Showing papers by "Jet Propulsion Laboratory published in 1984"
TL;DR: In this paper, a highly flattened disk has been observed around the fourth-magnitude star Beta Pictoris and it is assumed that the disk is associated with planet formation and that the mass density of the disk falls off with approximately the third power of the radius.
Abstract: A circumstellar disk has been observed optically around the fourth-magnitude star Beta Pictoris. First detected in the infrared by the Infrared Astronomy Satellite last year, the disk is seen to extend to more than 400 astronomical units from the star, or more than twice the distance measured in the infrared by the Infrared Astronomy Satellite. The disk is presented to earth almost edge-on and is composed of solid particles in nearly coplanar orbits. The observed change in surface brightness with distance from the star implies that the mass density of the disk falls off with approximately the third power of the radius. Because the circumstellar material is in the form of a highly flattened disk rather than a spherical shell, it is presumed to be associated with planet formation. It seems likely that the system is relatively young and that planet formation either is occurring now around Beta Pictoris or has recently been completed.
643 citations
TL;DR: It is shown that the broadening in the far-field beam divergence, as well as the broadens of each of the longitudinal modes that were observed in phase-locked arrays, may arise from the excitation of an increasing number of supermodes at increasing pumping levels.
Abstract: The optical characteristics of phase-locked semiconductor laser arrays are formulated in terms of the array supermodes, which are the eigenmodes of the composite-array waveguide, by using coupled-mode theory. These supermodes are employed to calculate the near fields, the far fields, and the difference in the longitudinal-mode oscillation wavelengths of the array. It is shown that the broadening in the far-field beam divergence, as well as the broadening of each of the longitudinal modes that were observed in phase-locked arrays, may arise from the excitation of an increasing number of supermodes at increasing pumping levels.
404 citations
TL;DR: In this paper, the authors display data from the summer of 1981 albacore tuna catch data from concurrent satellite images of sea surface temperature and phytoplankton pigment concentration, from the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) and the Nimbus-7 Coastal Zone Color Scanner (CZCS), respectively.
292 citations
01 Sep 1984
TL;DR: The need for uniform criteria, or guidelines, to be used in all phases of spacecraft design is discussed in this article, and a guide to good design practices for assessing and controlling charging effects is presented.
Abstract: The need for uniform criteria, or guidelines, to be used in all phases of spacecraft design is discussed. Guidelines were developed for the control of absolute and differential charging of spacecraft surfaces by the lower energy space charged particle environment. Interior charging due to higher energy particles is not considered. A guide to good design practices for assessing and controlling charging effects is presented. Uniform design practices for all space vehicles are outlined.
252 citations
TL;DR: Two systolic architectures are developed for performing the product–sum computation AB + C in the finite field GF( 2m) of 2melements, where A, B, and C are arbitrary elements of GF(2m).
Abstract: Two systolic architectures are developed for performing the product–sum computation AB + C in the finite field GF(2m) of 2melements, where A, B, and C are arbitrary elements of GF(2m). The first multiplier is a serial-in, serial-out one-dimensional systolic array, while the second multiplier is a parallel-in, parallel-out two-dimensional systolic array. The first multiplier requires a smaller number of basic cells than the second multiplier. The second multiplier heeds less average time per computation than the first multiplier if a number of computations are performed consecutively. To perform single computations both multipliers require the same computational time. In both cases the architectures are simple and regular and possess the properties of concurrency and modularity. As a consequence they are well suited for use in VLSI systems.
222 citations
TL;DR: A series of automated instruments that use state-of-the-art chemical methods has been developed for high-sensitivity protein sequencing, DNA synthesis and peptide synthesis and their use for the study of a variety of biologically interesting problems.
Abstract: A series of automated instruments that use state-of-the-art chemical methods has been developed for high-sensitivity protein sequencing, DNA synthesis and peptide synthesis. These intruments have been integrated into a centralized microchemical facility in order to promote their use for the study of a variety of biologically interesting problems. This facility has as one of its major functions the development of new chemistries and instrumentation for the structural analysis and synthesis of genes and proteins.
141 citations
TL;DR: In this article, numerical models of subducting slabs were used to explain the global variation of Benioff zone seismicity with depth and the orientation of stress axes of deep and intermediate earthquakes.
