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Feedback circuit controls fluctuations in speed of synchronous ac motor. Voltage proportional to phase angle is developed by phase detector, rectified, amplified, compared to threshold, and reapplied positively or negatively to motor excitation circuit. Speed control reduces wow and flutter of audio turntables and tape recorders, and enhances hunting in gyroscope motors.
Observations of Titan's whole-disk polarization at 2460 and 7500 A are presented and analyzed in terms of model scattering atmospheres. If the Titan aerosols are spherical or nearly spherical, no single combination of refractive index and size distribution is able to fit data at both wavelengths. However, a vertically inhomogeneous distribution suggested by Tomasko and Smith (1980), characterized by a size gradient with altitude, fits the data at 2640 A moderately well but must be modified at intermediate and large optical depths to fit the 7500-A data. Results for synthetic phase functions indicate that the single-scattering polarization must be 70 percent or larger in the UV and 78 percent or larger in the near-IR at 90-deg phase angle, depending on the phase function. If the correct phase function is similar to that for 0.5-micron-radius spheres, the UV single-scattered polarization must be 84 percent and the near-IR single-scattered polarization must be over 90 percent. Such large polarizations are impossible for 0.5-micron-radius spheres but may be possible for nonspherical particles with effective radii near 0.5 micron, although the existence of nonspherical particles with the scattering properties required by these and other observations has not been demonstrated.
Voyager images of Amalthea are presented, which reveal an irregular satellite in synchronous rotation relative to Jupiter with dimensions of 270 x 165 x 150 km. The surface appears scarred by large craters and sharp ridges to indicate a history of cosmic battering. Amalthea'a normal surface reflectance is 5-6% with a very red color and a mean opposition angle magnitude of +14. The phase coefficient between phase angles of 0.8 and 42 deg of 0.042 + or - 0.004 mag/deg indicates that the phase integral does not exceed 0.3 and the Bond Albedo is less than 0.02. Several prominent bright spots of 10-50 km across occur on local slopes and ridges, have albedos several times higher than the background, and have a greenish color where the spectrum bends down beyond 0.56 microns.
A hybrid inverter-based resource (IBR) power plant consists of grid-following (GFL) and grid-forming inverter-based resources (GFM-IBR) connected in parallel. Here, this research focuses on how to design and tune GFM's control parameters to ensure stable operation of the hybrid power plant for weak and strong grid conditions. We consider two design cases: one where the GFL-IBR does not provide frequency support, and one where it does. It is found that the GFM's power-frequency synchronizing system can lose stability when the power-frequency droop constant is large and/or the grid is strong. Additionally, if the GFL has its frequency support enabled, oscillation stability worsens. To explain the mechanism of the interactions, we construct a feedback system for the synchronizing loop, which consists of the GFM's power-frequency droop control that generates the GFM's synchronizing angle, the GFL's phase-locked loop that measures the voltage phase angle, the GFL's frequency-power control that generates its power order, and the rest of the system. The feedback system is effective in illustrating the potential stability risks. Successful design ensures that the hybrid power plant can operate smoothly and ride through grid disturbances.
This paper discusses the albedoes and phase angle effects found for 400 members of eight debris swarms using observations obtained in 1990 and 1991 with the NASA Johnson Space Center CCD-equipped portable Schmidt telescope. The mean albedo derived by comparing optical brightnesses with averaged radar cross sections (RCS's) is 10 percent. The standard deviation in log albedo is 0.40 if the RCS's are assumed to contribute equally to the scatter. The RCS's used in this work are the median values obtained by comparing data from 47 separate RCS catalog updates. Forty objects are sufficiently free of tumble or aspect angle effects to yield consistent phase function slopes. These range from specular in nature (zero slope) through Lambertian (moderate slope) to lunar (steep slope) with the mean lying midway between specular and Lambertian.
This paper describes an aeroelastic analysis program for turbomachines. Unsteady Navier-Stokes equations are solved on dynamically deforming, body fitted, grid to obtain the aeroelastic characteristics. Blade structural response is modeled using a modal representation of the blade and the work-per-cycle method is used to evaluate the stability characteristics. Nonzero interblade phase angle is modeled using phase-lagged boundary conditions. Results obtained showed good correlation with existing experimental, analytical, and numerical results. Numerical analysis also showed that given the computational resources available today, engineering solutions with good accuracy are possible using higher fidelity analyses.
This paper describes the calculation of flutter stability characteristics for a transonic forward swept fan configuration using a viscous aeroelastic analysis program. Unsteady Navier-Stokes equations are solved on a dynamically deforming, body fitted, grid to obtain the aeroelastic characteristics using the energy exchange method. The non-zero inter-blade phase angle is modeled using phase-lagged boundary conditions. Results obtained show good correlation with measurements. It is found that the location of shock and variation of shock strength strongly influenced stability. Also, outboard stations primarily contributed to stability characteristics. Results demonstrate that changes in blade shape impact the calculated aerodynamic damping, indicating importance of using accurate blade operating shape under centrifugal and steady aerodynamic loading for flutter prediction. It was found that the calculated aerodynamic damping was relatively insensitive to variation in natural frequency.
