, and phase-angle mapping capabilities of the Visual Infrared Mapping Spectrometer (VIMS) onboard the Cassini-Huygens Orbiter are producing fundamental new insights into the nature of the atmospheres of Saturn and Titan. For both bodies, VIMS maps over time and solar phase angles provide information for a multitude of atmospheric constituents and aerosol layers, providing new insights into atmospheric structure and dynamical and chemical processes. For Saturn, salient early results include evidence for phosphine depletion in relatively dark and less cloudy belts at temperate and mid-latitudes compared to the relatively bright and cloudier Equatorial Region, consistent with traditional theories of belts being regions of relative downwelling. Additional Saturn results include (1) the mapping of enhanced trace gas absorptions at the south pole, and (2) the first high phase-angle, high-spatial-resolution imagery of CH4 fluorescence. An additional fundamental new result is the first nighttime near-infrared mapping of Saturn, clearly showing discrete meteorological features relatively deep in the atmosphere beneath the planet's sunlit haze and cloud layers, thus revealing a new dynamical regime at depth where vertical dynamics is relatively more important than zonal dynamics in determining cloud morphology. Zonal wind measurements at deeper levels than previously available are achieved by tracking these features over multiple days, thereby providing measurements of zonal wind shears within Saturn's troposphere when compared to cloudtop movements measured in reflected sunlight. For Titan, initial results include (1) the first detection and mapping of thermal emission spectra of CO, CO2, and CH3D on Titan's nightside limb, (2) the mapping of CH4 fluorescence over the dayside bright limb, extending to approximately 750 km altitude, (3) wind measurements of approximately 0.5 ms(exp -1), favoring prograde, from the movement of a persistent (multiple months) south polar cloud near 88 deg S latitude, and (4) the imaging of two transient mid-southern-latitude cloud features.

Cassini Mission↗
DOE OSTI2021

Data Mining of Polymer Phase Transitions upon Temperature Changes by Small and Wide-Angle X-ray Scattering Combined with Raman Spectroscopy

The complex physical transformations of polymers upon external thermodynamic changes are related to the molecular length of the polymer and its associated multifaceted energetic balance. The understanding of subtle transitions or multistep phase transformation requires real-time phenomenological studies using a multi-technique approach that covers several length-scales and chemical states. A combination of X-ray scattering techniques with Raman spectroscopy and Differential Scanning Calorimetry was conducted to correlate the structural changes from the conformational chain to the polymer crystal and mesoscale organization. Current research applications and the experimental combination of Raman spectroscopy with simultaneous SAXS/WAXS measurements coupled to a DSC is discussed. In particular, we show that in order to obtain the maximum benefit from simultaneously obtained high-quality data sets from different techniques, one should look beyond traditional analysis techniques and instead apply multivariate analysis. Data mining strategies can be applied to develop methods to control polymer processing in an industrial context. Crystallization studies of a PVDF blend with a fluoroelastomer, known to feature complex phase transitions, were used to validate the combined approach and further analyzed by MVA.

36 MATERIALS SCIENCE↗