96 citations
TL;DR: The development of electrically self calibrated cavity pyrheliometric instrumentation that occurred in the early 20th century provided the technological base for experiments to detect variability of the solar total irradiance as discussed by the authors.
Abstract: The development of electrically self calibrated cavity pyrheliometric instrumentation that occurred in the early 20th century provided the technological base for experiments to detect variability of the solar total irradiance. Experiments from ground based observatories, aircraft and balloons during the 1st half of the 20th century were unable to achieve sufficient accuracy or long term precision to unambiguously detect irradiance variations of solar origin. Refinements in pyrheliometric technology during the 1960's and 1970's and the accessibility of extended experimental opportunities above the earth's atmosphere in recent years have provided the first direct observations of solar total irradiance variability and provided the cornerstone observations of a long term database on solar irradiance. A program of solar irradiance monitoring has evolved to sustain the database over at least 22 years, corresponding to a single cycle of solar magnetic activity, and the shortest well identified cycle of climate variation. Direct links between total irradiance variations, solar magnetic activity and the solar global '5 min' oscillation phenomena have been derived from recent space flight observations by the SMM/ACRIM I experiment.
92 citations
TL;DR: This paper advocates and summarizes the use of the WBS in software implementation projects, and identifies some of the problems people have had generating software WBSs, and the need for standard checklists of items to be included.
90 citations
TL;DR: The basic idea is the construction of equivalent circular state-diagrams, wherefrom the transform-domain description of the stochastic acquisition process is derived and the method circumvents any complicated time-domain combinatorial arguments.
Abstract: A simple circular state-diagram method has been recently proposed [1], [2] for the modeling, analysis, and optimization of straight serial search code acquisition in spread-spectrum systems. Herein, the approach is generalized to arbitrary serial strategies, such as the Z -search expanding window search, etc., and arbitrary a priori probability distributions for the code phase uncertainty. The basic idea is the construction of equivalent circular state diagrams, wherefrom the transform domain description, i.e., the generating or characteristic function of the stochastic acquisition process is derived. This general method is readily systematized, circumvents the need for complicated time-domain combinatorial arguments, and allows past results [3], [4] to be obtained as particular examples. In principle, the generating function can be used to calculate any moment of the acquisition process; here, however, due to complexity considerations, we restrict our attention to the first moment and its associated performance measure, the mean acquisition time. Based on the derived analytical expressions for the mean acquisition time, an expanding-window single-dwell search strategy has been optimized in terms of the required number of partial windows, parameterized by the prior distribution of the phase uncertainty.
80 citations
TL;DR: In this paper, the rotation period and amplitude of variation of the asteroids 82 Alkmene and 444 Gyptis were determined by using the Lumme and Bowell (1981) theoretical phase function, when only the multiple scattering parameter and zero phase angle are treated as variables.
TL;DR: The present absolute measurements of Titan, Uranus and Neptune geometric albedo spectra in the 3500-10,500 A range have a resolution of about 7 A, together with high SNR, in virtue of the exceptional effeciency of the spectrograph and Reticon detector employed.
TL;DR: Comparison of the times of occurrence of a newly discovered type of disturbance in the interplanetary magnetic field with the passage of the small Venus-crossing asteroid reveals a possible association, but the source of these disturbances appears to be associated with outgassing material in the Oljato orbit some distance behind the asteroid and not with the asteroid itself.
Abstract: Comparison of the times of occurrence of a newly discovered type of disturbance in the interplanetary magnetic field at 0.72 astronomical unit with the passage of the small Venus-crossing asteroid, 2201 Oljato, reveals a possible association, but the source of these disturbances appears to be associated with outgassing material in the Oljato orbit some distance behind the asteroid and not with the asteroid itself. This suggested association can account for one quarter of the total number of events seen in eight Venus years.
TL;DR: The nickel hydroxide electrode has evolved over nearly 100 years from the pocket electrode structure through to the present design of a light weight, porous, plaque structure as discussed by the authors, which provides the essential properties for storing and converting the chemical energy into electrical energy and vice versa.
TL;DR: The outer edges of Saturn's A and B rings, at 2.27 R and 1.95 R, have been examined using data acquired by four Voyager experiments as discussed by the authors, and the shapes and kinematics of these features are influenced by their proximity to strong low-order Lindblad resonances.