We present results from an ongoing program to perform UV measurements (215.0 and 237.0 nm) of the Moon at varying solar phase angles to understand the lunar phase curve at ultraviolet wave- lengths.
We present results from an ongoing program to perform UV measurements of the Moon at varying solar phase angles to understand the lunar phase curve at ultraviolet wavelength.
Theoretical models for lunar brightness at small phase angles and polarization of moonlight
Contrary to published reports, the limb-darkening observed by Mariner 10 is consistent with the sulfuric-acid aerosol scattering that explains the polarization and spectroscopic features of Venus. A combination of both geometric and photometric systematic errors explains the previously reported discrepancy. Although the aerosol model cannot be distinguished from isotropic scattering at the Mariner 10 phase angle, Venera 9 data at larger phases clearly favor the aerosol model. There is no evidence for isotropic scattering in the clouds of Venus.
We studied the phase relationships of the cardiogenic oscillations in the phase III portion of single-breath washouts (SBW) in normal gravity (1 G) and in sustained microgravity (microG). The SBW consisted of a vital capacity inspiration of 5% He-1.25% sulfurhexafluoride-balance O2, preceded at residual volume by a 150-ml Ar bolus. Pairs of gas signals, all of which still showed cardiogenic oscillations, were cross-correlated, and their phase difference was expressed as an angle. Phase relationships between inspired gases (e.g., He) and resident gas (n2) showed no change from 1 G (211 +/- 9 degrees) to microG (163 +/- 7 degrees). Ar bolus and He were unaltered between 1 G (173 +/- 15 degrees) and microG (211 +/- 25 degrees), showing that airway closure in microG remains in regions of high specific ventilation and suggesting that airway closure results from lung regions reaching low regional volume near residual volume. In contrast, CO2 reversed phase with He between 1 G (332 +/- 6 degrees) and microG (263 +/- 27 degrees), strongly suggesting that, in microG, areas of high ventilation are associated with high ventilation-perfusion ratio (VA/Q). This widening of the range of VA/Q in microG may explain previous measurements (G.K. Prisk, A.R. Elliott, H.J.B. Guy, J.M. Kosonen, and J.B. West J. Appl. Physiol. 79: 1290-1298, 1995) of an overall unaltered range of VA/Q in microG, despite more homogeneous distributions of both ventilation and perfusion.
Method of measuring the relative phase angle between two signals of the same frequency with- out the use of modulators or frequency translators
Recent calculations and computer simulations of the right-hand resonant ion beam instability have indicated that gyrophase-bunched ion distributions may be generated as a first step in the disruption of field-aligned beams. Theory predicts a distinct phase angle relationship between the gyrovelocity of the phase-bunched ions and the wave magnetic field. In this paper, observations of such a relationship between gyrophase-bunched ions and MHD-like waves upstream from the earth's bow shock are presented. The observed phases are in accord with the theoretical predictions of the right-hand resonant ion beam instability.
Observations of the September 16, 1984 occultation of SAO 146599 by the C-type asteroid 47 Aglaja from 13 sites in the continental U.S. have yielded a diameter of 136.4 + or - 1.2 km, leading to the calculation of a rotational period of 13.2 + or - 0.01 hr. At the time of the occultation, the zero-phase-angle visual geometric albedo of the asteroid's phase was 0.071 + or - 0.002. It is suggested that a substantial portion of the object's mean brightness variation with ecliptic longitude is ascribable to albedo differences over its surface.
The azimuthal, far field directivity of a scale fan model was measured in high resolution. The model is a 12 inch diameter rotor with 16 blades followed by 40 stator vanes. The tests were conducted at the nominal 100% speed corresponding to a tip speed of 905 ft/sec. Measurement of the radiated sound field, forward of the fan, was made in an anechoic chamber with an inflow control device and a baffle separating the aft and forward radiated interaction noise. The acoustic field was surveyed with a circular hoop array of 16 microphones which was moved to 14 axial stations. At each axial station the hoop was rotated in half-degree increments to take 736 points in the azimuthal angle. In addition to sound pressure level, the phase angle relative to a reference microphone was measured at each point. The sound pressure level is shown to vary in patterns by 10-15 dB especially for the fundamental tone but also for the first and second harmonic. A far field mode detection method has been developed and used with the data which determines the modes generated by the fan and which then interact to form the azimuthal directivity.
Pioneer 11 measurements of Titan's limb darkening and polarization at red and blue wavelengths are refined, and the integrated disk brightness measurements at phase angles from 22 to 96 deg, over which Titan's phase coefficient averages about 0.014 magnitudes/deg in both colors, are reduced. Comparisons of the data with vertically homogeneous multiple scattering models indicate that the single-scattering phase functions of the aerosols in both colors are flat at scattering angles between 80 and 150 deg, with a small peak at larger scattering angles. Although a vertically homogeneous model in which particles are assumed to scatter as spheres cannot simultaneously match the polarization observations of both colors for any refractive index, observed polarizations are most sensitive to the particle properties near optical depth 1/2 in each color. Models based on single scattering by spheres can therefore be successful over a range of refractive indices, if the size of the particles increases with depth and if the cross section of the particles increases sufficiently rapidly with decreasing wavelength.