TL;DR: Voyager images of Saturn's satellite Iapetus ranging in phase angle from 8 to 90 deg have been used to define the satellite's photometric properties and construct an albedo map of its surface as discussed by the authors.
TL;DR: The Infrared Astronomical Satellite (IRAS) science team has discovered a shell of particulate material around the star Vega, probably a ring of cometary bodies with an estimated minimum mass of 15 earth masses, analogous to one that has been hypothesized for the solar system.
Abstract: The Infrared Astronomical Satellite (IRAS) science team has discovered a shell of particulate material around the star Vega. At the mean distance and temperature of the shell, the expected condensation products from a protostellar nebula would be dominated by frozen volatiles, in particular water ice. It is not possible to discriminate between dirty ice and silicate materials in the Vega shell on the basis of the IRAS data. The Vega shell is probably a ring of cometary bodies with an estimated minimum mass of 15 earth masses, analogous to one that has been hypothesized for the solar system. A possible hot inner shell around Vega may be an asteroid-like belt of material a few astronomical units from the star.
TL;DR: The Infrared Astronomical Satellite (IRAS) as discussed by the authors is the first space telescope to perform observations in the far infrared from orbit, which was launched from Vandenberg Air Force Base on January 25, 1983 into a 900 km orbit.
Abstract: The Infrared Astronomical Satellite (IRAS) is the first space telescope to perform observations in the far infrared from orbit. IRAS was launched from Vandenberg Air Force Base on January 25, 1983 into a 900 km orbit. The satellite is surveying the entire sky in four bands covering the wavelengths from 8 to 120 micrometers. The satellite performance is excellent. With 25% of the data reduced, 262,000 point sources and 80,000 extended sources have been detected.1 IRAS has the first large superfluid helium dewar in space and is expected to last approximately 345 days.
TL;DR: In this article, a simple concise formula is derived for the area of a projection of an ellipsoid, and this expression is used to obtain a general formula for the projected, visible, illuminated area of the triaxial ellipssoid for arbitrary sun-earth-asteroid geometry.
Abstract: The determination of the light curve (LC) of a geometrically scattering ellipsoid is considered in relation to the problem of investigating the physical properties of asteroids. A simple concise formula is derived for the area of a projection of an ellipsoid, and this expression is used to obtain a general formula for the projected, visible, illuminated area of a triaxial ellipsoid for arbitrary sun-earth-asteroid geometry. It is found that the LC of an ellipsoid has special properties that can be exploited to test the hypothesis that a given optical or radar LC could be due to a geometrically scattering ellipsoid.
TL;DR: In this article, 11 analyzed lava samples from Ponape island are alkali olivine basalt, basanite and basanitoid, and most of them are aphyric or sparsely phyric (< 10% phenocrysts).
TL;DR: In this article, the velocity field in the neighborhood of the high-speed jet located at approximately 24 deg N latitude in the Jovian atmosphere was measured and the maximum zonal velocity was found to be 182 + or 10 m/s, located at 23.7 + or 0.2 deg N and representing the largest velocity measured on the planet.
TL;DR: In this article, the effects of the secondary noise source of phase scintillations caused by interstellar electron density fluctuations are calculated, and the prospects for improved ultralow frequency (ULF) gravitational wave measurements using pulsar timing are discussed.
Abstract: High precision pulsar timing measurements have been used to set upper limits on the flux of ultralong period (T greater than 3 years) stochastic gravitational waves. The data used to produce the current limits appear to be limited by timing noise that is intrinsic to the pulsars. Recently, however, there have been very low noise timing observations of the 1.5-millisecond pulsar. This suggests that significant sensitivity improvements in searches for ultralow frequency (ULF) gravitational waves may be possible. Here, the effects of the heretofore secondary noise source of phase scintillations caused by interstellar electron density fluctuations are calculated, and the prospects for improved ULF gravitational wave measurements using pulsar timing are discussed.
TL;DR: In this article, the first measurement of single event upset (SEU) for complementary GaAs static RAMs caused by heavy ions is reported, and the circuit cross-sections of the circuits for 28 MeV oxygen ions are reported as well as the linear energy transfer (LET) threshold established by using 170 MEV oxygen ion at various angles of beam incidence.
Abstract: The first measurement of single event upset (SEU) for complementary GaAs static RAMs caused by heavy ions is reported. Upset cross-sections of the circuits for 28 MeV oxygen ions are reported as well as the linear energy transfer (LET) threshold established by using 170 MeV oxygen ions at various angles of beam incidence.
01 Jan 1984
TL;DR: In this article, the authors used the twice-daily humidity soundings from radiosonde reports in 1978 at Barbados, Puerto Rico, Bermuda and Ocean Weather Station P to examine the water vapor distribution in the atmosphere.
Abstract: The twice-daily humidity soundings from radiosonde reports in 1978 at Barbados, Puerto Rico, Bermuda and Ocean Weather Station P are used to examine the water vapor distribution in the atmosphere. The specific humidity at the lowest sounding level is found to correlate very well with the integrated water vapor in the atmospheric column at monthly time scale. An empirical relation between these two quantities is determined.
01 Jan 1984
Abstract: The effect of climate warming on the size of ice sheet margins in polar regions is considered Particular attention is given to the possibility of a rapid response to warming on the order of tens to hundreds of years It is found that the early response of the polar regions to climate warming would be an increase in the area of summer melt on the ice sheets and ice shelves For sufficiently large warming (5-10C) the delayed effects would include the breakup of the ice shelves by an increase in ice drainage rates, particularly from the ice sheets On the basis of published data for periodic changes in the thickness and melting rates of the marine ice sheets and fjord glaciers in Greenland and Antarctica, it is shown that the rate of retreat (or advance) of an ice sheet is primarily determined by: bedrock topography; the basal conditions of the grounded ice sheet; and the ice shelf condition downstream of the grounding line A program of satellite and ground measurements to monitor the state of ice sheet equilibrium is recommended
TL;DR: A new digital processing algorithm is developed for producing images from SEASAT synthetic aperture radar (SAR) data that applies the fast polynomial transform for computing the two-dimensional cyclic correlation of the raw echo data with the impulse response of a point target.
Abstract: In this paper, a new digital processing algorithm is developed for producing images from SEASAT synthetic aperture radar (SAR) data. For reasons of ecomony, SEASAT presently operates in the stripmapping mode rather than the potentially higher resolution spotlight mode [1]. This algorithm applies the fast polynomial transform (FPT) for computing the two-dimensional cyclic correlation of the raw echo data with the impulse response of a point target. This two-dimensional correlation algorithm solves the range migration problem. It is demonstrated that this SAR processing technique is readily implemented on a general purpose computer. Actual results of SEASAT SAR imagery are given in this paper.
21 May 1984
TL;DR: It is shown that a low power pilot tone can be used to continuously calibrate a mobile link against time varying impairments and coherent demodulation of data is possible by means of the pilot tone without using a conventional tracking loop.
Abstract: Random amplitude and phase modulations experienced in mobile channels result in a number of system limitations and link impairments. In this paper, a novel approach named "tone calibrated technique" which mitigates multipath fading induced distortions in a digital link is presented. It is shown that a low power pilot tone can be used to continuously calibrate a mobile link against time varying impairments. Coherent demodulation of data is possible by means of the pilot tone without using a conventional tracking loop. Since very little power is consumed by the pilot tone, the performance of the tone calibrated technique is only marginally below BPSK in an unfaded environment.
TL;DR: Radiation-mediated grafting of polyacrolein onto poly(methyl methacrylate) microspheres has been shown to activate the particles for chymotrypsin (EC 3.4.21) immobilization.
TL;DR: In this article, a physically reasonable mean flow was found which leads to theoretically predicted tides that are in excellent agreement with those observed, with a maximum velocity of about 130 m/sec at 70 km altitude, decreasing to about zero at 88 km, together with a jet-like meridional structure.
Abstract: The 1978 Pioneer Venus mission, in addition to producing strong IR radiometer experiment evidence for the existence of a semidiurnal solar tide in the Venus mesosphere, has yielded radiative flux and cloud particle distribution data about the structure of solar heating and IR cooling which facilitate calculations of tidal forcing functions and estimates of radiative dissipation rates. It is presently shown that a physically reasonable mean flow can be found which leads to theoretically predicted tides that are in excellent agreement with those observed. The zonal mean flow obtained exhibits a maximum velocity of about 130 m/sec at 70 km altitude, decreasing to about zero at 88 km, together with a jet-like meridional structure that strongly deviates from solid body rotation.